U.S. patent application number 15/347038 was filed with the patent office on 2018-03-15 for method of producing nitride fluorescent material, nitride fluorescent material, and light-emitting device using the same.
This patent application is currently assigned to NICHIA CORPORATION. The applicant listed for this patent is NICHIA CORPORATION. Invention is credited to Shoji HOSOKAWA, Sadakazu WAKUI.
Application Number | 20180072948 15/347038 |
Document ID | / |
Family ID | 58663286 |
Filed Date | 2018-03-15 |
United States Patent
Application |
20180072948 |
Kind Code |
A9 |
WAKUI; Sadakazu ; et
al. |
March 15, 2018 |
METHOD OF PRODUCING NITRIDE FLUORESCENT MATERIAL, NITRIDE
FLUORESCENT MATERIAL, AND LIGHT-EMITTING DEVICE USING THE SAME
Abstract
A method of producing a nitride fluorescent material having a
high light emission intensity and including a calcined product
having a composition represented by formula
M.sup.a.sub.vM.sup.b.sub.wM.sup.c.sub.xM.sup.d.sub.yN.sub.z is
provided. M.sup.a is at least one element selected from Sr, Ca, Ba,
and Mg; M.sup.b is at least one element selected from Li, Na, and
K; M.sup.c is at least one element selected from Eu, Mn, Tb, and
Ce; M.sup.d is at least one element selected from Al, B, Ga, and
In; v, w, x, y, and z satisfy 0.8.ltoreq.v.ltoreq.1.1,
0.8.ltoreq.w.ltoreq.1.1, 0.001<x.ltoreq.0.1,
2.0.ltoreq.y.ltoreq.4.0, and 3.0.ltoreq.z.ltoreq.5.0, respectively.
The nitride fluorescent material includes elemental oxygen in a
range of 2% or more and 4% or less by mass. The method includes
mixing the calcined product with a polar solvent having a relative
dielectric constant in a range of 10 or more and 70 or less at
20.degree. C.
Inventors: |
WAKUI; Sadakazu; (Tokushima
-shi, JP) ; HOSOKAWA; Shoji; (Tokushima -shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NICHIA CORPORATION |
Anan-shi |
|
JP |
|
|
Assignee: |
NICHIA CORPORATION
Anan-shi
JP
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20170130126 A1 |
May 11, 2017 |
|
|
Family ID: |
58663286 |
Appl. No.: |
15/347038 |
Filed: |
November 9, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09K 11/7734 20130101;
H01L 33/62 20130101; H01L 33/504 20130101; H01L 33/486 20130101;
H01L 2933/0041 20130101; H01L 33/32 20130101; H01L 33/50 20130101;
H01L 2924/181 20130101; H01L 2224/32245 20130101; H01L 2224/73265
20130101; H01L 33/56 20130101; H01L 2224/48091 20130101; C09K
11/0883 20130101; H01L 2224/48247 20130101; H01L 2224/48257
20130101; H01L 2224/48091 20130101; H01L 2924/00014 20130101; H01L
2924/181 20130101; H01L 2924/00012 20130101; H01L 2224/73265
20130101; H01L 2224/32245 20130101; H01L 2224/48247 20130101; H01L
2924/00 20130101; H01L 2224/73265 20130101; H01L 2224/32245
20130101; H01L 2224/48257 20130101; H01L 2924/00 20130101; H01L
2224/73265 20130101; H01L 2224/32245 20130101; H01L 2224/48247
20130101; H01L 2924/00012 20130101 |
International
Class: |
C09K 11/77 20060101
C09K011/77; C09K 11/08 20060101 C09K011/08; H01L 33/50 20060101
H01L033/50; H01L 33/32 20060101 H01L033/32; H01L 33/56 20060101
H01L033/56; H01L 33/48 20060101 H01L033/48; H01L 33/62 20060101
H01L033/62 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 11, 2015 |
JP |
2015-221127 |
Nov 8, 2016 |
JP |
2016-217905 |
Claims
1. A method of producing a nitride fluorescent material, the
nitride fluorescent material comprising a calcined product having a
composition represented by a formula (I):
M.sup.a.sub.vM.sup.b.sub.wM.sup.c.sub.xM.sup.d.sub.yN.sub.z (I)
wherein M.sup.a is at least one element selected from the group
consisting of Sr, Ca, Ba, and Mg; M.sup.b is at least one element
selected from the group consisting of Li, Na, and K; M.sup.c is at
least one element selected from the group consisting of Eu, Mn, Tb,
and Ce; M.sup.d is at least one element selected from the group
consisting of Al, B, Ga, and In; v, w, x, y, and z are numbers
satisfying 0.8.ltoreq.v.ltoreq.1.1, 0.8.ltoreq.w.ltoreq.1.1,
0.001<x.ltoreq.0.1, 2.0.ltoreq.y.ltoreq.4.0, and
3.0.ltoreq.z.ltoreq.5.0, respectively, and having a content of
elemental oxygen in a range of 2% by mass or more and 4% by mass or
less, the method comprising: providing a calcined product having
the composition represented by the formula (I); and mixing the
calcined product with a polar solvent having a relative dielectric
constant in a range of 10 to 70 at 20.degree. C.
2. The method of producing a nitride fluorescent material according
to claim 1, wherein the polar solvent further comprises water, and
a content of water in the polar solvent is in a range of 0.01% by
mass or more and 12% by mass or less.
3. The method of producing a nitride fluorescent material according
to claim 2, wherein the content of water in the polar solvent is in
a range of 0.1% by mass or more and 10% by mass or less.
4. The method of producing a nitride fluorescent material according
to claim 1, wherein the polar solvent has a relative dielectric
constant in a range of 10 or more and 35 or less at 20.degree.
C.
5. The method of producing a nitride fluorescent material according
to claim 1, wherein the polar solvent is alcohol and/or ketone.
6. The method of producing a nitride fluorescent material according
to claim 1, wherein the polar solvent is at least one selected from
the group consisting of methanol, ethanol, 1-propanol, 2-propanol,
and acetone.
7. The method of producing a nitride fluorescent material according
to claim 1, comprising, after the steps, a step of classifying the
calcined product to yield a nitride fluorescent material having an
average particle size of 4.0 .mu.m or more.
8. The method of producing a nitride fluorescent material according
to claim 1, wherein in the formula (I), M.sup.a comprises at least
one of Sr and Ca, M.sup.b comprises Li, M.sup.c is Eu, and M.sup.d
is Al.
9. A method of producing a nitride fluorescent material, the method
comprising the steps of: preparing a calcined product having a
composition represented by following formula (I):
M.sup.a.sub.vM.sup.b.sub.wM.sup.c.sub.xM.sup.d.sub.yN.sub.z (I)
wherein M.sup.a is at least one element selected from the group
consisting of Sr, Ca, Ba, and Mg; M.sup.b is at least one element
selected from the group consisting of Li, Na, and K; M.sup.c is at
least one element selected from the group consisting of Eu, Mn, Tb,
and Ce; M.sup.d is at least one element selected from the group
consisting of Al, B, Ga, and In; and v, w, x, y, and z are numbers
satisfying 0.8.ltoreq.v.ltoreq.1.1, 0.8.ltoreq.w.ltoreq.1.1,
0.001<x.ltoreq.0.1, 2.0.ltoreq.y.ltoreq.4.0, and
3.0.ltoreq.z.ltoreq.5.0, respectively; and mixing the calcined
product with a polar solvent, wherein the polar solvent is alcohol
and/or ketone containing water in a range of 0.01% by mass or more
and 12% by mass or less.
