U.S. patent application number 13/058027 was filed with the patent office on 2011-06-09 for li-containing alpha-sialon-based phosphor, production process thereof, lighting device and image display device.
This patent application is currently assigned to UBE INDUSTRIES, LTD.. Invention is credited to Hiroshi Oda, Takuma Sakai, Shin-ichi Sakata.
Application Number | 20110133629 13/058027 |
Document ID | / |
Family ID | 41669010 |
Filed Date | 2011-06-09 |
United States Patent
Application |
20110133629 |
Kind Code |
A1 |
Sakata; Shin-ichi ; et
al. |
June 9, 2011 |
LI-CONTAINING ALPHA-SIALON-BASED PHOSPHOR, PRODUCTION PROCESS
THEREOF, LIGHTING DEVICE AND IMAGE DISPLAY DEVICE
Abstract
An Li-containing .alpha.-sialon-based phosphor represented by
the formula (1):
Li.sub.xEu.sub.ySi.sub.12-(m+n)Al.sub.(m+n)O.sub.n+.delta.N.sub.16-n-
-.delta. (wherein assuming that average valence of Eu is a,
x+ya+.delta.=m; 0.45.ltoreq.x<1.2, 0.001.ltoreq.y.ltoreq.0.2,
0.9.ltoreq.m.ltoreq.2.5, 0.5.ltoreq.n.ltoreq.2.4, and
.delta.>0).
Inventors: |
Sakata; Shin-ichi;
(Yamaguchi, JP) ; Oda; Hiroshi; (Yamaguchi,
JP) ; Sakai; Takuma; (Yamaguchi, JP) |
Assignee: |
UBE INDUSTRIES, LTD.
Ube-shi, Yamaguchi
JP
|
Family ID: |
41669010 |
Appl. No.: |
13/058027 |
Filed: |
August 11, 2009 |
PCT Filed: |
August 11, 2009 |
PCT NO: |
PCT/JP2009/064373 |
371 Date: |
February 8, 2011 |
Current U.S.
Class: |
313/483 ;
252/301.4F |
Current CPC
Class: |
C09K 11/0883 20130101;
C09K 11/7728 20130101; C09K 11/7734 20130101; Y02B 20/181 20130101;
H01L 33/502 20130101; Y02B 20/00 20130101 |
Class at
Publication: |
313/483 ;
252/301.4F |
International
Class: |
H01J 1/62 20060101
H01J001/62; C09K 11/80 20060101 C09K011/80 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 13, 2008 |
JP |
2008-208569 |
Aug 13, 2008 |
JP |
2008-208570 |
Mar 2, 2009 |
JP |
2009-048453 |
Claims
1. An Li-containing .alpha.-sialon-based phosphor represented by
formula (I):
Li.sub.xEu.sub.ySi.sub.12-(m+n)Al.sub.(m+n)O.sub.n+.delta.N.sub.16--
n-.delta. (1) (wherein assuming that average valence of Eu is a,
x+ya+.delta.=m; 0.45.ltoreq.x<1.2, 0.001.ltoreq.y.ltoreq.0.2,
09.ltoreq.m.ltoreq.2.5, 0.5.ltoreq.n.ltoreq.2.4, and
.delta.>0).
2. The phosphor as claimed in claim 1, wherein said .delta. is from
0.05 to 1.2 and a ratio x/m between x and m is from 0.4 to 0.9.
3. The phosphor as claimed in claim 2, wherein said x is
0.82.ltoreq.x<1.2 and said x/m is from 0.5 to 0.9.
4. The phosphor as claimed in claim 1, wherein fluorescence having
a peak wavelength of 560 to 580 nm is emitted by injecting
excitation light.
5. The phosphor as claimed in claim 1, which is a powder wherein an
average aspect ratio of primary particles as measured by image
analysis of a scanning electron micrograph is 2 or less and average
particle diameter D.sub.particle is from 1 to 3.0 .mu.m.
6. The phosphor as claimed in claim 5, wherein in the particles
measured by the image analysis of the scanning electron micrograph,
a primary particle of 0.8 .mu.m or more is present in an area ratio
of 70% or more.
7. The phosphor as claimed in claim 5, wherein a frequency
distribution curve in a particle size distribution curve measured
by a laser diffraction/scattering particle size distribution
measuring apparatus is a single peak and median diameter is from 4
to 15 .mu.m.
8. The phosphor as claimed in claim 5, wherein the 10% diameter in
the particle size distribution curve is 1.5 .mu.m or more and the
90% diameter is 15 .mu.m or less.
9. The phosphor as claimed in claim 1, which is a powder wherein
aspect ratio of a primary particle as measured by image analysis of
a scanning electron micrograph is 3 or less and length of a short
axis is more than 3 .mu.m.
10. A process for producing the Li-containing .alpha.-sialon-based
phosphor claimed in claim 1, comprising weighing and mixing a
silicon nitride powder and/or a nitrogen-containing silane
compound, an AlN-containing substance working out to an aluminum
source, a nitride, oxynitride or oxide of Li or a precursor
substance capable of becoming an oxide of Li by pyrolysis, and a
nitride, oxynitride or oxide of Eu or a precursor substance capable
of becoming an oxide of Eu by pyrolysis, to give a composition
containing lithium in excess over the composition of the
Li-containing .alpha.-sialon-based phosphor represented by formula
(I), and firing the mixture at 1,400 to 1,800.degree. C. in a
nitrogen-containing inert gas atmosphere under atmospheric
pressure.
11. The process of claim 10, wherein the Li-containing
.alpha.-sialon-based phosphor after firing is subjected to acid
washing.
12. A process for producing the phosphor of claim 5, comprising
weighing and mixing an amorphous silicon nitride powder and/or a
nitrogen-containing silane compound, an AlN-containing substance
working out to an aluminum source, a nitride, oxynitride or oxide
of Li or a precursor substance capable of becoming an oxide of Li
by pyrolysis, and a nitride, oxynitride or oxide of Eu or a
precursor substance capable of becoming an oxide of Eu by
pyrolysis, to give a composition containing lithium in excess over
the composition of the Li-containing .alpha.-sialon-based phosphor
represented by formula (1), and firing the mixture at 1,400 to
1,800.degree. C. in a nitrogen-containing inert gas atmosphere
under atmospheric pressure.
13. A process for producing the phosphor of claim 9, comprising
mixing an amorphous silicon nitride powder and/or a
nitrogen-containing silane compound, an AlN-containing substance
working out to an aluminum source, a nitride, oxynitride or oxide
of Li or a precursor substance capable of becoming an oxide of Li
by pyrolysis, a nitride, oxynitride or oxide of Eu or a precursor
substance capable of becoming an oxide of Eu by pyrolysis, each in
a theoretical amount giving the composition of formula (1), and an
oxide of Li or a precursor substance capable of becoming an oxide
of Li by pyrolysis, in an amount in excess over said theoretical
amount, and firing the mixture at 1,500 to 1,800.degree. C. in a
nitrogen-containing inert gas atmosphere under atmospheric
pressure.
14. The process of claim 13, wherein the amount of metal lithium in
the oxide of Li or the precursor substance capable of becoming an
oxide of Li by pyrolysis, mixed in excess over said theoretical
amount, is from 0.1 to 1.25 mol per mol of the Li-containing
.alpha.-sialon-based phosphor as a product by a theoretical
amount.
15. A lighting device comprising a light emitting source and a
phosphor containing the phosphor claimed in claim 1.
16. The lighting device as claimed in claim 15, wherein said light
emitting source is an LED capable of emitting light at a wavelength
of 330 to 500 nm.
17. The lighting device as claimed in claim 16, wherein said
phosphor further contains a phosphor capable of emitting a red
color at 600 to 650 nm.
18. An image display device comprising an excitation source and a
phosphor containing the Li-containing .alpha.-sialon-based phosphor
claimed in claim 1.
19. A lighting device comprising a light emitting source and a
phosphor containing the phosphor claimed in claim 5.
20. A lighting device comprising a light emitting source and a
phosphor containing the phosphor claimed in claim 9.
Description
RELATED APPLICATIONS
[0001] This is a .sctn.371 of International Application No.
PCT/JP2009/064373, with an inter-national filing date of Aug. 11,
2009 (WO 2010/018873 A1, published Feb. 18, 2010), which is based
on Japanese Patent Application Nos. 2008-208569, filed Aug. 13,
2008, 2008-208570, filed Aug. 13, 2008, and 2009-048453, filed Mar.
2, 2009, the subject matter of which is incorporated by
reference.
TECHNICAL FIELD
[0002] This disclosure relates to an optical functional material
having a function of converting a part of irradiation light into
light at a different wavelength, and a production process thereof.
More specifically, this disclosure relates to a sialon-based
phosphor activated by a rare earth metal element, which is suitable
for an ultraviolet-to-blue light source. The disclosure also
relates to a production process of the sialon-based phosphor, and a
light emitting device and an image display device each using the
same.
BACKGROUND
[0003] Recently, with practical implementation of a blue
light-emitting diode (LED), development of a white LED utilizing
the blue LED is being aggressively sought. The white LED ensures
low power consumption and extended life compared with existing
white light sources, and therefore its application to liquid
crystal panel backlight, indoor or outdoor lighting device, and the
like is expanding.
[0004] The white LED developed at present is obtained by coating a
Ce-doped YAG (yttrium.aluminum.garnet) on a surface of a blue LED.
However, the Ce-doped YAG has a fluorescence wavelength in the
vicinity of 530 nm and when the color of this fluorescence and the
light of a blue LED are mixed to provide white light, blue-tinted
white light results and good white light cannot be obtained.
[0005] On the other hand, an .alpha.-sialon-based phosphor
activated by a rare earth element is known to emit fluorescence
with a longer wavelength than the fluorescence wavelength of
Ce-doped YAG (see Japanese Unexamined Patent Publication (Kokai)
No. 2002-363554). When a white LED is fabricated using fluorescence
of such sialon, a white LED giving a bulb color at a lower color
temperature than a white LED using YAG can be produced.
[0006] Also, in J. Phys. Chem., B2004, 108, 12027-12031, a
sialon-based phosphor having a compositional formula represented by
M.sub.xSi.sub.12--.sub.(m+n)Al.sub.m+nO.sub.nN.sub.16-n gives a
maximum intensity at m=2.8, and a peak wavelength in the vicinity
of 595 nm is obtained there. This fluorescence wavelength is
suitable for a white LED with a low color temperature as in a bulb
color, but a white LED with a high color temperature, such as
daytime white color or daylight color higher in the color
temperature, cannot be produced.
[0007] The daytime white color and daylight color have a wide range
of applications including not only lighting but also backlight of a
liquid crystal display device, etc., and their need is greater than
that for bulb color. To meet this need, fluorescence with a shorter
wave-length is required of the sialon-based phosphor. However, as
understood from J. Phys. Chem., B2004, 108, 12027-12031, a
Ca-containing .alpha. sialon phosphor is reduced in the
fluorescence intensity when the fluorescence wavelength is shifted
to the shorter wavelength side than 595 nm. Accordingly, it has
been difficult to produce a sialon-based phosphor capable of
emitting fluorescence at a short wavelength suitable for producing
a high-luminance LED of daytime white color or daylight color by
combining the phosphor with a blue LED.