10. The method of producing a nitride fluorescent material
according to claim 9, wherein the content of water in the polar
solvent is in a range of 0.1% by mass or more and 10% by mass or
less.
11. The method of producing a nitride fluorescent material
according to claim 9, wherein in the formula (I), Ma comprises at
least one of Sr and Ca, Mb comprises Li, Mc is Eu, and Md is
Al.
12. A nitride fluorescent material comprising a calcined product
having a composition represented by following formula (I):
M.sup.a.sub.vM.sup.b.sub.wM.sup.c.sub.xM.sup.d.sub.yN.sub.z (I)
wherein M.sup.a is at least one element selected from the group
consisting of Sr, Ca, Ba, and Mg; M.sup.b is at least one element
selected from the group consisting of Li, Na, and K; M.sup.c is at
least one element selected from the group consisting of Eu, Mn, Tb,
and Ce; M.sup.d is at least one element selected from the group
consisting of Al, B, Ga, and In; and v, w, x, y, and z are numbers
satisfying 0.8.ltoreq.v.ltoreq.1.1, 0.8.ltoreq.w.ltoreq.1.1,
0.001<x.ltoreq.0.1, 2.0.ltoreq.y.ltoreq.4.0, and
3.0.ltoreq.z.ltoreq.5.0, respectively, and having a content of
elemental oxygen in a range of 2% by mass or more and 4% by mass or
less.
13. The nitride fluorescent material according to claim 12, wherein
a content of elemental fluorine is in a range of 0.1% by mass or
more and 1% by mass or less.
14. The nitride fluorescent material according to claim 12, wherein
an internal quantum efficiency is 80% or more.
15. The nitride fluorescent material according to claim 12, wherein
in the formula (I), M.sup.a comprises at least one of Sr and Ca,
M.sup.b comprises Li, M.sup.c is Eu, and M.sup.d is Al.
16. A light-emitting device comprising the nitride fluorescent
material according to claim 12 and an excitation light source.
17. The light-emitting device according to claim 16, comprising a
second fluorescent material having an peak fluorescence wavelength
different from that of the nitride fluorescent material, wherein
the second fluorescent material comprises at least one fluorescent
material having a composition selected from the group consisting of
compositions represented by following formulae:
Si.sub.6-pAl.sub.pO.sub.pN.sub.8-p:Eu (where 0<p.ltoreq.4.2)
(Ca,Sr).sub.8MgSi.sub.4O.sub.16(Cl,F,Br).sub.2:Eu
(Ba,Sr,Ca)Ga.sub.2S.sub.4:Eu (Ba,Sr)MgAl.sub.10O.sub.17:Mn
(Sr,Ca)AlSiN.sub.3:Eu, and K.sub.2(Si,Ge,Ti)F.sub.6:Mn.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of Japanese Patent
Application No. 2015-221127, filed on Nov. 11, 2015 and Japanese
Patent Application No. 2016-217905, filed on Nov. 8, 2016, the
entire disclosures of which are incorporated herein by
reference.
BACKGROUND
[0002] Technical Field
[0003] The present disclosure relates to a method of producing a
nitride fluorescent material, the nitride fluorescent material, and
a light-emitting device using the same.
[0004] Description of Related Art
[0005] Light-emitting devices including combinations of a light
emitting diode (hereinafter may be referred to as "LED") and a
fluorescent material have been increasingly applied as lighting
apparatuses and backlights for liquid crystal displays, etc. For
example, in the case where such light emitting devices are used in
a liquid crystal display, a fluorescent material of a narrow half
bandwidth is desired to provide a wider range of color
reproducibility.
[0006] Examples of such a phosphor include a red light-emitting
phosphor of SrLiAl.sub.3N.sub.4:Eu (hereinafter may be referred to
as "SLAN phosphor"). For example, Patent Literature (PTL) 1 and
Non-Patent Literature (NPL) 1 (Philipp Pust et al. "Narrow-band
red-emitting Sr[LiA.sub.3N.sub.4]:Eu.sup.2+ as a next-generation
LED-phosphor material" Nature Materials, NMAT4012, VOL 13 September
2014) disclose SLAN phosphors having a narrow half bandwidth of 70
nm or less and having a peak fluorescence wavelength near 650
nm.
[0007] As disclosed in NPL1, a SLAN phosphor is, for example,
produced such that powder of raw materials including lithium
aluminum hydride (LiAlH.sub.4), aluminum nitride (AlN), strontium
hydride (SrH.sub.2), and europium fluoride (EuF.sub.3) are weighed
in a stoichiometric ratio so that Eu is 0.4 mol % and mixed. The
mixture is placed in a crucible and calcined in a mixed gas
atmosphere of hydrogen and nitrogen under atmospheric pressure at a
temperature of 1000.degree. C. for two hours.
CITATION LIST
Patent Literature
[0008] PTL 1: Japanese Laid-open Patent Publication No.
2015-526532
Non Patent Literature
[0008] [0009] NPL 1: Philipp Pust et al. "Narrow-band red-emitting
Sr[LiAl.sub.3N.sub.4]:Eu.sup.2+ as a next-generation LED-phosphor
material" Nature Materials, NMAT4012, VOL 13 September 2014
SUMMARY
[0010] The SLAN phosphors disclosed in PTL 1 and NPL 1 still have
room for further improvement in the light emission intensity. An
object of the present disclosure is to provide a method of
producing a nitride fluorescent material having a high light
emission intensity, a nitride fluorescent material, and a
light-emitting device using the same.
[0011] Specific examples for achieving the objects will be
described below. Certain embodiments of the present invention
include configurations illustrated below.
[0012] In a first embodiment, a method of producing a nitride
fluorescent material is provided. The nitride fluorescent material
includes a calcined product having a composition represented by a
formula (I):
M.sup.a.sub.vM.sup.b.sub.wM.sup.c.sub.xM.sup.d.sub.yN.sub.z (1)
in which, M.sup.a is at least one element selected from the group
consisting of Sr, Ca, Ba, and Mg; M.sup.b is at least one element
selected from the group consisting of Li, Na, and K; M.sup.c is at
least one element selected from the group consisting of Eu, Mn, Tb,
and Ce; M.sup.d is at least one element selected from the group
consisting of Al, B, Ga, and In; and v, w, x, y, and z are numbers
satisfying 0.8.ltoreq.v.ltoreq.1.1, 0.8.ltoreq.w.ltoreq.1.1,
0.001<x.ltoreq.0.1, 2.0.ltoreq.y.ltoreq.4.0, and
3.0.ltoreq.z.ltoreq.5.0, respectively, and includes elemental
oxygen at a content range of 2% by mass or more and 4% by mass or
less. The method includes preparing the calcined product having the
composition represented by formula (I), and mixing the calcined
product with a polar solvent having a relative dielectric constant
in a range of 10 or more and 70 or less at 20.degree. C.
[0013] In a second embodiment, a method of producing a nitride
fluorescent material is provided. The method includes preparing a
calcined product having a composition represented by a formula (I),
and mixing the calcined product with a polar solvent, in which the
polar solvent is alcohol and/or ketone and contains water in a
range of 0.01% by mass or more and 12% by mass or less,
wherein:
M.sup.a.sub.vM.sup.b.sub.wM.sup.c.sub.xM.sup.d.sub.yN.sub.z (I)
in which M.sup.a is at least one element selected from the group
consisting of Sr, Ca, Ba, and Mg; M.sup.b is at least one element
selected from the group consisting of Li, Na, and K; M.sup.c is at
least one element selected from the group consisting of Eu, Mn, Tb,
and Ce; M.sup.d is at least one element selected from the group
consisting of Al, B, Ga, and In; and v, w, x, y, and z are numbers
satisfying 0.8.ltoreq.v.ltoreq.1.1, 0.8.ltoreq.w.ltoreq.1.1,
0.001<x.ltoreq.0.1, 2.0.ltoreq.y.ltoreq.4.0, and
3.0.ltoreq.z.ltoreq.5.0, respectively.
[0014] In a third embodiment, a nitride fluorescent material
includes a calcined product having a composition represented by a
formula (I):
M.sup.a.sub.vM.sup.b.sub.wM.sup.c.sub.xM.sup.d.sub.yN.sub.z (I)
in which M.sup.a is at least one element selected from the group
consisting of Sr, Ca, Ba, and Mg; M.sup.b is at least one element
selected from the group consisting of Li, Na, and K; M.sup.c is at
least one element selected from the group consisting of Eu, Mn, Tb,
and Ce; M.sup.d is at least one element selected from the group
consisting of Al, B, Ga, and In; and v, w, x, y, and z are numbers
satisfying 0.8.ltoreq.v.ltoreq.1.1, 0.8.ltoreq.w.ltoreq.1.1,
0.001<x.ltoreq.0.1, 2.0.ltoreq.y.ltoreq.4.0, and
3.0.ltoreq.z.ltoreq.5.0, respectively, and includes elemental
oxygen at a content range of 2% by mass or more 4% by mass or
less.
[0015] In a fourth embodiment, a light-emitting device including a
nitride fluorescent material and an excitation light source is
provided.
[0016] One embodiment according to the present invention can
provide a method of producing a nitride fluorescent material having
a high light emission intensity, the nitride fluorescent material,
and a light-emitting device using the same.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic cross-sectional view showing an
exemplary light-emitting device.
[0018] FIG. 2 shows X-ray diffraction patterns of the nitride
fluorescent materials according to Examples and Comparative
Examples, and X-ray diffraction patterns of
Sr.sub.3Al.sub.2(OH).sub.12, LiAl.sub.2(OH).sub.7.2H.sub.2O, and a
compound (SLAN) represented by SrLiAl.sub.3N.sub.4.
[0019] FIG. 3 shows light emission spectra of nitride fluorescent
materials according to Example 1 and Comparative Example 1, showing
a relative light emission intensity to a wavelength.
[0020] FIG. 4 is an SEM image of the nitride fluorescent material
according to Example 1.
[0021] FIG. 5 is an SEM image of the nitride fluorescent material
according to Example 4.
[0022] FIG. 6 is an SEM image of the nitride fluorescent material
according to Comparative Example 6.
DETAILED DESCRIPTION
[0023] A method of producing a nitride fluorescent material, the
nitride fluorescent material, and a light-emitting device using the
same, according to the present disclosure will be described in
conjunction with illustrated embodiments. The embodiments described
below are intended as illustrative of a method of producing a
nitride fluorescent material, the nitride fluorescent material, and
a light-emitting device using the same, to give a concrete form to
technical ideas of the present invention, and the scope of the
invention is not limited to those described below. In the
specification, the relation between the color names and the
chromaticity coordinates, the relation between the ranges of
wavelength of light and the color names of single color light, and
the like conform to JIS Z8110. Further, the content of each
component in the composition is represented by a total amount in
the composition, when a plural number of substances each containing
corresponding component are present in the composition, unless
specifically indicated.
Method of Producing Nitride Fluorescent Material
[0024] The method of producing a nitride fluorescent material
according to one embodiment of the present invention is a method of
producing a nitride fluorescent material that includes a calcined
product having a composition represented by a formula (I):
M.sup.a.sub.vM.sup.b.sub.wM.sup.c.sub.xM.sup.d.sub.yN.sub.z (I)
in which M.sup.a is at least one element selected from the group
consisting of Sr, Ca, Ba, and Mg; M.sup.b is at least one element
selected from the group consisting of Li, Na, and K; M.sup.c is at
least one element selected from the group consisting of Eu, Mn, Tb,
and Ce; M.sup.d is at least one element selected from the group
consisting of Al, Si, B, Ga, In, Ge, and Sn, particularly
preferably at least one element selected from the group consisting
of Al, B, Ga, and In; and v, w, x, y, and z are numbers satisfying
0.8.ltoreq.v.ltoreq.1.1, 0.8.ltoreq.w.ltoreq.1.1,
0.001<x.ltoreq.0.1, 2.0.ltoreq.y.ltoreq.4.0, and
3.0.ltoreq.z.ltoreq.5.0, respectively, and includes elemental
oxygen at a content range of 2% by mass or more and 4% by mass or
less. The method includes providing the calcined product having the
composition represented by the formula (I) and mixing the calcined
product with a polar solvent having a relative dielectric constant
in a range of 10 or more and 70 or less at 20.degree. C.
[0025] The method of producing a nitride fluorescent material
according to another embodiment of the present invention, a method
of producing a nitride fluorescent material is provided. The method
includes preparing a calcined product that includes a composition
represented by the formula (I), and mixing the calcined product
with a polar solvent, in which the polar solvent is alcohol and/or
ketone that includes water in a range of 0.01% by mass or more and
12% by mass or less.
[0026] In the method of producing a nitride fluorescent material of
the present embodiment, it is preferable that in the composition
represented by the formula (I), M.sup.a includes at least one of Sr
and Ca, M.sup.b includes Li, M.sup.c is Eu, and M.sup.d is Al.
[0027] The method of the present embodiment includes mixing in
which particles of calcined product obtained by a heat treatment
are mixed with a polar solvent.
[0028] The fluorescent material obtained according to the method of
the present embodiment includes a hydroxide and/or an oxide formed
at least on a portion of the surface or a portion near the surface
of the particles of the calcined product. It is assumed that the
hydroxide and/or the oxide is originating from water contained in
the polar solvent while dispersing the particles of the calcined
product when mixing the calcined product having the composition
shown in the formula (I) and the polar solvent. It is also assumed
that with those hydroxides and/or oxides, for example, the
refractive index of the fluorescent material particles is adjusted,
which facilitates extraction of light from the fluorescent
particles, and thus, the emission intensity of the fluorescent
material can be enhanced.
Providing Calcined Product
[0029] To obtain a calcined product, the production methods of the
present embodiment each comprise mixing raw materials to prepare a
raw material mixture and heat treating the raw material mixture to
prepare the calcined product having a composition represented by
the formula (I).
Raw Material Mixture
[0030] The raw material mixture used in the production methods of
the present embodiment can contain any materials as long as the
calcined product having a composition represented by the formula
(I) can be obtained. For example, the raw material mixture can
contain at least one raw material selected from the group
consisting of single elemental metals contained in the composition
represented by the formula (I) and metal compounds thereof.