[0008] To solve this problem, WO 2007/004493 A1 discloses a Li
(lithium)-containing .alpha.-sialon-based phosphor. This sialon can
emit fluorescence at a short wavelength compared with the
Ca-containing .alpha.-sialon-based phosphor. However, in the
disclosure above, the Li-containing .alpha.-sialon-based phosphor
is obtained in an atmosphere under nitrogen pressure of 1 MPa and
in view of a cumbersome production process or use of a production
apparatus capable of withstanding a high-temperature high-pressure
nitrogen gas, the phosphor is costly produce to. Also, x1
indicating the Li content in the above-described compositional
formula of sialon is an abnormally large value of
1.2.ltoreq.x1.ltoreq.2.4, and a Li-containing .alpha.-sialon-based
phosphor having a desired composition is difficult to produce with
good reproducibility.
[0009] As for the report on a Li-containing .alpha.-sialon-based
phosphor, Japanese Unexamined Patent Publication (Kokai) No.
2004-67837 is known in addition to WO '493, but the Li-containing
.alpha.-sialon-based phosphor disclosed has a fluorescence
wavelength of 585 nm and differs in the composition from the
Li-containing .alpha.-sialon-based phosphor. With such a
fluorescence wavelength, even when combined with a blue
light-emitting diode, an LED of daytime white color or daylight
color cannot be obtained.
[0010] Furthermore, in WO '493, the form or aggregation state of
particles is not considered. In WO '493, a Li-containing
.alpha.-sialon-based phosphor is produced using crystalline silicon
nitride. In the case of a Ca-containing .alpha.-sialon-based
phosphor, when crystalline silicon nitride is used, this forms a
secondary particle where small primary particles are strongly
aggregated (fused). Such a case is seen in FIGS. 1 to 8 of Japanese
Unexamined Patent Publication (Kokai) No. 2006-152069. It is
presumed that the same occurs in the case of a Li-containing
.alpha.-sialon-based phosphor.
[0011] The form or aggregation state of particles of a phosphor
powder affects light scattering, absorption and in turn,
fluorescence intensity and furthermore, also affects the slurry
properties when coating the phosphor. The slurry properties are an
important factor in the production process.
[0012] The effect on the fluorescence intensity is described below.
In a phosphor, irrespective of the size of a primary particles or
secondary particles, when the particle size is reduced to about a
submicron, light scattering is increased to lower the absorption
and the fluorescence intensity is decreased. To avoid this, a
method of producing large secondary particles by aggregating
submicron primary particles may be considered. However, when such
powder is pulverized or is subjected to various handlings, the
submicron primary particles fall off, as a result, it is difficult
to avoid the effect of the primary particles. Also, in the case of
a secondary particle formed by aggregating small primary particles,
fine irregularities are produced on the secondary particle surface,
and this is considered to result in light scattering and a decrease
in the fluorescence intensity.
[0013] In addition, when the aggregation to a secondary particle is
firm, strong pulverization is required and incorporation of
impurities from the pulverizer occurs. If a component participating
in light absorption is immixed even in a small amount, the
characteristics of the phosphor are greatly deteriorated, and
therefore strong pulverization is not preferred.
[0014] Furthermore, when the particle size grows to tens of micron
or more, this gives rise to color unevenness or the like at the
time of fabricating a product such as white LED, and products with
stable quality cannot be fabricated. On the other hand, to obtain a
high-quality phosphor, i.e., a phosphor having high fluorescence
intensity, a particle with high crystallinity is necessary. From
this viewpoint, the primary particle is preferably a large crystal.
The reason therefor is that when the crystal size is small, the
fluorescence intensity decreases due to surface defects.
[0015] Considering these conditions, a phosphor with good
characteristics is preferably a powder in which primary particles
are distributed in the range of 1 to 20 .mu.m without aggregation
and the powder is composed of particles having a larger size in
this particle size range.
[0016] In Japanese Unexamined Patent Publication (Kokai) Nos.
2002-363554 and 2006-321921, the primary particle size of
Ca-containing .alpha.-sialon phosphor is already known, but studies
on the primary particle of Li-containing .alpha.-sialon are not
sufficiently made in JP '337 and JP '921. Despite the disclosure of
JP '337 and JP '921, the growth of a primary particle of
Li-containing .alpha.-sialon cannot be estimated to be the same as
that of Ca-containing .alpha.-sialon, because Li is an easily
evaporable element or the substance related to Li may form a
compound having a relatively low melting point.
[0017] As regards the phosphor, a technique of using a flux is
widely employed as a technique for regulating the form of primary
particles. For growing a large primary particle, using a flux may
also be considered in the Li-containing .alpha.-sialon. In WO '493,
fluoride, chloride, iodide, bromide and phosphate of Li, Na, K, Mg,
Ca, Sr, Ba, Al and Eu, particularly, lithium fluoride, calcium
fluoride and aluminum fluoride, are pointed out as flux, but their
effects are not specifically described, and the technique disclosed
merely suggests a general technique.
[0018] It could therefore be helpful to provide a phosphor having
high fluorescence intensity and emitting a fluorescence color
making it possible to produce a white light-emitting diode of
daytime white color or daylight color by combining the phosphor
with a blue LED.
[0019] It could also be helpful to provide a Li-containing
.alpha.-sialon phosphor powder having high fluorescence intensity
and having excellent properties as a phosphor powder by controlling
the primary particle of Li-containing .alpha.-sialon. Such a
Li-containing .alpha.-sialon can produce a high-efficiency white
light-emitting diode of daytime white color or daylight color by
combining it with an ultraviolet-to-blue LED.
[0020] It could further be helpful to provide a lighting device
such as white LED of daytime white color or daylight color by
providing a Li-containing .alpha.-sialon-based phosphor having high
fluorescence intensity and using an ultraviolet or blue LED as a
light source.
[0021] It could yet further be helpful to achieve high luminance
and stable color tone of an image evaluation device having an
excitation source such as electron beam.
[0022] It could also be helpful to provide a novel production
process where a sialon-based phosphor capable of emitting the
above-described fluorescence color with high intensity can be
obtained in a high yield.
SUMMARY
[0023] We found that a Li-containing .alpha.-sialon-based phosphor
having a specific composition and being producible in an atmosphere
of nitrogen gas under atmospheric pressure can realize excellent
fluorescence intensity and short fluorescence wavelength.
[0024] We also found that when a nitrogen-containing silane
compound and/or an amorphous silicon nitride powder are used as
starting materials, a Li-containing .alpha.-sialon phosphor having
a large primary particle size, allowing for little aggregation of
primary particles with each other and exhibiting a weak cohesive
force can be obtained. Moreover, this phosphor has higher
fluorescence intensity than that produced using crystalline silicon
nitride.
[0025] We further found that in the case of an .alpha.-sialon-based
phosphor containing Li and Eu, a Li-containing .alpha.-sialon
having a large primary particle size can be obtained. We also found
that in this method, a Li-containing .alpha.-sialon-based phosphor
powder capable of emitting fluorescence at a shorter wavelength can
be obtained and the fluorescence intensity thereof is high as
compared with those produced by an ordinary method.
[0026] In this way, we provide the following.
[0027] An Li-containing .alpha.-sialon-based phosphor represented
by formula (1):
Li.sub.xEu.sub.ySi.sub.12-(m+n)Al.sub.(m+n)O.sub.n+.delta.N.sub.16-n-.de-
lta. (1)
(wherein assuming that the average valence of Eu is a,
x+ya+.delta.=m; 0.45.ltoreq.x<1.2, 0.001.ltoreq.y.ltoreq.0.2,
0.9.ltoreq.m.ltoreq.2.5, 0.5.ltoreq.n.ltoreq.2.4, and
.delta.>0).
[0028] Preferably, we provide the Li-containing
.alpha.-sialon-based phosphor above, wherein the .delta. is from
0.05 to 1.2 and the ratio x/m between x and m is from 0.4 to 0.9.
Furthermore, a preferred Li-containing .alpha.-sialon-based
phosphor above has x of 0.82.ltoreq.x<1.2 and the x/m of from
0.5 to 0.9.
[0029] In the Li-containing .alpha.-sialon-based phosphor, it is
preferred that the x is 0.91.ltoreq.x<1.2 and the x/m is from
0.6 to 0.9. Also, we provide the Li-containing .alpha.-sialon-based
phosphor above, wherein fluorescence having a peak wavelength of
560 to 580 nm is emitted by injecting excitation light.
[0030] A lighting device comprises a light emitting source and a
phosphor containing the Li-containing .alpha.-sialon-based phosphor
above. The light emitting source is preferably an LED capable of
emitting light at a wavelength of 330 to 500 nm. In one example of
the lighting device, the phosphor further contains a phosphor
capable of emitting a red color at 600 to 650 nm.
[0031] An image display device comprises an excitation source and a
phosphor containing the Li-containing .alpha.-sialon-based phosphor
above. In one example of the image display device, the excitation
source is an electron beam, an electric field, a vacuum
ultraviolet, or an ultraviolet ray.
[0032] A production process of the Li-containing
.alpha.-sialon-based phosphor above comprises weighing and mixing a
silicon nitride powder and/or a nitrogen-containing silane
compound, an AlN-containing substance working out to an aluminum
source, a nitride, oxynitride or oxide of Li or a precursor
substance capable of becoming an oxide of Li by pyrolysis, and a
nitride, oxynitride or oxide of Eu or a precursor substance capable
of becoming an oxide of Eu by pyrolysis, to give a composition
containing lithium in excess over the desired composition of the
Li-containing .alpha.-sialon-based phosphor represented by formula
(1), and firing the mixture at 1,400 to 1,800.degree. C. in a
nitrogen-containing inert gas atmosphere under atmospheric
pressure. In the production process of the Li-containing
.alpha.-sialon-based phosphor, the Li-containing
.alpha.-sialon-based phosphor after firing is preferably subjected
to acid washing.
[0033] A production process of the Li-containing
.alpha.-sialon-based phosphor is as above, wherein an amorphous
silicon nitride powder is used as the silicon nitride powder.
[0034] Preferably, the Li-containing .alpha.-sialon-based phosphor
powder is the Li-containing .alpha.-sialon-based phosphor
represented by formula (1), wherein the average aspect ratio of the
primary particle as measured by the image analysis of the scanning
electron micrograph is 2 or less and the average particle diameter
D.sub.particle is from 1 to 3.0 .mu.m.
[0035] Also, preferably, the Li-containing .alpha.-sialon-based
phosphor powder above has particles measured by the image analysis
of the scanning electron micrograph, a primary particle of 0.8
.mu.m or more is present in an area ratio of 70% or more.