Examples of such metal compounds include hydrides, nitrides,
fluorides, oxides, carbonates, and chlorides thereof. A preferred
raw material is at least one selected from the group consisting of
hydrides, nitrides, and fluorides of the metal compounds in view of
the enhancement of the light emitting properties of the resulting
fluorescent material. When a raw material mixture contains metal
compounds of an oxide, a carbonate, a chloride, and the like, a
total content thereof is preferably 5% by mass or less, more
preferably 1% by mass or less in the raw material mixture. Of those
metal compounds, a fluoride or chloride can also be added to the
raw material mixture as a source of cations of element to obtain a
target ratio of cations in the resulting compound. This fluoride or
chloride of the metal compound can also serve as a flux component
described below.
[0031] The raw material mixture preferably contains a metal
compound containing a metal element selected from the group
consisting of Sr, Ca, Ba, and Mg as M.sup.a; a metal compound
containing a metal element selected from the group consisting of
Li, Na, and K as M.sup.b; a metal compound containing a metal
element selected from the group consisting of Eu, Mn, Tb, and Ce as
M.sup.c; and a metal compound containing a metal element selected
from the group consisting of Al, Si, B, Ga, In, Ge, and Sn as
M.sup.d.
[0032] Specific examples of the metal compound containing a metal
element (M.sup.a element) selected from the group consisting of Sr,
Ca, Ba, and Mg (hereinafter may also be referred to as "first metal
compound") include SrN.sub.2, SrN, Sr.sub.3N.sub.2, SrH.sub.2,
SrF.sub.2, Ca.sub.3N.sub.2, CaH.sub.2, CaF.sub.2, Ba.sub.3N.sub.2,
BaH.sub.2, BaF.sub.2, Mg.sub.3N.sub.2, MgH.sub.2, and MgF.sub.2,
and at least one of those is preferably employed.
[0033] The first metal compound preferably contains at least one of
Sr and Ca. When the first metal compound contains Sr, a portion of
the Sr may be substituted with one or more of Ca, Mg, Ba, etc. When
the first metal compound contains Ca, a portion of the Ca may be
substituted with one or more of Sr, Mg, Ba, etc. Such arrangement
allows for adjusting the peak fluorescence wavelength of the
nitride fluorescent material.
[0034] For the first metal compound, simple metal compounds as
described above can be used, or compounds such as imide compounds
and amide compounds can also be used. These first metal compounds
can be used alone or in combination of two or more.
[0035] The metal compound containing a metal element (M.sup.b
element) selected from the group consisting of Li, Na, and K
(hereinafter may also be referred to as "second metal compound")
preferably contains at least Li, more preferably at least one of a
nitride and a hydride of Li. When the second metal compound
contains Li, a portion of the Li may be substituted with Na, K, or
the like, and may contain another metal element forming the nitride
fluorescent material. For the second metal compound containing Li,
at least one selected from the group consisting of Li.sub.3N,
LiN.sub.3, LiH, and LiAlH.sub.4 is preferably used.
[0036] The metal compound containing a metal element (M.sup.d
element) selected from the group consisting of Al, Si, B, Ga, In,
Ge, and Sn (hereinafter may also be referred to as "third metal
compound") may be a metal compound substantially containing only a
metal element selected from the group consisting of Al, Si, B, Ga,
In, Ge, and Sn as a metal element, or may be a metal compound
containing a metal element partially substituted with another metal
element. The third metal compound is preferably a metal compound
containing only Al. The third metal compound may be a metal
compound containing Al partially substituted with a metal element
selected from the group consisting of Group 13 elements Ga and In
and Period 4 elements V, Cr and Co, or may be a metal compound
containing Al and another metal element forming the nitride
fluorescent material, such as Li. Specific examples of the third
metal compound containing Al can include AlN, AlH.sub.3, AlF.sub.3,
and LiAlH.sub.4, and at least one of those is preferably employed.
These third metal compounds can be used alone or in combination of
two or more.
[0037] The metal compound containing a metal element (M.sup.c
element) selected from the group consisting of Eu, Mn, Tb, and Ce
(hereinafter, also referred to as "fourth metal compound") may be a
metal compound substantially containing only a metal element
selected from the group consisting of Eu, Mn, Tb, and Ce as a metal
element or may be a metal compound containing a metal element
partially substituted with another metal element. The fourth metal
compound is preferably a metal compound containing Eu, which is
contained as an activator. A portion of Eu may be substituted with
one or more of Sc, Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm,
Yb, Lu, etc. The one or more elements substituting for a portion of
Eu are thought to act, for example, as co-activator. With the use
of the co-activator, the light emitting properties of the nitride
fluorescent material can be adjusted. In use of a mixture
containing Eu as an essential component for the nitride fluorescent
material, the mixing ratio can be changed as desired. Europium
mainly has divalent and trivalent energy levels. In the nitride
fluorescent material of the present embodiment, at least Eu.sup.2+
is used as an activator.
[0038] Specific examples of the fourth metal compound containing Eu
include Eu.sub.2O.sub.3, EuN, and EuF.sub.3, and at least one of
those is preferably employed. The nitride fluorescent material
according to the present embodiment contains a divalent Eu as an
emission center, but the divalent Eu is easily oxidized, so that a
metal compound that contains trivalent Eu can be included in the
raw material mixture.
[0039] In addition to the single elemental metals and the metal
compound as described above, the raw material mixture may also
contain other metal elements as required. Such other metal elements
can be contained in the raw material mixture, generally as an
oxide, a hydroxide, or the like, but such other metal elements may
be incorporated in a nitride, an imide, an amide, other inorganic
salts, etc., and may be preliminarily contained in the raw material
mixture.
[0040] The raw material mixture may contain a flux. Inclusion of
the flux in the raw material mixture can further accelerate the
reaction among the raw materials, and more uniform progress of the
solid phase reaction can be achieved, so that, a fluorescent
material having a large particle size and high light emitting
properties can be obtained. This is assumed, for example, that in a
production method where the heat treatment is performed at a
temperature range of 1000.degree. C. or more and 1300.degree. C. or
less, and a halide or the like is employed as the flux, the
temperature is almost equal to the liquid phase transition
temperature of the halide. Examples of the halides employed for the
flux include chlorides and fluorides of rare earth metals, alkaline
earth metals, and alkali metals. The flux of a compound can be
added to the raw material mixture as a source of cations of element
to obtain a target ratio of cations in the resulting compound, and
a fluoride is particularly preferable
[0041] When the raw material mixture contains a flux, the flux
component may accelerate the reaction, but an excessive amount of
the flux component may reduce the workability in the steps of
producing a nitride fluorescent material or may reduce the light
emission intensity of the resulting nitride fluorescent material.
For this reason, the content of the flux in the raw material
mixture is in a range of, for example, preferably 10% by mass or
less, more preferably 5% by mass or less. The raw material mixture
can contain a fluoride such as SrF.sub.2 or EuF.sub.3. In the case
of using such a fluoride, the content of the elemental fluorine
contained in the resulting fluorescent material is preferably in a
range of 0.1% by mass to 1% by mass.
Heat Treating
[0042] The production method according to the present embodiment
includes heat treating the raw material mixture in a nitrogen
atmosphere to provide the calcined product having a composition
represented by the formula (I). The calcined product having the
composition represented by the formula (I) can be provided, for
example, by heat treating the raw material mixture in an atmosphere
containing a nitrogen gas at a temperature in a range of
1000.degree. C. to 1400.degree. C. and a pressure in a range of 0.2
MPa to 200 MPa. Heat treating the raw material mixture at a
predetermined temperature under such an atmosphere containing
nitrogen gas under pressure can efficiently produce particles of a
calcined product that has a desired composition and a high light
emission intensity. The particles of the calcined product can also
be used as fluorescent material particles.