Furthermore, the Li-containing .alpha.-sialon-based phosphor powder
above has a frequency distribution curve in the particle size
distribution curve measured by a laser diffraction/scattering
particle size distribution measuring apparatus is a single peak and
the median diameter is from 4 to 15 .mu.m.
[0036] Also, the Li-containing .alpha.-sialon-based phosphor powder
above has a 10% diameter in the particle size distribution curve of
1.5 .mu.m or more and the 90% diameter is 15 .mu.m or less.
[0037] Also, the Li-containing .alpha.-sialon-based phosphor powder
above has fluorescence having a peak wavelength of 560 to 580 nm is
emitted by injecting excitation light.
[0038] Also, a lighting device comprises a light emitting source
and a phosphor containing the Li-containing .alpha.-sialon-based
phosphor powder above. The light emitting source is preferably an
LED capable of emitting light at a wavelength of 330 to 500 nm. In
another example of the phosphor, the phosphor may contain a
phosphor capable of emitting a red color at 600 to 650 nm.
[0039] Also, a production process of the Li-containing
.alpha.-sialon-based phosphor powder above comprises weighing and
mixing an amorphous silicon nitride powder and/or a
nitrogen-containing silane compound, an AlN-containing substance
working out to an aluminum source, a nitride, oxynitride or oxide
of Li or a precursor substance capable of becoming an oxide of Li
by pyrolysis, a nitride, oxynitride or oxide of Eu or a precursor
substance capable of becoming an oxide of Eu by pyrolysis, to give
a composition containing lithium in excess over the desired
composition of the Li-containing .alpha.-sialon-based phosphor
represented by formula (1), and firing the mixture at 1,400 to
1,800.degree. C. in a nitrogen-containing inert gas atmosphere
under atmospheric pressure.
[0040] Preferably, a Li-containing .alpha.-sialon-based phosphor
particle is the Li-containing .alpha.-sialon-based phosphor
represented by formula (1), wherein the aspect ratio of the primary
particle as measured by the image analysis of the scanning electron
micrograph is 3 or less and the length of the short axis is more
than 3 .mu.m.
[0041] Furthermore, a production process of the Li-containing
.alpha.-sialon-based phosphor powder above comprises mixing an
amorphous silicon nitride powder and/or a nitrogen-containing
silane compound, an AlN-containing substance working out to an
aluminum source, a nitride, oxynitride or oxide of Li or a
precursor substance capable of becoming an oxide of Li by
pyrolysis, a nitride, oxynitride or oxide of Eu or a precursor
substance capable of becoming an oxide of Eu by pyrolysis, each in
a theoretical amount giving the composition of formula (1), and an
oxide of Li or a precursor substance capable of becoming an oxide
of Li by pyrolysis, in an amount higher than the theoretical
amount, and firing the mixture at 1,500 to 1,800.degree. C. in a
nitrogen-containing inert gas atmosphere under atmospheric
pressure.
[0042] The amount of metal lithium in the oxide of Li or the
precursor substance may be capable of becoming an oxide of Li by
pyrolysis, mixed in excess over the theoretical amount, is
preferably from 0.1 to 1.25 mol per mol of the Li-containing
.alpha.-sialon-based phosphor as a product by the theoretical
amount.
[0043] A lighting device comprises a light emitting source and a
phosphor containing the Li-containing .alpha.-sialon-based phosphor
represented by formula (1). The light emitting source is an LED
capable of emitting light at a wavelength of 330 to 500 nm.
[0044] The Li-containing .alpha.-sialon-based phosphor is designed
to have a specific composition by adjusting the Li content of the
product, whereby a lighting device such as white LED exhibiting
conventionally unobtainable high fluorescence intensity and
emitting a daytime white color or daylight color when using an
ultraviolet or blue LED as a light source can be provided.
[0045] Preferably, amorphous silicon nitride and/or a
nitrogen-containing silane compound is used as the starting
material to give a Li-containing .alpha.-sialon-based phosphor
particle having a specific particle form and the Li content of the
product is adjusted to give a Li-containing .alpha.-sialon-based
phosphor particle having a specific composition, whereby a phosphor
exhibiting conventionally unobtainable high fluorescence intensity
can be obtained.
[0046] Preferably, a Li-containing .alpha.-sialon phosphor having
an unprecedentedly large primary particle size can be obtained. The
Li-containing .alpha.-sialon phosphor exhibits high fluorescence
intensity and, at the same time, has excellent properties as a
phosphor powder.
[0047] Also, by using this phosphor powder, a high-luminance
lighting device such as white LED capable of emitting a daytime
white color or a daylight color when using an ultraviolet or blue
LED as a light source can be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0048] FIGS. 1A and 1B are SEM photographs showing the state in one
example of the powder after acid treatment in Example 2 and Example
6. FIG. 1A is an SEM photograph of a Li-containing
.alpha.-sialon-based phosphor powder produced using amorphous
silicon nitride as a raw material, and FIG. 1B is an SEM photograph
of a Li-containing .alpha.-sialon-based phosphor powder produced
using crystalline silicon nitride as a raw material.
[0049] FIGS. 2A and 2B are SEM photographs showing one example of
the phosphor powder after pulverization in Example 2 and Example 6.
FIG. 2A is an SEM photograph of a Li-containing
.alpha.-sialon-based phosphor powder produced using amorphous
silicon nitride as a raw material, and FIG. 2B is an SEM photograph
of a Li-containing .alpha.-sialon-based phosphor powder produced
using crystalline silicon nitride as a raw material.
[0050] FIGS. 3A and 3B are enlarged photographs of FIGS. 2A and
2B.
[0051] FIG. 4A is a particle size distribution (frequency
distribution curve) chart of the Li-.alpha.-sialon phosphor powder
obtained in Example 2, and FIG. 4B is a particle size distribution
chart of the phosphor powder obtained in Example 6 using
crystalline silicon nitride as a raw material.
[0052] FIG. 5 is an SEM photograph of the powder obtained in
Example 11.
DETAILED DESCRIPTION
[0053] Our disclosure is described in detail below.
[0054] The Li-containing .alpha.-sialon-based phosphor is
represented by formula (1):
Li.sub.xEu.sub.ySi.sub.12-(m+n)Al.sub.(m+n)O.sub.n+.delta.N.sub.16-n-.de-
lta. (1)
wherein assuming that the average valence of Eu is a,
x+ya+.delta.=m (provided that .delta.>0).
[0055] The Li-containing .alpha.-sialon-based phosphor is
characterized by the content of Li. That is, we found that the
Li-containing .alpha.-sialon-based phosphor obtained through firing
in a nitrogen-containing inert gas atmosphere under atmospheric
pressure has a great difference in the Li content between the
charge composition and the composition of the synthesis product
obtained. Li is an easily evaporable element and evaporation occurs
during firing, as a result, the Li content in the Li-containing
.alpha.-sialon-based phosphor obtained after acid washing becomes
small. Evaporation of Li is significant particularly when firing
under atmospheric pressure or under reduced pressure and by
investigating in detail the correlation between the charge
composition and the composition of the synthesis product obtained,
it has been found that when in the above-described compositional
formula of Li-containing .alpha.-sialon, 6 is from 0.05 to 1.2 and
the ratio x/m between x and m is from 0.4 to 0.9, a phosphor
identified as a substantially single-phase Li-containing
.alpha.-sialon-based phosphor by the X-ray diffraction pattern can
be obtained. We are the first to indicate that in the Li
compositional region of the Li-containing .alpha.-sialon-based
phosphor, both excellent fluorescence intensity and shorter
fluorescence wavelength can be achieved.
[0056] The Li-containing .alpha.-sialon-based phosphor is
synthesized by performing acid washing after firing at 1,400 to
2,000.degree. C. in an inert gas atmosphere under a pressure of
0.08 to 0.9 MPa. As for the firing atmosphere, the firing is
preferably carried in a nitrogen atmosphere under atmospheric
pressure. In particular, the production cost of the Li-containing
.alpha.-sialon-based phosphor can be reduced by performing the
synthesis in a nitrogen-containing inert gas atmosphere under
atmospheric pressure. We synthesized Li-containing
.alpha.-sialon-based phosphors having various compositions in a
nitrogen atmosphere under atmospheric pressure and discovered
compositional features with respect to fluorescence characteristics
of the Li-containing .alpha.-sialon-based phosphor obtained after
acid washing. As a result, a Li-containing .alpha.-sialon-based
phosphor satisfying both excellent fluorescence intensity and
shorter fluorescence wavelength can be synthesized for the first
time by firing in a nitrogen atmosphere under atmospheric
pressure.
[0057] Furthermore, the Li-containing .alpha.-sialon-based phosphor
is characterized, as described above, in that x+ya+.delta.=m
(provided that .delta.>0) and x+ya is smaller than m. a is the
average valence of Eu, but the valence of Eu varies depending on
the temperature and the oxygen partial pressure in the atmosphere.
It is considered that trivalent Eu is stable at room temperature
and only Eu.sub.2O.sub.3 is known as an oxide thereof, but when the
temperature rises, rather divalent Eu becomes stable and Eu is
reduced to divalent Eu at high temperature in a nitrogen atmosphere
and solid-dissolved as Eu.sup.2+ in the crystal lattice of
.alpha.-sialon. As disclosed in paragraph 0065 at page 14 of WO
'493, in all of documents and patent publications heretofore
reported, the compositional formula of .alpha.-sialon is composed
by regarding Eu as divalent. Accordingly, in the composition of the
Li-containing .alpha.-sialon, .delta. is calculated on the
condition that the valence of Eu is divalence.
[0058] The amount of metal solid-dissolved is m/[valence of metal]
in all conventional sialons and the Li-containing
.alpha.-sialon-based phosphor compositions in conventional
techniques all satisfy the relational expression of x+ya=m. On the
other hand, the Li-containing .alpha.-sialon-based phosphor is
characterized in that the content of Al is larger than in the
conventional composition and the chemical composition is
represented by formula (1). As a result of the condition that x+ya
is smaller than m, the ratio between Si atom and Al atom
constituting the Li-containing .alpha.-sialon-based phosphor varies
and, at the same time, the proportion of oxygen atom and the
proportion of nitrogen atom are varied.
[0059] Due to compositional change of constituent atoms in such a
Li-containing .alpha.-sialon-based phosphor, charge shift may be
caused. In this case, the charge balance may be compensated for by
a defect produced in the Li-containing .alpha.-sialon-based
phosphor. In the crystal lattice of .alpha.-sialon, a network
composed of cation (Si, Al)-anion (O, N)-cation (Si, Al)-anion (O,
N)- is present and a metal element such as Li and Eu intrudes and
exists as a solid solution in gaps in the network. When a vacancy
is produced on the cation site, the proportion of oxygen or
nitrogen atom on the anion site is relatively increased, whereas
when a vacancy is produced on the anion site, the proportion of
oxygen or nitrogen atom on the anion site is relatively decreased.
Therefore, the chemical composition is more generally represented
by the following formula (2):
Li.sub.xEu.sub.ySi.sub.12-(m+n)Al.sub.(m+n)O.sub.n+.epsilon.N.sub.16-n-.-
phi. (2)
wherein assuming that the average valence of Eu is a,
x+ya+.delta.=m and .delta.=3.phi.-2.epsilon. and wherein
(n+.epsilon.) indicates the number of oxygen atoms occupying the
anion site and (16-n-.phi.) indicates the number of nitrogen atoms
occupying the anion site, provided that .delta.>0,
-.delta./2.ltoreq..epsilon..ltoreq..delta./2, and
-.delta./3.ltoreq..phi..ltoreq..delta./3.
[0060] When it is tried to synthesize sialon with x+ya being equal
to m by increasing Li in raw materials, production of a heterophase
occurs and a single-phase Li-containing .alpha.-sialon-based
phosphor cannot be obtained. The Li-containing .alpha.-sialon-based
phosphor produced by the process is obtained based on the finding
that stable sialon results when x+ya is not equal to m. Focusing on
equalizing x+ya with m leads to a rise in cost such as synthesis in
a high-pressure nitrogen gas and also disadvantageously suffers
from poor reproducibility.
[0061] The compositional range giving a single-phase Li-containing
.alpha.-sialon-based phosphor is, in formula (1) of a Li-containing
.alpha.-sialon-based phosphor, 0.45.ltoreq.x<1.2, preferably
0.82.ltoreq.x<1.2, more preferably 0.91.ltoreq.x<1.2. If x is
less than 0.45, the fluorescence intensity deceases, whereas if it
is 1.2 or more, a heterophase is produced and a single-phase
.alpha.-sialon-based phosphor cannot be obtained. In particular,
the compositional range satisfying both short wavelength and
fluorescence intensity is 0.82.ltoreq.x<1.2. The wavelength of
fluorescence shifts to short wavelength with an increase in the Li
content and can be varied in the range of, in terms of peak
wavelength, from 560 to 580 nm.
[0062] Also, the Li-containing .alpha.-sialon-based phosphor is
characterized by .delta.>0 and, particularly, when .delta. is
from 0.05 to 1.2 and the ratio x/m between x and m is from 0.5 to
0.9, this is preferred because high fluorescence intensity is
obtained. It is more preferred that .delta. is from 0.05 to 1.0 and
the x/m ratio is from 0.6 to 0.9.
[0063] Eu is an element which is solid-dissolved in the
Li-containing .alpha.-sialon-based phosphor and works out to a
light emitting source and, in formula (1), y is preferably
0.001.ltoreq.y.ltoreq.0.2. If y is less than 0.001, the content of
the light emitting source is reduced and a bright phosphor cannot
be obtained. Also, if it exceeds 0.2, a sialon emitting
fluorescence at a short wavelength cannot be obtained. A preferred
range is 0.01.ltoreq.y.ltoreq.0.15, and a more preferred range is
0.01.ltoreq.y.ltoreq.0.1.
[0064] m and n are 0.9.ltoreq.m.ltoreq.2.5 and
0.5.ltoreq.n.ltoreq.2.4. m is a value determined so as to keep
electrical neutrality when a metal element is solid-dissolved in
sialon, and m=x+ya+.delta.. a is the average valence of Eu. The
number of Al atoms substituted for Si atom excessively over the
number of Al atoms substituted on the cation site corresponding to
the number of metal elements (Li and Eu) intruded and existing as a
solid solution in the network composed of cation (Si, Al)-anion (O,
N)-cation (Si, Al)-anion (O, N)-constituting .alpha.-sialon is
denoted as .delta. (in this disclosure, .delta.>0). If m is less
than 0.9, the sialon crystal is hardly stabilized due to the small
solid solution amount of metal elements (Li and Eu) and the
fluorescence intensity of the phosphor may decrease, whereas if the
m value exceeds 2.5, a crystal phase other than sialon is readily
produced. m is preferably 0.9.ltoreq.m.ltoreq.2.5. n is the value
related to the substitution solid-solution amount of oxygen in the
Li-containing .alpha.-sialon-based phosphor. If the n value is less
than 0.5 or (n+.delta.) is less than 0.55, the sialon crystal is
hardly stabilized due to the small solid solution amount of metal
elements (Li and Eu) and the fluorescence intensity may decrease,
whereas if the n value exceeds 2.4 or (n+.delta.) exceeds 3.2, a
crystal phase other than sialon is readily produced. Preferred
ranges are 1.0.ltoreq.m.ltoreq.2.1, 1.4.ltoreq.n.ltoreq.2.4 and
1.8.ltoreq.n+.delta..ltoreq.3.1, and more preferred ranges are
1.1.ltoreq.m.ltoreq.2.0, 1.55.ltoreq.n.ltoreq.2.3 and
1.9.ltoreq.n+.delta..ltoreq.3.0.
[0065] The term "heterophase" as used herein is a heterophase
identified by the diffraction pattern of X-ray diffraction and
excludes a component not appearing in the X-ray diffraction, such
as glass.
[0066] The production process of the sialon-based phosphor powder
is described below.
[0067] The Li-containing .alpha.-sialon-based phosphor powder can
be obtained by weighing and mixing a silicon nitride powder, an
AlN-containing substance working out to an aluminum source, a
nitride, oxynitride or oxide of Li or a precursor substance capable
of becoming an oxide of Li by pyrolysis, and a nitride, oxynitride
or oxide of Eu or a precursor substance capable of becoming an
oxide of Eu by pyrolysis, to give a composition containing lithium
in excess over the desired composition of the Li-containing
.alpha.-sialon-based phosphor, and firing the mixture at 1,400 to
2,000.degree. C. in a nitrogen-containing inert gas atmosphere
under atmospheric pressure. The obtained powder is washed with an
acid solution to remove a glass component and the like attached to
the surface, whereby a phosphor powder composed of substantially a
single phase of Li-containing .alpha.-sialon-based phosphor can be
finally obtained.
[0068] The amount of the Li compound as a raw material is increased
so as to prevent the Li content of the obtained Li-containing
.alpha.-sialon-based phosphor from becoming too small, because Li
readily evaporates.
[0069] As the raw material silicon nitride powder, amorphous
silicon nitride or a nitrogen-containing silane compound and/or an
amorphous silicon nitride powder may be used.
[0070] Examples of the nitrogen-containing silane compound which
can be used include silicon diimide (Si(NH).sub.2) and silicon
nitrogen imide (Si.sub.2N.sub.2NH). Also, such a compound may be
used by mixing it with a silicon nitride powder.
[0071] The nitrogen-containing silane compound and/or amorphous
silicon nitride compound, which are a main raw material, can be
obtained by a known method, for example, by decomposing an
Si--N--H-based precursor compound such as silicon diimide produced
through the reaction of a silicon halide such as silicon
tetrachloride, silicon tetrabromide and silicon tetraiodide with
ammonia in a gas phase or liquid phase state, under heating at 600
to 1,200.degree. C. in a nitrogen or ammonia gas atmosphere. The
crystalline silicon nitride powder can be obtained by firing the
obtained nitrogen silane compound and/or amorphous silicon nitride
powder at 1,300 to 1,550.degree. C. The crystalline silicon nitride
can also be obtained by directly nitriding a metal silicon in a
nitrogen atmosphere, but this method requires a pulverization step
to obtain a fine powder and, therefore, readily allows for mingling
of impurities. For this reason, a method of decomposing a
precursor, where a high-purity powder can be easily obtained, is
preferably employed.
[0072] As for the nitrogen-containing silane compound and/or
amorphous silicon nitride powder and the crystalline silicon
nitride powder, a material having an oxygen content of 1 to 5 mass
% is used. A material having an oxygen content of 1 to 3 mass % is
preferred. If the oxygen content is less than 1 mass %, it becomes
very difficult to produce an .alpha.-sialon phase by the reaction
in the firing process and remaining of a crystal phase of the
starting material or production of AlN polytypes such as 21R is
disadvantageously liable to occur, whereas if the oxygen content
exceeds 5 mass %, the proportion of .beta.-sialon or oxynitride
glass produced increases, though the .alpha.-sialon production
reaction is accelerated.
[0073] Also, as for the nitrogen-containing silane compound and/or
amorphous silicon nitride powder, a material having a specific
surface area of 80 to 600 m.sup.2/g is preferably used. A material
having a specific surface area of 340 to 500 m.sup.2/g is more
preferred. In the case of crystalline silicon nitride, a raw
material having a specific surface area of 1 to 15 m.sup.2/g is
preferably used.
[0074] The substance working out to the aluminum source includes
aluminum oxide, metal aluminum and aluminum nitride, and these
powders each may be used alone or may be used in combination. As
for the aluminum nitride powder, a general powder having an oxygen
content of 0.1 to 8 mass % and a specific surface area of 1 to 100
m.sup.2/g can be used.
[0075] The precursor substance capable of becoming an oxide of Li
or Eu includes respective metal salts such as carbonate, oxalate,
citrate, basic carbonate and hydroxide.
[0076] The amount of metal impurities other than the constituent
components of the Li-containing .alpha.-sialon-based phosphor is
preferably 0.01 mass % or less. In particular, as for the
nitrogen-containing silane compound and/or amorphous silicon
nitride powder, and/or the crystalline silicon nitride, which are
added in a large amount, as well as aluminum oxide and AN, the
content of metal impurities in the material used is 0.01 mass % or
less, preferably 0.005 mass % or less, more preferably 0.001 mass
%. As for the oxide of metal Li or the precursor substance capable
of becoming an oxide of Li by pyrolysis and the oxide of metal Eu
or the precursor capable of becoming an oxide of Eu by pyrolysis,
use of a material giving an oxide having a metal impurity content
of 0.01 mass % or less is also preferred.
[0077] The method for mixing respective starting materials
described above is not particularly limited, and a known method,
for example, a method of dry mixing the materials, and a method of
wet mixing the materials in an inert solvent which is substantially
incapable of reacting with respective components of the raw
material, and then removing the solvent, may be employed. A mixing
device such as a V-type mixer, rocking mixer, ball mill, vibration
mill and medium stirring mill may be used. However, the
nitrogen-containing silane compound and/or amorphous silicon
nitride powders are highly sensitive to moisture and humidity and,
therefore, the mixing of starting materials must be performed in a
controlled inert gas atmosphere.
[0078] The mixture of starting materials is fired at 1,400 to
1,800.degree. C., preferably at 1,500 to 1,700.degree. C., in a
nitrogen-containing inert gas atmosphere under atmosphere pressure
to obtain the desired Li-containing .alpha.-sialon-based phosphor
powder. Examples of the inert gas include helium, argon, neon and
krypton, but such a gas may also be used by mixing it with a small
amount of hydrogen gas. If the firing temperature is less than
1,400.degree. C., an impracticably long period of heating is
required for the production of the desired Li-containing
.alpha.-sialon-based phosphor powder, and the proportion of
Li-containing .alpha.-sialon-based phosphor phase in the powder
produced is also reduced. If the firing temperature exceeds
1,800.degree. C., there arises an undesirable problem that silicon
nitride and sialon are sublimated and decomposed to produce free
silicon.