[0043] The raw material mixture prepared so as to attain the
composition represented by the formula (I) is heat treated to yield
a calcined product. The heat treatment can be performed with a gas
pressurizing electric furnace, for example. The heat treatment can
be performed at a temperature in a range of 1000.degree. C. or more
and 1400.degree. C. or less. The heat treatment temperature is
preferably at a temperature in a range of 1000.degree. C. or more
and 1300.degree. C. or less, more preferably 1100.degree. C. or
more and 1300.degree. C. or less. A heat treatment temperature of
1000.degree. C. or more forms a calcined product having the target
compositional ratio. A heat treatment temperature of 1400.degree.
C. or less may prevent decomposition of the calcined product,
yielding a nitride fluorescent material from the calcined product
without impairing the light emitting properties of the nitride
fluorescent material.
[0044] The heat treatment can also be performed as two-stage
calcination (multi-stage calcination) in which a first heat
treatment is performed at a temperature in a range of 800.degree.
C. or more and 1000.degree. C. or less, and the temperature is
gradually raised to perform a second heat treatment at a
temperature in a range of 1000.degree. C. or more and 1400.degree.
C. or less. The raw material mixture can be heat treated in a
crucible a board or the like composed of a material such as carbon
(such as graphite), boron nitride (BN), alumina (Ak.sub.2O.sub.3),
W, or Mo.
[0045] A preferred heat treatment atmosphere is an atmosphere
containing nitrogen gas. Besides nitrogen gas, the atmosphere
containing nitrogen gas may contain at least one selected from the
group consisting of hydrogen, argon, carbon dioxide, carbon
monoxide, ammonia, and the like. The proportion of nitrogen gas in
the heat treatment atmosphere is preferably 70% by volume or more,
more preferably 80% by volume or more.
[0046] The heat treatment is preferably performed in a pressurized
atmosphere in a range of 0.2 MPa or more and 200 MPa or less. The
target nitride fluorescent material more readily decomposes at a
higher temperature. Such a pressurized atmosphere can provide a
nitride fluorescent material having high light emitting properties
while preventing decomposition of the nitride fluorescent material.
The pressurized atmosphere is preferably in a range of 0.2 MPa or
more and 1.0 MPa or less, more preferably in a range of 0.8 MPa or
more and 1.0 MPa or less as gauge pressure. An increase in pressure
of the gas in the atmosphere during the heat treatment can prevent
decomposition of the fluorescent material compound during the heat
treatment to yield a fluorescent material having high light
emitting properties.
[0047] The time for the heat treatment can be appropriately
selected according to the heat treatment temperature, the pressure
of the gas, and the like. The time for the heat treatment is, for
example, in a range of 0.5 hours or more and 20 hours or less,
preferably in a range of 1 hour or more and 10 hours or less.
[0048] As one example of the production methods of the present
embodiment, a method of producing a calcined product includes a
designed composition Sr.sub.0.993Eu.sub.0.007LiAl.sub.3N.sub.4
among the nitride fluorescent material including the calcined
product having the compositions represented by the formula (I) will
now be specifically described. The method of producing a nitride
fluorescent material will not be limited to the production method
described below.
[0049] SrN.sub.u (where u=about 2/3, mixture of SrN.sub.2 and SrN),
LiAl.sub.4, AlN, and EuF.sub.3 powders are used as metal compounds
contained in the raw material mixture, and are weighed in a
glovebox having an inert atmosphere so as to have
Sr:Eu:Li:Al=0.9925:0.0075:1.2:3. These powders are mixed to prepare
a raw material mixture. At this time, Li is compounded in an amount
larger than its theoretical value because Li readily scatters
during calcination. The present embodiment will not be limited by
the compositional ratio.
[0050] The raw material mixture described above is heat treated in
the nitrogen atmosphere to obtain particles of calcined product
represented by Sr.sub.0.993Eu.sub.0.007LiAl.sub.3N.sub.4. A ratio
of each element in the compositional formula is a theoretical
composition ratio. Of the constituent elements, elements such as F
that may be partially scattered during calcination are not included
in the composition formula. As described above, the actual
composition contains a certain amount of elemental oxygen. With the
use of a fluoride that also can serve as a flux, a certain amount
of elemental fluoride can be contained in the calcined product. The
ratio of Sr, Eu, and Li in the composition formula is calculated
assuming the composition ratio of Al being 3. The ratio of Sr, Eu,
and Li in the charging ratio may be different from that in the
theoretical composition ratio because those components may be
scattered during the heat treatment. A nitride fluorescent material
with the target composition ratio can be obtained by varying the
compounding proportions of the raw materials.
[0051] The calcined product can also be produced by another method.
A calcined product having the target composition represented by the
formula (I) may be produced as follows: Metal single substances of
the elements are weighed so as to have a predetermined
compositional ratio, and are then melted into an alloy. The alloy
is then pulverized. The pulverized alloy is calcined in a nitrogen
gas atmosphere with a gas pressuring calcinating furnace, a hot
isostatic pressing (HIP) furnace using HIP, or the like.
Mixing Calcined Product with Polar Solvent
[0052] The production methods of the present embodiment each
includes a step of mixing the calcined product having a composition
represented by the formula (I) with a polar solvent. In the
production methods of the present embodiment, particles of the
calcined product are dispersed through the step of mixing the
calcined product including a composition represented by the formula
(I) with a polar solvent. It is considered that, in the process, at
least part of surfaces of the particles of the calcined product are
affected by the polar solvent and as a result, hydroxides and/or
oxides, for example, will be formed on the surfaces of the
particles of the calcined product. It can be believed that at least
part of the surface of the resulting phosphor contains a compound
having a composition different from the composition of the
fluorescent material and the refractive index of the phosphor near
the surfaces of fluorescent material particles is thus controlled,
resulting in increased efficiency in extraction of light, and a
light emission intensity from the fluorescent material is thus
enhanced. The production methods of the present embodiment each
comprise a step of mixing particles of the calcined product
including a composition represented by the formula (I) with a polar
solvent. In such methods, dispersion of particles of the calcined
product and control of the refractive index on the surfaces of the
particles of the calcined product can be performed at the same
time, efficiently producing a nitride phosphor having a high light
emission intensity.
Polar Solvent
[0053] In the production methods according to the present
embodiment of the present invention, the polar solvent is a polar
solvent having a relative dielectric constant in a range of 10 or
more and 70 or less at 20.degree. C., or is alcohol and/or ketone
containing water in a range of 0.01% by mass or more and 12% by
mass or less. The polar solvent has a relative dielectric constant
of more preferably 10 or more, still more preferably 15 or more at
20.degree. C. The polar solvent preferably has a relative
dielectric constant of 35 or less at 20.degree. C. Even if the
polar solvent is alcohol and/or ketone including 0.01% by mass or
more and 12% by mass or less of water, the polar solvent preferably
has a relative dielectric constant of 10 or more and 35 or less at
20.degree. C. A polar solvent having a relative dielectric constant
of less than 10 at 20.degree. C. is not preferred because such a
polar solvent has low affinity with water, resulting in poor
reaction between the surfaces of the fluorescent material particles
and water and a reduction in dispersibility of the calcined
product. A polar solvent having a relative dielectric constant of
more than 70 at 20.degree. C. is not preferred because such a polar
solvent has excessively high affinity with water and thus
decomposition of the calcined product (fluorescent material) tends
to proceed as a result of a reaction with water.