[0079] The heating furnace used for firing of the powder mixture is
not particularly limited and, for example, a high-frequency
induction heating- or resistance heating-system batch-type electric
furnace, a rotary kiln, a fluidizing firing furnace and a
pusher-type electric furnace may be used. As for the firing
crucible, a BN-made crucible, a silicon nitride-made crucible, a
graphite-made crucible and a silicon carbide-made crucible may be
used. In the case of a graphite-made crucible, the inner wall is
preferably coated with silicon nitride, boron nitride and the
like.
[0080] In the thus-obtained Li-containing .alpha.-sialon-based
phosphor, a glass layer is attached to the surface and for
obtaining a phosphor having a higher fluorescence intensity, the
glass layer is preferably removed. The easiest way to remove the
glass layer on the phosphor particle surface is washing with an
acid, i.e., a treatment of placing the sialon particle in the
solution of an acid selected from sulfuric acid, hydrochloric acid
and nitric acid and removing the glass layer on the surface. The
concentration of the acid solution is from 0.1 to 7 N, preferably
from 1 to 3 N. If the concentration is excessively high, oxidation
aggressively proceeds and good fluorescence characteristics cannot
be obtained. In an acid solution whose concentration is adjusted,
the sialon-based phosphor powder is placed in an amount of 5 wt %
based on the solution and kept for a desired time with stirring.
After the washing, the solution containing the sialon-based
phosphor powder is filtered, washed with water to flush out the
acid, and dried.
[0081] Preferably, the Li-containing .alpha.-sialon phosphor is
characterized by the size and crystal form of the particle
constituting the phosphor, in addition to the above-described
compositional features.
[0082] The Li-containing .alpha.-sialon-based phosphor powder may
have a compositional feature of having the above-described Li
content and a feature of producing the phosphor powder by using an
amorphous silicon nitride powder and a nitrogen-containing silane
compound as raw materials and is obtained by weighing and mixing an
amorphous silicon nitride powder and/or a nitrogen-containing
silane compound, an Al source, a Li source and a Eu source to give
a composition containing lithium in excess over the desired
composition of the Li-containing .alpha.-sialon-based phosphor
represented by formula (1), and firing the mixture in a
nitrogen-containing inert gas atmosphere under atmospheric
pressure.
[0083] Due to use of an amorphous silicon nitride powder and a
nitrogen-containing silane compound as raw materials, the
Li-containing .alpha.-sialon-based phosphor powder may come to have
the below-described characteristic form and aggregation state of
particles. FIGS. 1A and 1B are scanning electron microscope (SEM)
photographs showing the state of the powder after acid treatment of
the Li-containing .alpha.-sialon-based phosphor particles obtained
in Example 2 and Example 6 according to this example, where a part
of secondary particles each formed by fusion/aggregation of primary
particles is being observed. FIG. 1A is an SEM photograph of
Li-containing .alpha.-sialon-based phosphor particles using
amorphous silicon nitride as a raw material, and FIG. 1B is an SEM
photograph of Li-containing .alpha.-sialon-based phosphor particles
using crystalline silicon nitride as a raw material. In FIG. 1A, it
is seen that the phosphor is composed of particles of 1 to 2 .mu.m.
These are an automorphic primary particle of the Li-containing
.alpha.-sialon-based phosphor particle. In FIG. 1B, it is seen that
the phosphor is composed of particles of 0.5 to 1.3 .mu.m. This
particle is a secondary particle resulting from aggregation of
several Li-containing .alpha.-sialon-based phosphor particle
crystals, and a crystal exhibiting automorphism is scarcely
observed.
[0084] FIGS. 2A, 2B, 3A and 3B are SEM photographs showing
representative examples when the particles above are pulverized
into a state usable as a phosphor powder. FIG. 2A is an SEM
photograph of a Li-containing .alpha.-sialon-based phosphor powder
produced using amorphous silicon nitride as a raw material, and
FIG. 2B is an SEM photograph of a Li-containing
.alpha.-sialon-based phosphor powder produced using crystalline
silicon nitride as a raw material. FIGS. 3A and 3B are enlarged
photographs of FIGS. 2A and 2B. In FIG. 2A which is a Li-containing
.alpha.-sialon-based phosphor powder produced using amorphous
silicon nitride as a raw material, a large number of six-sided
prismatic or six-sided pyramidal primary particles having a
particle size of 1 to 1.5 .mu.m are present and fine particles are
scarcely observed. The size of the primary particle diameter varies
depending on the composition and the firing conditions, but the
results of image analysis of the SEM photograph reveal that in our
range, the average particle diameter D.sub.particle is from 1.0 to
3.0 .mu.m. Production of a particle having an average particle
diameter larger than the range above requires an extremely long
time for the firing process and this is not practical. Also, an
average particle diameter of 0.5 .mu.m or less has no difference
from that of particles produced using a crystalline material.
Furthermore, as seen also from the SEM photographs, the aspect
ratio of particles constituting the Li-containing
.alpha.-sialon-based phosphor powder is 2 or less. FIG. 2B is an
SEM photograph of a Li-containing .alpha.-sialon-based phosphor
particle using crystalline silicon nitride as a raw material.
[0085] The Li-containing .alpha.-sialon-based phosphor powder in
this example is characterized by a large primary particle and
allows for little fusion/aggregation of primary particles with each
other. However, all particles are not so, and production of a small
particle also occurs. Preferably, as a result of measurement, the
existence area of particles of 0.8 .mu.m or more was 70% or more
based on the total area of all particles in the measurement range.
As this area is larger, the phosphor is better and as the area is
smaller, reduction in the fluorescence intensity may occur.
[0086] In FIG. 2B which is a powder using crystalline silicon
nitride as a raw material, an automorphic primary particle is not
present. As seen from FIG. 3B, a particle having a size of 1 to 1.3
.mu.m is a particle resulting from primary particles of about 0.5
.mu.m being tightly fused. Also, many crystals of fine particle of
0.5 .mu.m or less are present. In such powder, light scattering due
to a small particle is increased and the fluorescence intensity
decreases.
[0087] The difference in the existence mode between particles shown
in FIGS. 2A and 2B appears as the difference in the particle size
distribution. FIG. 4A shows a particle size distribution (frequency
distribution curve) of the Li-containing .alpha.-sialon phosphor
powder measured by a laser diffraction/scattering particle size
distribution measuring apparatus, and FIG. 4B shows a particle size
distribution when using crystalline silicon nitride. This frequency
distribution curve is drawn by evenly dividing the zones of
sufficiently large particle (about 1,000 .mu.m) and sufficiently
small particle (about 0.02 .mu.m) into 80 sections with a log-scale
and determining the frequency on a particle volume basis. In FIG.
4A, a particle size distribution having a single peak with the peak
appearing in the vicinity of 5 .mu.m is shown. Such a particle size
distribution is very preferred as a phosphor. The Li-containing
.alpha.-sialon-based phosphor powder may be weak in the
fusion/aggregation and, therefore, a powder having a median
diameter of 4 to 15 .mu.m and showing a single peak can be obtained
by weak pulverization. The shape of the single peak is important,
because the median diameter can be varied by the degree of
pulverization but the peak shape is dependent on the primary
particle size in the secondary particle.
[0088] On the other hand, in the case of using crystalline silicon
nitride as a raw material, the particle size distribution gives a
particle size distribution curve having two peaks at 1.5 .mu.m and
15 .mu.m, revealing that when amorphous silicon nitride is used as
a raw material, the properties of the powder obtained are more
excellent. As seen from FIG. 3B, in this case, small primary
particles are aggregated to form a secondary particle, and it is
considered that the powder is resulting from breakage of this
particle and, therefore, has the above-described two peaks.
[0089] The cause of producing a difference in the form and
aggregation state of particles between using amorphous silicon
nitride and/or nitrogen-containing silane compound and using
crystalline silicon nitride for the raw material is described
below.
[0090] The nucleation and growth of a Li-containing
.alpha.-sialon-based phosphor particle are thought to occur in a
glass phase of Li--Al--Si--O--N system produced in raw materials in
the course of temperature rising. The amorphous silicon nitride or
nitrogen-containing silane compound is an ultrafine powder having a
particle diameter of approximately from several nm to 10 nm and is
very bulky. Since this is a main component, it is believed that
other components can be uniformly dispersed therein and a fine
glass phase is uniformly formed at a low temperature. The
components of the Li-containing .alpha.-sialon-based phosphor are
considered to dissolve in the glass phase, allowing the nucleation
and growth to proceed stepwise and, in turn, enabling growth of a
Li-containing .alpha.-sialon-based phosphor particle having a large
particle diameter and exhibiting automorphism. Combined with high
bulkiness, each particle independently grows and, therefore,
fusion/aggregation scarcely takes place.
[0091] On the other hand, the crystalline silicon nitride, even a
fine particle, has a particle diameter of about 0.2 .mu.m and
compared with the amorphous silicon nitride or nitrogen-containing
silane compound, the particle size is very large. Therefore,
uniform contact with Li, Al, O and N forming a glass phase cannot
be ensured and in turn, a glass phase is thought to be produced
locally. Also, the number of glass particles produced is estimated
to be small. Since the particle diameter of existing silicon
nitride is large, the raw material does not dissolve in the glass
phase but the reaction to a Li-containing .alpha.-sialon-based
phosphor proceeds allowing glass to be present by covering the
silicon nitride particle surface. In such an existence mode of
glass phase, a glass phase is shared by a large number of crystal
nuclei and the growth proceeds competitively or simultaneously. As
a result, a secondary particle in which primary particles are
strongly fused/aggregated with each other is considered to be
formed.
[0092] A preferred production process of the Li-containing
.alpha.-sialon-based phosphor powder is described below. The
Li-containing .alpha.-sialon-based phosphor powder can be obtained
by weighing and mixing an amorphous silicon nitride powder and/or a
nitrogen-containing silane compound, an AlN-containing substance
working out to an aluminum source, a nitride, oxynitride or oxide
of Li or a precursor substance capable of becoming an oxide of Li
by pyrolysis, and a nitride, oxynitride or oxide of Eu or a
precursor substance capable of becoming an oxide of Eu by
pyrolysis, to give a composition containing lithium in excess over
the desired composition of the Li-containing .alpha.-sialon-based
phosphor, and firing the mixture at 1,400 to 2,000.degree. C. in a
nitrogen-containing inert gas atmosphere under atmospheric
pressure. The obtained powder is washed with an acid solution to
remove a glass component and the like attached to the surface,
whereby a phosphor powder composed of substantially a Li-containing
.alpha.-sialon-based phosphor can be finally obtained.
[0093] The production process of the Li-containing
.alpha.-sialon-based phosphor powder may be the same as the
above-described production process of the Li-containing
.alpha.-sialon-based phosphor powder except for using, as the
silicon nitride powder, an amorphous silicon nitride powder and/or
a nitrogen-containing silane compound instead of a crystalline
silicon powder.