[0054] Examples of the polar solvent having a relative dielectric
constant of 10 or more and 70 or less at 20.degree. C. include
ethyl acetate, tetrahydrofuran, N,N-dimethylformamide, dimethyl
sulfoxide, alcohols having a linear or branched alkyl group having
1 to 8 carbon atoms, carboxylic acids (such as formic acid and
acetic acid), and ketones (such as acetone). The polar solvent
having a relative dielectric constant of 10 or more and 70 or less
at 20.degree. C. is preferably alcohol and/or ketone.
[0055] If alcohol and/or ketone is used as the polar solvent,
preferred are lower alcohol and/or ketone having a linear or
branched alkyl group having 1 to 4 carbon atoms. The polar solvent
is more preferably at least one polar solvent selected from the
group consisting of methanol (relative dielectric constant: 33),
ethanol (relative dielectric constant: 24), 1-propanol (relative
dielectric constant: 20), 2-propanol (relative dielectric constant:
18), and acetone (relative dielectric constant: 21). These polar
solvents can be used alone or in combination of two or more.
[0056] In the production method of one embodiment, the polar
solvent may contain water having a relative dielectric constant of
80 at 20.degree. C. The content of water in the polar solvent
alcohol and/or ketone is 0.01% by mass or more and 12% by mass or
less. The content of water in the polar solvent having a relative
dielectric constant of 10 or more and 70 or less at 20.degree. C.
is preferably 0.01% by mass or more and 12% by mass or less. The
content of water in the polar solvent is more preferably 0.1% by
mass or more and 10% by mass or less. The fluorescent material
particles are usually dispersed with water in many cases. The
nitride fluorescent material including the calcined product having
a composition represented by the formula (I), however, tends to be
decomposed as a result of a reaction with water in the presence of
water exceeding a predetermined amount. In the production methods
of the present embodiment, a predetermined amount of water is
contained in the polar solvent to form a compound having a
composition different from the composition of the nitride
fluorescent material on at least part of the surfaces of the
particles of the calcined product while preventing decomposition of
the calcined product forming the fluorescent material particles. It
is believed that the refractive index of the fluorescent material
near the surfaces of the fluorescent material particles is
controlled, resulting in increased efficiency in extraction of
light to the outside of the fluorescent material particles, and a
light emission intensity from the fluorescent material can thus be
enhanced.
[0057] In the production methods of the present embodiment, the
particles of the calcined product are preferably stirred in the
polar solvent. The particles of the calcined product can be
dispersed through stirring of the calcined product in the polar
solvent. During stirring of the calcined product in the polar
solvent, a dispersion medium such as alumina balls or zirconia
balls may be added to promote dispersion of the particles of the
calcined product. It is believed that stirring of the calcined
product in the polar solvent forms hydroxides and/or oxides on at
least part of the surfaces of the particles of the calcined product
while the particles are being dispersed. While the polar solvent
enhances the light emitting properties of the nitride fluorescent
material, a non-polar solvent barely improves the light emitting
properties of the nitride fluorescent material. This is probably
because while a polar solvent containing water can form hydroxides
and/or oxides, for example, on at least part of the surfaces of the
fluorescent material particles, an a non-polar solvent has low
affinity with water and barely forms hydroxides and/or oxides by
water on the surfaces of the fluorescent material particles.
Classifying
[0058] The production methods of the present embodiment each may
comprise a step of classifying a nitride fluorescent material to
yield a nitride fluorescent material having an average particle
size of 4.0 .mu.m or more after the step of mixing the calcined
product with the polar solvent. The classification step can control
the average particle size of the nitride fluorescent material to a
predetermined value or higher, yielding a nitride fluorescent
material having more enhanced absorptivity of excited light by the
nitride fluorescent material and light emission intensity. In the
classification step, specifically, a nitride fluorescent material
having an average particle size of 4.0 .mu.m or more can be
obtained with a method such as sieving, sediment classification in
a solution using gravity, or centrifugation. According to the
production methods of the present embodiment, a nitride fluorescent
material having an average particle size of preferably 4.0 to 20
.mu.m, more preferably 5.0 to 18 .mu.m is obtained through the
classification step.
[0059] Specific examples of the nitride fluorescent material
obtained by the production methods of the present embodiment will
be described below. The nitride fluorescent materials obtained by
the production methods of the present embodiment each comprise a
composition represented by formula (I). In the nitride fluorescent
materials obtained by the production methods of the present
embodiment, the content of elemental oxygen in the nitride
fluorescent material is 2% by mass or more and 4% by mass or less.
The nitride fluorescent materials contain the elemental oxygen
contained in the hydroxides and/or oxides thought to be formed
through mixing of the calcined product with the polar solvent, and
may additionally contain the elemental oxygen derived from
hydroxides and/or oxides formed on the surfaces of the fluorescent
material particles left in the air. It is inferred that extremely
slight amounts of hydroxides and/or oxides are generated after the
fluorescent material particles are left in the air. The nitride
fluorescent materials obtained by the production methods of the
present embodiment each comprise a composition represented by
formula (I), and may further contain elemental fluorine. It is
believed that the fluorine contained in the nitride fluorescent
materials is derived from the raw material mixture or the flux
described above.
Nitride Fluorescent Material
[0060] The nitride fluorescent material according to one embodiment
of the present invention include a calcined product having a
composition represented by following formula (I):
M.sup.a.sub.vM.sup.b.sub.wM.sup.c.sub.xM.sup.d.sub.yN.sub.z (I)
wherein M.sup.a is at least one element selected from the group
consisting of Sr, Ca, Ba, and Mg; M.sup.b is at least one element
selected from the group consisting of Li, Na, and K; M.sup.c is at
least one element selected from the group consisting of Eu, Mn, Tb,
and Ce; M.sup.d is at least one element selected from the group
consisting of Al, Si, B, Ga, In, Ge, and Sn, particularly
preferably at least one element selected from the group consisting
of Al, B, Ga, and In; v, w, x, y, and z are numbers satisfying
0.8.ltoreq.v.ltoreq.1.1, 0.8.ltoreq.w.ltoreq.1.1,
0.001<x.ltoreq.0.1, 2.0.ltoreq.y.ltoreq.4.0, and
3.0.ltoreq.z.ltoreq.5.0, respectively, and having a content of
elemental oxygen in a range of 2% by mass or more and 4% by mass or
less.
[0061] Although not shown in the formula (I), the nitride
fluorescent materials according to the present embodiment contain
elemental oxygen. It is believed that the elemental oxygen
contained in the nitride fluorescent materials according to the
present embodiment is mainly derived from hydroxides and/or oxides
formed on at least part of the surfaces of the particles of the
calcined product through mixing the particles of the calcined
product with the polar solvent. The nitride fluorescent materials
according to the present embodiment may contain elemental oxygen
derived from hydroxides and/or oxides formed on the surfaces of the
fluorescent material particles left in the air. Extremely slight
amounts of hydroxides and/or oxides are generated after the
fluorescent material particles are left in the air. The elemental
oxygens in the nitride fluorescent material not shown in the
composition represented by the formula (I) may be derived from
sources as below:
[0062] (1) slight amounts of hydroxides and/or oxides contained in
various nitrides, hydrides, metals, and the like used in the raw
material mixture,
[0063] (2) oxides generated through oxidation of the raw material
mixture during the heat treatment, and
[0064] (3) adherents to the nitride fluorescent material after
generation.
The elemental oxygen derived from the oxides or the adherents
derived from the sources (1) to (3) is contained in an extremely
slight amount. The elemental oxygen contained in the nitride
fluorescent material of the present embodiment, the elemental
oxygen derived from the sources (1) to (3) is contained in an
extremely slight amount of less than 0.1% by mass.
[0065] In a nitride fluorescent material where oxygen is present,
usually, control of the molar ratio of oxygen can change the
crystal structure of the fluorescent material to shift the peak
fluorescence wavelength of the fluorescent material. From the
viewpoint of the higher light emission intensity, however,
preferred is a smaller amount of oxygen contained in the nitride
fluorescent material. A larger amount of oxygen contained in the
nitride fluorescent material will affect not only the surfaces of
the fluorescent material particles but also the inside of the
fluorescent material particles, resulting in unstable crystal
structure of the nitride fluorescent material. Such unstable
crystal structure of the nitride fluorescent material tends to
reduce the light emission intensity. For this reason, in a nitride
fluorescent material containing oxygen, the elemental oxygen is
preferably contained near the surface of the nitride fluorescent
material.
[0066] The content of the elemental oxygen in the nitride
fluorescent material according to the present embodiment is 2% by
mass or more and 4% by mass or less. The content of the elemental
oxygen in the nitride fluorescent material is preferably in a range
of 2.2% by mass or more and 3.8% by mass or less, more preferably
in a range of 2.5% by mass or more and 3.5% by mass or less. The
elemental oxygen contained in an amount of more than 4% by mass in
the nitride fluorescent material increases the content of oxygen,
which will affect not only the surfaces of the fluorescent material
particles but also the inside of the fluorescent material
particles, and tends to reduce the light emission intensity. In
contrast, it is believed that the elemental oxygen contained in an
amount of less than 2% by mass in the nitride fluorescent material
cannot form sufficient hydroxides and/or oxides required for an
enhancement in extraction of light to the outside of the
fluorescent material particles near the surfaces of the fluorescent
material particles, and an enhancement in light emission intensity
of the nitride fluorescent material tends to be difficult.
[0067] The nitride fluorescent material according to the present
embodiment may further contain elemental fluorine. The content of
the elemental fluorine is preferably in a range of 0.1% by mass or
more and 1% by mass or less. The content of the elemental fluorine
contained in the nitride fluorescent material is more preferably
0.2% by mass or more and 0.8% by mass or less, still more
preferably 0.3% by mass or more and 0.7% by mass or less. It is
inferred that the elemental fluorine contained in the nitride
fluorescent material is derived from the raw material mixture or
the flux described above.
[0068] A content of the elemental fluorine in the nitride
fluorescent material of 0.1% by mass or more and 1% by mass or less
can reduce possibilities that another compound is present in the
nitride fluorescent material due to partial decomposition of the
nitride fluorescent material, preventing a reduction in light
emission intensity of the nitride fluorescent material caused by
the presence of another compound.
[0069] The nitride fluorescent material according to the present
embodiment have an internal quantum efficiency of preferably 80% or
more, more preferably 81% or more. Such an internal quantum
efficiency can enhance the light emission intensity of the nitride
fluorescent material.
[0070] The nitride fluorescent material according to the present
embodiment have an external quantum efficiency of preferably more
than 55%, more preferably of 56% or more. Such an external quantum
efficiency can enhance the light emission intensity of the nitride
fluorescent material.
[0071] In formula (I), M.sup.a preferably contains at least one of
Ca and Sr in view of enhancement of the light emission intensity of
the nitride fluorescent material. If M.sup.a contains at least one
of Ca and Sr, the total molar ratio of Ca and Sr contained in
M.sup.a is, for example, 85 mol % or more, preferably 90 mol % or
more. In formula (I), M.sup.b preferably contains at least Li in
view of the stability of the crystal structure. If M.sup.b contains
Li, the molar ratio of Li contained in M.sup.b is, for example, 80
mol % or more, preferably 90 mol % or more. Furthermore, it is
preferred in formula (I) that M.sup.c is Eu and M.sup.d is Al. In
formula (I), if M.sup.c is Eu and M.sup.d is Al, a nitride
fluorescent material having a narrow half bandwidth in the light
emission spectrum and a desired wavelength region can be
obtained.
[0072] In formula (I), v, w, x, y, and z can be any number as long
as the numeric value ranges shown above are satisfied. v and w are
preferably in a range of 0.8 or more and 1.1 or less and in a range
of 0.9 or more and 1.05 or less, respectively, in view of the
stability of the crystal structure. x is an Eu activating amount,
which may be appropriately selected so as to achieve desired
properties. x is a number satisfying 0.001<x.ltoreq.0.1,
preferably 0.001<x.ltoreq.0.02, more preferably
0.002.ltoreq.x.ltoreq.0.015. y is a number satisfying
2.0.ltoreq.y.ltoreq.4.0, preferably 2.0.ltoreq.y.ltoreq.3.5 in view
of the stability of the crystal structure. z is also a number
satisfying 3.0.ltoreq.z.ltoreq.5.0, preferably
3.0.ltoreq.z.ltoreq.4.0 in view of the stability of the crystal
structure.
[0073] The nitride fluorescent material according to the present
embodiment may contain impurities not shown in the composition
represented by formula (I). Such impurities that may be present in
the nitride fluorescent material are selected from the group
consisting of Sc, Y, Ti, Zr, V, Nb, Cr, Mo, Mn, Fe, Ru, Sm, Gd, Tb,
Dy, Ho, Er, Tm, Yb, Hf, Ta, W, Re, Os, Ir, Pt, Tl, Pb, and Bi.
[0074] The nitride fluorescent material according to the present
embodiment absorb light at a wavelength in a range of 400 nm or
more and 570 nm or less, which corresponds to ultraviolet light to
visible light in a shorter wavelength region, and emit fluorescence
having a peak fluorescence wavelength in a range of 630 nm or more
and 670 nm or less. A fluorescent material having a high light
emission intensity can be provided with an excitation light source
having a wavelength in this range. The excitation light source used
has a main peak light emission wavelength preferably at 420 nm or
more and 500 nm or less, more preferably 420 nm or more and 460 nm
or less.
[0075] The light emission spectrum of the nitride fluorescent
material has a peak fluorescence wavelength in a range of 630 nm or
more and 670 nm or less, preferably 640 nm or more and 660 nm or
less. The half bandwidth in the light emission spectrum is, for
example, 65 nm or less, preferably 60 nm or less. The lower limit
of the half bandwidth is 45 nm or more, for example.
[0076] The nitride fluorescent material has a light emission center
M.sup.c. If M.sup.c is europium (Eu), which is one of rare earth
elements, europium (Eu) is the center of light emission. In the
present embodiment, the center of light emission is not limited to
only europium. Europium in the center of light emission may
partially be replaced with another rare earth metal element or an
alkaline earth metal element. Europium and another element can be
used as a co-activator. A divalent rare earth element ion Eu.sup.2+
stably emits light by appropriate selection of a matrix
crystal.