[0094] Examples of the raw material nitrogen-containing silane
compound which can be used include silicon diimide (Si(NH).sub.2)
and silicon nitrogen imide (Si.sub.2N.sub.2NH). Also, a mixture of
a nitrogen-containing silane compound and an amorphous silicon
nitride powder may be used.
[0095] The Li-containing .alpha.-sialon-based phosphor particle may
preferably be a Li-containing .alpha.-sialon-based phosphor having
a composition represented by formula (1), wherein the aspect ratio
of the primary particle as measured by the image analysis of the
scanning electron micrograph is 3 or less and the length of the
short axis is more than 3 .mu.m. The upper limit of the short axis
length is preferably 5 .mu.m. Such a Li-containing
.alpha.-sialon-based phosphor particle has high fluorescence
intensity.
[0096] The Li-containing .alpha.-sialon-based phosphor powder may
be characterized in that an .alpha.-sialon composition having the
above-described Li content is employed, an amorphous silicon
nitride powder and/or a nitrogen-containing silane compound are
used as raw materials, and lithium oxide and/or a raw material
capable of forming lithium oxide at a high temperature are added in
excess at the production, and this powder can be obtained by
weighing an amorphous silicon nitride powder and/or a
nitrogen-containing silane compound, an Al source, a Li source and
a Eu source to give the desired composition of the Li-containing
.alpha.-sialon-based phosphor represented by formula (1), further
adding and mixing an excess of Li oxide or precursor substance
capable of becoming an oxide of Li by pyrolysis to the powder
above, and firing the mixture in a nitrogen-containing inert gas
atmosphere.
[0097] FIG. 5 is a scanning electron microscope (SEM) photograph
showing the state of powder after acid treatment of the
Li-containing .alpha.-sialon-based phosphor particle obtained in
Example 11. A part of secondary particles each formed by weakly
fused primary particles is being observed.
[0098] FIG. 5 is a Li-containing .alpha.-sialon-based phosphor
particle produced using raw materials where an oxide of Li or a
precursor substance capable of becoming an oxide of Li by pyrolysis
is added in excess to amorphous silicon nitride.
[0099] In FIG. 5, the form (automorphism) of the primary particle
of Li-containing .alpha.-sialon-based phosphor can be distinctly
confirmed. This powder contains a particle where the short axis of
the primary particle is more than 3 .mu.m.
[0100] The cause of producing a difference in the form and
aggregation state of primary particles shown in FIG. 5 is described
below. The nucleation and growth of a Li-containing
.alpha.-sialon-based phosphor particle are thought to occur in a
glass phase of Li--Al--Si--O--N system produced in raw materials in
the course of temperature rising.
[0101] First, the reason for difference in the size of the primary
particle is described below. In the case of using amorphous silicon
nitride and/or a nitrogen-containing silane compound and not using
an excess of lithium oxide, the size of the primary particle is
small. On the other hand, in the case of using an excess of lithium
oxide, the size of the primary particle is increased. This is
attributable to a difference in the amount of glass phase. That is,
when an excess of lithium oxide is used, the glass phase produced
is increased. When the glass phase is increased, the degree of
oversaturation of sialon in glass lowers and the amount of nuclei
produced is decreased. In turn, the amount of raw materials
supplied to one nucleus is increased, and the crystal size becomes
large.
[0102] Next, the aggregation state of particles is described,
although this is also described above. In the case of producing the
phosphor powder by using crystalline silicon nitride, aggregation
of the obtained phosphor powder aggressively occurs. On the other
hand, when amorphous silicon nitride and/or a nitrogen-containing
silane compound are used, the aggregation is reduced.
[0103] The amorphous silicon nitride and/or nitrogen-containing
silane compound are an ultrafine powder having a particle diameter
of approximately from several nm to 10 nm and, since this becomes a
main raw material of sialon, the raw materials of sialon using
amorphous silicon nitride is very bulky. In this powder, other raw
materials are uniformly dispersed and come into contact with the
ultrafine silicon nitride raw material. For this reason, a fine
glass phase is considered to be uniformly formed at a low
temperature. Moreover, due to bulkiness, the raw materials are in a
state of being spatially separated and when nucleation and growth
occur in such a glass phase, a powder reduced in aggregation
results.
[0104] On the other hand, in the case of crystalline silicon
nitride, the particle diameter is very large compared with the
amorphous silicon nitride and/or nitrogen-containing silane
compound and is about 0.2 .mu.m. Since silicon nitride is large,
the raw material does not dissolve in the glass phase and the
reaction to sialon is considered to proceed in such a manner that
glass covers the silicon nitride particle surface. Also, the bulk
of the sialon raw material using crystalline silicon nitride is
small and the glass phase cannot sufficiently enjoy spatial
isolation unlike using amorphous silicon nitride and/or
nitrogen-containing compound. If the reaction to sialon proceeds in
such a state, a secondary particle in which primary particles are
strongly fused/aggregated with each other is formed.
[0105] Lithium oxide added in excess and the raw material capable
of producing lithium oxide at a high temperature may fulfill a role
as a kind of flux but greatly differs from a general flux added for
the purpose of making the crystal form uniform. The following two
points are the reasons therefor. [0106] (1) In the synthesis of the
Li-containing .alpha.-sialon under atmospheric pressure,
evaporation of Li may be increased. If the sialon is produced
without replenishing Li, a Li-containing .alpha.-sialon largely
lacking in lithium results. Such a sialon has many defects and is
not preferred as a phosphor. To solve this problem, lithium oxide
or a raw material capable of forming lithium oxide at a high
temperature is added, whereby the lacking Li can be compensated
for. [0107] (2) An important feature of the Li-containing
.alpha.-sialon-based phosphor is to emit fluorescence at a short
wavelength as compared with the Ca-containing .alpha.-sialon-based
phosphor. It has been also revealed by the studies this time that
lithium oxide or a raw material capable of forming lithium oxide at
a high temperature is effective for the short fluorescence
wavelength above. This effect is considered to be brought about by
the supply of oxygen from the added reagent.
[0108] As described above, lithium oxide and a raw material capable
of producing lithium oxide at a high temperature may have an effect
of substantially enhancing the fluorescence characteristics of the
Li-containing .alpha.-sialon unlike a normal flux for merely
controlling the primary particle morphology of the crystal.
[0109] Generally, in the case of producing a sialon phosphor, it is
not preferred to use lithium oxide or a raw material capable of
forming lithium oxide at a high temperature for the flux. The flux
becomes an unnecessary component after obtaining a phosphor and is
preferably removed after the synthesis. For this reason, a
substance easily removable with water or an acid is usually
selected. Considering this point, a halogen compound such as barium
fluoride is selected. Lithium oxide is a hardly soluble component
compared with a halogen compound and is difficult to remove after
the synthesis and, therefore, this raw material is normally
unemployable as a flux. Then, we used a fluoride as a flux, but use
of a fluoride failed in producing a Li-containing
.alpha.-sialon-based phosphor composed of primary particles with
good morphology.
[0110] Moreover, the fluorescence intensity is reduced compared to
adding lithium oxide or a raw material capable of forming lithium
oxide at a high temperature. This is considered because evaporation
of Li cannot be compensated for. From these studies, it has been
concluded that only lithium oxide or a raw material capable of
forming lithium oxide at a high temperature is suitable as a flux
effective for the Li-containing .alpha.-sialon-based phosphor.
[0111] The method of adding lithium oxide or a raw material capable
of forming lithium oxide at a high temperature is believed to be
effective for all compositions of the Li-containing .alpha.-sialon,
and the composition of the Li-containing .alpha.-sialon-based
phosphor can be the above-described compositions.
[0112] The amount of lithium oxide or a raw material capable of
forming lithium oxide at a high temperature added in excess over
the Li-containing .alpha.-sialon-based phosphor powder raw material
(i.e., the theoretical amount of lithium oxide to give
Li-containing .alpha.-sialon to be produced) is, in terms of the
metal Li amount, preferably from 0.1 to 1.25 mol per mol of the
Li-containing .alpha.-sialon produced. If the amount added is less
than 0.1 mol, the effect of increasing the crystal size cannot be
sufficiently obtained, whereas if it exceeds 1.25 mol, the
production of heterophase is increased to cause reduction in the
fluorescence intensity. The amount added is more preferably from
0.15 to 0.8 mol.
[0113] A production process of the Li-containing
.alpha.-sialon-based phosphor powder is described below. The
Li-containing .alpha.-sialon-based phosphor powder can be obtained
by weighing an amorphous silicon nitride powder and/or a
nitrogen-containing silane compound, an AlN-containing substance
working out to an aluminum source, a nitride, oxynitride or oxide
of Li or a precursor substance capable of becoming an oxide of Li
by pyrolysis, and a nitride, oxynitride or oxide of Eu or a
precursor substance capable of becoming an oxide of Eu by
pyrolysis, to give the desired Li-containing .alpha.-sialon,
further adding and mixing an excess of Li oxide and/or an excess of
a precursor substance capable of becoming an oxide of Li by
pyrolysis to the powder above, and firing the mixture at 1,500 to
1,800.degree. C. in an inert gas atmosphere under 0.08 to 0.1 MPa.
As for the firing atmosphere, the firing is preferably performed in
a nitrogen atmosphere under atmospheric pressure. In particular, by
performing the synthesis in a nitrogen-containing inert gas
atmosphere under atmospheric pressure, the production cost of the
Li-containing .alpha.-sialon-based phosphor can be reduced.
[0114] The production process of the Li-containing
.alpha.-sialon-based phosphor powder can be fundamentally the same
as that described above except for using an amorphous silicon
nitride powder and/or a nitrogen-containing silane compound and
adding an excess of Li oxide or precursor substance capable of
becoming an oxide of Li by pyrolysis in addition to the raw
materials of the Li-containing .alpha.-sialon represented by
formula (1).
[0115] An oxide of Li or a precursor substance capable of becoming
an oxide of Li is added in excess, and examples of the precursor
substance capable of becoming an oxide of Li by pyrolysis include
respective metal salts such as carbonate, oxalate, citrate, basic
carbonate and hydroxide.
[0116] The mixture of starting materials is fired at 1,500 to
1,800.degree. C., preferably at 1,550 to 1,700.degree. C., in a
nitrogen-containing inert gas atmosphere under atmosphere pressure
or reduced pressure to obtain the objective Li-containing
.alpha.-sialon phosphor powder. Examples of the inert gas include
helium, argon, neon and krypton, but such a gas may also be used by
mixing it with a small amount of hydrogen gas. If the firing
temperature is less than 1,500.degree. C., an impracticably long
period of heating is required for the production of the desired
Li-containing .alpha.-sialon-based phosphor powder, and the
proportion of Li-containing .alpha.-sialon-based phosphor phase in
the powder produced is also reduced. If the firing temperature
exceeds 1,800.degree. C., there arises an undesirable problem that
silicon nitride and sialon are sublimated and decomposed to produce
free silicon. The firing time is preferably from 1 to 48 hours. In
particular, a firing time of 1 to 24 hours at a firing temperature
of 1,600 to 1,700.degree. C. is most preferred, because a phosphor
particle excellent in the particle shape and composition can be
obtained.
[0117] The Li-containing .alpha.-sialon-based phosphor powder
activated by a rare earth element emits fluorescence having a peak
wavelength of 560 to 580 nm when excitation light is injected. The
preferred rare earth element-activated Li-containing
.alpha.-sialon-based phosphor powder is caused to emit fluorescence
having a main wavelength of 570 to 574 nm by injecting excitation
light.
[0118] Also, any of the rare earth element-activated Li-containing
.alpha.-sialon-based phosphors is kneaded with a transparent resin
such as epoxy resin and acrylic resin by a known method to produce
a coating agent, and a light-emitting diode whose surface is coated
with the coating agent can be used as a light-emitting device for
various lighting devices.
[0119] In particular, a light emitting source in which the peak
wavelength of excitation light is from 330 to 500 nm is suitable
for the Li-containing .alpha.-sialon-based phosphor. In the
ultraviolet region, the luminous efficiency of the Li-containing
.alpha.-sialon-based phosphor is high and a light-emitting device
having good performance can be fabricated. A high luminous
efficiency is also obtained using a blue light source and by
combining yellow fluorescence of the Li-containing
.alpha.-sialon-based phosphor and blue excitation light, a
light-emitting device giving good daytime white color or daylight
color can be fabricated.
[0120] Furthermore, by combining a red phosphor of 600 to 650 nm
for the adjustment of color tone, the emission color of daytime
white color or daylight color can be controlled to fall in the warm
bulb color region. The light-emitting device of such bulb color can
be widely used for general domestic lighting.
[0121] Also, any of the rare earth element-activated Li-containing
.alpha.-sialon-based phosphors can be applied to fabricate an image
display device by using the Li-containing .alpha.-sialon-based
phosphor. In this case, the above-described light-emitting device
may be used but the Li-containing .alpha.-sialon-based phosphor can
also be directly excited to emit light by using an excitation light
such as electron beam, electric field and ultraviolet ray, for
example, can be used on the principle like that of a fluorescent
lamp. Even with such a light-emitting device, an image display
device can be fabricated.
EXAMPLES
[0122] Our phosphors, devices and methods are described in greater
detail below by referring to specific examples.
Examples 1 to 8
[0123] A lithium carbonate powder, a lithium nitride powder, a
europium oxide powder, an aluminum nitride powder and an amorphous
silicon nitride powder obtained by reacting silicon tetrachloride
and ammonia, or crystalline silicon nitride having a specific
surface area of about 9.2 m.sup.2/g were weighed to give the
composition in Table 1. In Table 1, the raw material composition is
expressed in mol %, and in Table 2, the raw material composition is
expressed in wt %. A nylon ball for stirring and the weighed
powders were put in a vessel and mixed by a vibration mill for 1
hour in a nitrogen atmosphere. After the mixing, the resulting
powder was taken out and filled in a boron nitride-made crucible.
At this time, the filing density was about 0.5 g/cm.sup.3 when
using crystalline silicon nitride and about 0.18 g/cm.sup.3 when
using amorphous silicon nitride. The crucible was set in a
resistance heating furnace and heated in a nitrogen gas flow
atmosphere under atmospheric pressure according to a
temperature-rising schedule of holding the temperature at from room
temperature to 1,000.degree. C. for 1 hour and at from 1,000 to
1,250.degree. C. for 2 hours and raising the temperature from
1,250.degree. C. to the objective temperature shown in Table 3 at
200.degree. C/h, whereby a phosphor powder was obtained. This
powder was obtained as a lump due to weak sintering and, therefore,
lightly ground in an agate mortar until obtaining a powder free
from a large lump and after performing an acid treatment by dipping
and stirring the powder in a 2 N nitric acid solution for 5 hours,
the resulting powder was dried at a temperature of 110.degree. C.
for 5 hours to obtain a powder.
[0124] The X-ray diffraction pattern of the powder obtained was
measured, and identification of the crystal phase was performed. As
a result, in all Examples, the powder was confirmed to be
substantially a Li-containing .alpha.-sialon-based phosphor.
Subsequently, the compositional analysis of the powder obtained was
performed. Oxygen and nitrogen contained in the Li-containing
.alpha.-sialon-based phosphor were analyzed in an oxygen-nitrogen
simultaneous analyzer manufactured by LECO. As for Li, the sample
was acidolyzed with nitric acid and hydrofluoric acid under
pressure, sulfuric acid was added thereto, the resulting mixture
was concentrated by heating until a white fume was generated,
hydrochloric acid was added thereto and after dissolving under
heating, the resulting solution was quantitatively analyzed by the
ICP-AES method using Model SPS5100 manufactured by SII
Nanotechnology. As for Si, the sample was melted by overheating
with sodium carbonate and boric acid and then dissolved with
hydrochloric acid, and the obtained solution was quantitatively
analyzed in accordance with the coagulation gravimetric method. As
for Li and Eu, the filtrate obtained in the pretreatment of the
quantitative analysis of Si was collected and quantitatively
analyzed by ICP-AES. The results are shown in Table 3. These
powders were further evaluated for the peak wavelength and peak
intensity of the fluorescence by using FP-6500 with an integrating
sphere manufactured by JASCO Corporation. Incidentally, the
excitation wavelength of the fluorescence spectrum was set to 450
nm. The results are shown in Table 4. 2 was used as the valence a
of Eu when calculating .delta..
[0125] With respect to Example 2 using amorphous silicon nitride as
a raw material and Example 6 using crystalline silicon nitride, the
particle morphology was observed by scanning electron microscopes
(SEM) 54800 manufactured by Hitachi High-Technologies Corporation
and JSM-7000F manufactured by JEOL Ltd. The observation was
performed for the particle morphology after acid treatment (FIGS.
1A and 1B) and then, performed for the classified product obtained
by removing extremely large particles and extremely small particles
from the powder so that the powder can be used as a phosphor (FIGS.
2A, 2B, 3A and 3B). Specifically, the powder was passed through a
sieve of 20 .mu.m and fine particles were removed by the
powder-to-water ratio.
[0126] Based on SEM photographs, the area of particles in each
photograph was determined using an image analysis software Image J,
the equivalent-circle particle diameter was determined from the
area, and the average particle diameter was determined. The results
are shown in Table 4. Also, about 20 visually average primary
particles were extracted and the average of their particle
diameters was determined, as a result, the obtained value
substantially agreed with the average equivalent-circle diameter.
The average particle diameter of the Li-containing .alpha.-sialon
using amorphous silicon nitride was from 1 to 3 .mu.m. The aspect
ratio was 2 or less in all Examples. In the powder using amorphous
silicon nitride for the raw material, a primary powder could be
clearly distinguished, but in the powder using crystalline silicon
nitride, a secondary particle where primary particles are densely
fused/aggregated was formed, and the image analysis was difficult.
Therefore, about 20 visually average primary particles were
extracted, and the average of their particle diameters was
determined. The results are shown in Table 4. The primary particle
diameter was about 0.5 .mu.m and by far smaller than that when
using amorphous silicon nitride.
[0127] Also, with respect to particles in the analysis region, the
existence ratio of particles of 0.8 .mu.m or more was determined.
The area of all particles in the measurement region and the area of
particles of 0.8 .mu.m or more were determined, and the ratio
therebetween was calculated. The results are shown in Table 4. In
all samples, the area ratio was 70% or more.
[0128] The classified product of Example 2 was measured for the
particle size distribution by using a laser diffraction/scattering
particle size distribution measuring apparatus, LA-910,
manufactured by Horiba Ltd. The measuring method was as follows. A
dispersion medium containing 0.03 wt % of SN Dispersant produced by
San Nopco Limited was put into a flow cell, and a blank measurement
was performed. Subsequently, the sample was added to a dispersion
medium having the same composition and ultrasonically dispersed for
60 minutes. The measurement was performed by adjusting the amount
of the sample so that the transmittance of the solution became from
70 to 95%. The measurement results were corrected by the previously
measured blank measurement results to determine the particle size
distribution. FIGS. 2A and 3A show the SEM photograph of this
powder. FIG. 4A shows the results of the particle size distribution
measurement. The frequency distribution curve exhibited a good
one-peak curve. D10, D50 and D90 are shown in Table 4. The specific
surface area of this powder was measured by FlowSorb Model 2300
manufactured by Shimadzu Corporation and found to be 1.52
m.sup.2/g. The classified product of Example 4 was also measured
for D10, D50 and D90 and exhibited a good one-peak curve as the
frequency distribution curve.
[0129] Furthermore, the particle size distribution measurement was
performed with respect to Example 6. FIGS. 2B and 3B show the SEM
photograph of this powder. FIG. 4B shows the measurement results of
the particle size distribution. The frequency distribution curve
exhibited a two-peak curve. D10, D50 and D90 are shown in Table 4.
The specific surface area of this powder was measured by FlowSorb
Model 2300 manufactured by Shimadzu Corporation and found to be
2.50 m.sup.2/g. The classified product of Example 7 was also
measured for D10, D50 and D90 and exhibited a two-peak curve as the
frequency distribution curve. D90 of Example 7 exceeded 20 .mu.m
and this is considered to result because fine particles and large
particles were aggregated during measurement.
[0130] When a Li-containing .alpha.-sialon-based phosphor powder
was produced using crystalline silicon nitride, a powder composed
of a secondary particle resulting from fusion/aggregation of small
primary particles is obtained, and when this powder is pulverized
to provide a phosphor, fine particles as the secondary particle
debris and large secondary particles are allowed to exist. With
such powder, scattering is increased due to fine particles,
decreasing the fluorescence intensity, and the particle size
distribution is greatly reduced.
Comparative Example 1
[0131] A phosphor powder was produced according to the formulation
shown in Table 1 by the same method as in Example 1. Furthermore,
the identification and compositional analysis of the crystal phase
were performed by the same method as in Example 1. As a result of
analysis of the crystal phase, the powder obtained was a powder
composed of a Li-containing .alpha.-sialon-based phosphor single
phase. The analyzed composition is shown in Table 3. The x value of
the Li-containing .alpha.-sialon-based phosphor was 0.39. The
fluorescence intensity of this Li-containing .alpha.-sialon-based
phosphor powder was low. These results reveal that when the x-value
is less than 0.45, good fluorescence intensity cannot be
obtained.
Comparative Example 2
[0132] A phosphor powder was produced according to the formulation
shown in Table 1 by the same method as in Example 1. Furthermore,
the identification and compositional analysis of the crystal phase
were performed by the same method as in Example 1. As a result of
analysis of the crystal phase, the powder obtained was a powder
composed of a Li-containing .alpha.-sialon-based phosphor and
slight heterophase. The analyzed composition is shown in Table 3.
Incidentally, the powder contained the heterophase in a very small
proportion and was composed mostly of a Li-containing
.alpha.-sialon phosphor and therefore, the calculation was
performed in disregard of the heterophase. The x value and .delta.
of the Li-containing .alpha.-sialon-based phosphor were 0.9 and
-0.2, respectively. The fluorescence intensity of this
Li-containing .alpha.-sialon-based phosphor powder was low. These
results reveal that when .delta. is less than 0, good fluorescence
intensity cannot be obtained.
Comparative Example 3
[0133] A phosphor powder was produced according to the formulation
shown in Table 1 by the same method as in Example 1 except for
using crystalline silicon nitride having a specific surface area of
about 9.2 m.sup.2/g as the silicon nitride raw material and
subjected to acid washing in the same manner. Furthermore, the
identification and compositional analysis of the crystal phase were
performed by the same method as in Example 1. As a result of
analysis of the crystal phase, the powder obtained was a powder
composed of a Li-containing .alpha.-sialon-based phosphor and
slight heterophase. The analyzed composition is shown in Table 3.
Incidentally, the powder contained the heterophase in a very small
proportion and was composed mostly of a Li-containing
.alpha.-sialon phosphor and, therefore, the calculation was
performed in disregard of the heterophase. The x value and .delta.
of the Li-containing .alpha.-sialon-based phosphor were 0.82 and
0.0, respectively. The fluorescence intensity ratio stood at the
small value of 68.
Example 9
[0134] The phosphor of Example 2 and epoxy resin were mixed in a
weight ratio of 20:100 to produce a phosphor paste. This paste was
coated on a blue light-emitting diode (wavelength: 470 nm) fixed to
an electrode and heated at 120.degree. C. for 1 hour and further at
150.degree. C. for 12 hours to cure the epoxy resin. The obtained
light-emitting diode was lit, and the light was confirmed to be
white light of daylight color.
Example 10
[0135] The phosphor of Example 2 and a separately prepared red
phosphor CaAlSiN.sub.3 were mixed to adjust the color tone of the
phosphor. The results are shown in Table 5. White LEDs ranging from
daylight color to bulb color could be produced by combining a blue
LED according to the change in the color tone shown in Table 5.
TABLE-US-00001 TABLE 1 Li.sub.2CO.sub.3 Li.sub.3N Eu.sub.2O.sub.3
AlN Si.sub.3N.sub.4 (mol %) (mol %) (mol %) (mol %) (mol %) Example
1 13.41 0.89 0.54 46.18 38.98 Example 2 13.41 0.89 0.54 46.18 38.98
Example 3 15.09 1.26 0.48 51.09 32.08 Example 4 15.80 1.45 0.46
53.21 29.08 Example 5 13.41 0.89 0.54 46.18 38.98 Example 6 13.41
0.89 0.54 46.18 38.98 Example 7 13.41 0.89 0.54 46.18 38.98 Example
8 9.75 0.39 0.65 35.49 53.73 Comparative Example 1 9.75 0.39 0.65
35.49 53.73 Comparative Example 2 0.59 12.88 0.78 22.73 63.03
Comparative Example 3 0.63 11.50 0.84 17.02 70.00
TABLE-US-00002 TABLE 2 Li.sub.2CO.sub.3 Li.sub.3N Eu.sub.2O.sub.3
AlN Si.sub.3N.sub.4 (wt %) (wt %) (wt %) (wt %) (wt %) Example 1
11.56 0.36 2.20 22.09 63.79 Example 2 11.56 0.36 2.20 22.09 63.79
Example 3 14.08 0.55 2.15 26.43 56.79 Example 4 15.28 0.66 2.12
28.55 53.39 Example 5 11.56 0.36 2.20 22.09 63.79 Example 6 11.56
0.36 2.20 22.09 63.79 Example 7 11.56 0.36 2.20 22.09 63.79 Example
8 7.24 0.14 2.30 14.61 75.72 Comparative Example 1 7.24 0.14 2.30
14.61 75.72 Comparative Example 2 0.41 4.26 2.60 8.84 83.89
Comparative Example 3 0.41 3.56 2.63 6.20 87.21
TABLE-US-00003 TABLE 3 Silicon Nitride Firing Temperature Firing
Time Species (.degree. C.) (h) x y m n x/m n + .delta. .delta.
Example 1 amorphous 1700 1 0.82 0.02 1.58 1.50 0.52 2.22 0.72
Example 2 amorphous 1650 3 0.98 0.01 1.14 2.14 0.86 2.28 0.14
Example 3 amorphous 1650 3 1.13 0.05 1.57 2.27 0.72 2.61 0.34
Example 4 amorphous 1700 3 1.08 0.02 1.76 2.16 0.61 2.80 0.64
Example 5 crystalline 1700 3 0.71 0.08 2.05 0.56 0.35 1.74 1.18
Example 6 crystalline 1650 3 0.84 0.04 0.96 1.50 0.88 1.54 0.04
Example 7 crystalline 1600 3 0.97 0.03 1.09 2.04 0.89 2.10 0.06
Example 8 amorphous 1700 3 0.45 0.05 1.08 0.79 0.42 1.32 0.53
Comparative crystalline 1700 3 0.39 0.10 1.12 0.29 0.35 0.82 0.53
Example 1 Comparative crystalline 1700 3 0.90 0.10 0.90 0.65 1.00
0.45 -0.20 Example 2 Comparative crystalline 1650 3 0.82 0.05 0.92
0.30 0.89 0.30 0.00 Example 3
TABLE-US-00004 TABLE 4 Average Particle Average Existence
Fluorescence Peak Diameter Aspect Area D10 D50 D90 Wavelength
Fluorescence Intensity (.mu.m) Ratio (%) (.mu.m) (.mu.m) (.mu.m)
(nm) Ratio (%) Example 1 1.3 1.3 78.5 -- -- -- 578.0 238 Example 2
1.4 1.4 70.4 2.6 4.9 9.3 571.0 298 Example 3 2.2 1.4 95.0 -- -- --
572.5 321 Example 4 2.8 1.3 95.6 3.2 7.2 14.8 570.0 251 Example 5
0.46 -- -- -- -- -- 580.0 100 Example 6 0.6 -- -- 0.89 3.7 17.2
578.5 120 Example 7 0.51 -- -- 1.2 15.8 25.5 573.0 196 Example 8
1.6 1.3 97.2 -- -- -- 574.5 161 Comparative 0.45 -- -- -- -- --
574.5 98 Example 1 Comparative 0.4 -- -- -- -- -- 586.5 38 Example
2 Comparative 0.4 -- -- -- -- -- 580.0 68 Example 3
TABLE-US-00005 TABLE 5 Mixing Ratio of Phosphor Powders (wt %)
Li-Containing .alpha.- Red Color Tone Sialon-Based Phosphor
Phosphor x y Example 10-1 100 0 0.4489 0.5273 Example 10-2 99 1
0.4687 0.5070 Example 10-3 97 3 0.4946 0.4825 Example 10-4 95 5
0.5508 0.4315
Example 11
[0136] A lithium carbonate powder, a europium oxide powder, an
aluminum nitride powder, an aluminum oxide powder and an amorphous
silicon nitride powder obtained by reacting silicon tetrachloride
and ammonia were weighed to give x=0.85, y=0.2, m=1.25 and n=1.0,
and furthermore, as an excess additive, lithium carbonate was added
in an amount of, in terms of metal Li, 0.63 mol per mol of
Li-containing .alpha.-sialon. A nylon ball for stirring and the
weighed powders were put in a vessel and mixed by a vibration mill
for 1 hour in a nitrogen atmosphere. After the mixing, the
resulting powder was taken out and filled in a boron nitride-made
crucible. At this time, the filing density was about 0.18
g/cm.sup.3. The crucible was set in a heat resistant furnace and
heated by holding the temperature at from room temperature to
1,000.degree. C. for 1 hour and at from 1,000 to 1,250.degree. C.
for 2 hours and raising the temperature from 1,250.degree. C. to
1,600.degree. C. at 200.degree. C./h. The holding time was set to 3
hours, and a phosphor powder was obtained. This powder was obtained
as a lump due to weak sintering and, therefore, the powder was
lightly ground in an agate mortar until obtaining a powder free
from a large lump and then subjected to an acid treatment by
dipping and stirring the powder in a 2 N nitric acid solution for 5
hours. The resulting powder was dried at a temperature of
110.degree. C. for 5 hours.
[0137] The powder obtained was analyzed for the composition by the
same method as in Example 1, as a result, x=0.64, y=0.10, m=0.91,
n=2.12, x/m=0.70 and .delta.=0.07.
[0138] Furthermore, the particle morphology of the powder obtained
was observed using a scanning electron microscope (SEM), JSM-7000F,
manufactured by JEOL Ltd. FIG. 5 shows the results. As shown in
FIG. 5, a Li-containing .alpha.-sialon-based phosphor powder
containing a Li-containing .alpha.-sialon phosphor particle which
is a primary particle such that the average aspect ratio of
particles of 3 .mu.m or more is 1.3 and the length of short axis is
3.3 .mu.m, i.e., the length of the short axis is larger than 3
.mu.m, could be obtained.
[0139] The X-ray diffraction pattern of this powder was measured to
identify the crystal phase. Incidentally, K.alpha. of Cu was used
as the X-ray source. As a result, the principal peak was confirmed
to be Li-containing .alpha.-sialon. An X-ray was precisely scanned
to determined the lattice constant and the results were hexagonal,
a=7.812 .ANG. and c=5,666 .ANG..
[0140] Fluorescence characteristics are described below. Envisaging
use of the phosphor in practice, a classified product obtained by
removing extremely large particles and extremely small particles
was employed as the sample. More specifically, large particle lumps
were removed by passing the powder through a sieve of 20 .mu.m, and
extremely fine particles were further removed at the
powder-to-water ratio.
[0141] The fluorescence characteristics were measured using FP-6500
with an integrating sphere manufactured by JASCO Corporation. The
result was 270% with the same scale as in Table 4.
Example 12
[0142] Raw materials were weighed and mixed to give the same
composition as in Example 2 except for using, as the raw material,
silicon diimide in place of amorphous silicon nitride powder. The
mixed powder was filled in a silicon nitride crucible. At this
time, the filing density was 0.09 g/cm.sup.3. The crucible was set
in a resistance heating furnace and heated in a nitrogen gas flow
atmosphere under atmospheric pressure according to a
temperature-rising schedule of holding the temperature at from room
temperature to 800.degree. C. for 1 hour, at from 800 to
1,000.degree. C. for 2 hours and at from 1,000 to 1,250.degree. C.
for 2 hours and raising the temperature from 1,250.degree. C. to
1,650.degree. C. at 200.degree. C./h, whereby a phosphor powder was
obtained. The powder obtained was treated by the same method as in
Example 2 and subjected to analysis of the composition. The results
were x=0.90, y=0.03, m=1.13, n=2.23, x/m=0.80 and 6=0.17. The
fluorescence wavelength was 572 nm, and the fluorescence intensity
was 293% when expressed by the intensity ratio of Table 4.
* * * * *