[0077] The nitride fluorescent material has an average particle
size of, for example, 4.0 .mu.m or more, preferably 4.5 .mu.m or
more, more preferably 5.0 .mu.m or more. The average particle size
is, for example, 20 .mu.m or less, preferably 18 .mu.m or less.
[0078] An average particle size of a predetermined value or greater
tends to provide a nitride fluorescent material having enhanced
absorptivity of excited light and having enhanced light emission
intensity. As above, a nitride fluorescent material having a high
light emitting properties contained in a light-emitting device
described later enhances the light emission efficiency of the
light-emitting device. An average particle size of a predetermined
value or smaller can enhance the workability during the steps of
producing a light-emitting device.
[0079] Fluorescent material particles having the average particle
size are preferably contained in the nitride fluorescent material
with a high frequency. In other words, the nitride fluorescent
material preferably has narrow particle size distribution. By using
a fluorescent material having small variations in size of
particles, a light-emitting device having reduced color unevenness
and a good color tone can be obtained.
[0080] Throughout the specification, the average particle size of
the nitride fluorescent material and the average particle sizes of
other fluorescent materials are volume average particle sizes
(median particle sizes) measured with a laser diffraction particle
size distribution analyzer (MASTER SIZER 2000 made by Malvern
Instruments Ltd.).
[0081] The nitride fluorescent material preferably has a crystal
structure in most part of the particles. For example, a glass
(amorphous) material has a loose structure so that the composition
ratio in the fluorescent material may not be constant, which may
lead to uneven chromaticity. To avoid this, it is necessary arises
to control the reaction conditions in the manufacturing process to
avoid the above. The fluorescent material having a crystal
structure in most part of the particles facilitates production and
processing. Such a nitride fluorescent material is readily
uniformly dispersed in a resin, and therefore can facilitate
formation of a sealing member described later. The content of the
crystal structure in the fluorescent material particles shows the
percentage of crystalline phase which has luminescent properties.
The fluorescent material has crystalline phase of at least 50% by
mass or more, more preferably 80% by mass or more. Emission
sufficient for practical application can be obtained with the
content of crystal phase of 50% by mass or more.
Light-Emitting Device
[0082] A light-emitting device including the nitride fluorescent
material as a wavelength converting member will now be described.
The light-emitting device according to an embodiment of the present
invention comprises the nitride fluorescent material and an
excitation light source. The excitation light source preferably
emits light at a wavelength in a range of 400 nm or more and 570 nm
or less.
[0083] The excitation light source can use a light-emitting
element. The light-emitting element emits light at a wavelength in
a range of 400 nm or more and 570 nm or less. The peak light
emission wavelength of the light-emitting element lies preferably
in the wavelength range of 420 nm or more and 460 nm or less. Using
a light-emitting element having a peak light emission wavelength in
this range as an excitation light source yields a light-emitting
device that emits light resulting from a mix of the light from the
light-emitting element and the fluorescence from the fluorescent
materials. Because this allows effective use of a part of the light
radiated from the light-emitting element to the outside as light
for the light-emitting device, therefore achieving a light-emitting
device having a high light emission efficiency can be obtained.
[0084] A preferred light-emitting element to be used is, for
example, a semiconductor light-emitting element including a nitride
semiconductor (In.sub.XAl.sub.YGa.sub.1-X-YN, where 0.ltoreq.X,
0.ltoreq.Y, X+Y.ltoreq.1), which emits of blue or green light.
Using a semiconductor light-emitting element as an excitation light
source provides a highly efficient light emitting device that has
high linearity to the input, and is resistant and stable to
mechanical impact. The half bandwidth of the light emission
spectrum of the light emitting element can be 30 nm or less, for
example.
[0085] A first fluorescent material contained in the light-emitting
device comprises the nitride fluorescent material. The nitride
fluorescent material comprise the composition represented by the
formula (I), is excited by light at a wavelength in a range of 400
nm or more and 570 nm or less, and has a peak light emission
wavelength in a range of 630 nm or more and 670 nm or less.
[0086] The first fluorescent material, contained in a sealing resin
covering the excitation light source, for example, can constitute
the light-emitting device. In the light-emitting device including
an excitation light source covered with an sealing resin containing
the first fluorescent material, light emitted from the excitation
light source is partially absorbed by the first fluorescent
material, and red light is emitted. More effective use of the
emitted light is enabled by using an excitation light source
emitting light at a wavelength in a range of 400 nm or more and 570
nm or less. As a result, the loss of light emitted from the
light-emitting device can be reduced, providing a light-emitting
device having a high light emission efficiency.
[0087] The content of the first fluorescent material contained in
the light-emitting device can be, for example, from 1 part by mass
to 50 parts by mass, preferably from 2 parts by mass to 30 parts by
mass relative to 100 parts by mass of the sealing resin.
[0088] The light-emitting device may incorporate a second
fluorescent material that has a range of a peak fluorescence
wavelength different from that of the first fluorescent material.
For example, the light-emitting device incorporating a
light-emitting element emitting blue light and the first
fluorescent material and the second fluorescent material excited by
the blue light from the light-emitting element can be achieved a
wide range of color reproducibility and good color rendering.
[0089] Examples of the second fluorescent material can include
fluorescent materials having a compositions represented by any one
of the following formulae (IIa), (IIb), (IIc), (IId), (IIe), (IIf),
(IIg), (IIh) and (IIi). For example, the second fluorescent
material more preferably contains at least one fluorescent material
having a composition represented by one formula selected from
formulae (IIc), (IIe), (IIh) and (IIi) to achieve a wide range
color reproducibility.
(Y,Gd,Tb,Lu).sub.3(Al,Ga).sub.5O.sub.12:Ce (IIa)
(Ba,Sr,Ca).sub.2SiO.sub.4:Eu (IIb)
Si.sub.6-pAl.sub.pO.sub.pN.sub.8-p:Eu (where 0<p.ltoreq.4.2)
(IIc)
(Ca,Sr).sub.8MgSi.sub.4O.sub.16(Cl,F,Br).sub.2:Eu (IId)
(Ba,Sr,Ca)Ga.sub.2S.sub.4:Eu (IIe)
(Ba,Sr,Ca).sub.2Si.sub.5N.sub.8:Eu (IIf)
(Sr,Ca)AlSiN.sub.3:Eu (IIg)
K.sub.2(Si,Ge,Ti)F.sub.6:Mn (IIh)
(Ba,Sr)MgAl.sub.10O.sub.17:Mn (IIi)
[0090] The second fluorescent material has an average particle size
in a range of preferably 2 .mu.m or more and 35 .mu.m or less, more
preferably 5 .mu.m or more and 30 .mu.m or less. An average
particle size having a predetermined value or greater can more
significantly enhance the light emission intensity from the second
fluorescent material. An average particle size having a
predetermined value or less can enhance the workability during the
steps of producing the light-emitting device.
[0091] The amount of the second fluorescent material may be
appropriately selected according to the purpose. The amount of the
second fluorescent material may be, for example, from 1 part by
mass to 200 parts by mass, preferably from 2 parts by mass to 180
parts by mass relative to 100 parts by mass of the sealing
resin.
[0092] The ratio of the first fluorescent material to the second
fluorescent material (first fluorescent material/second fluorescent
material) may be 0.01 to 5, preferably 0.05 to 3 in mass ratio.
[0093] The first fluorescent material and the second fluorescent
material (hereinafter, also collectively simply referred to as
"fluorescent material") with the sealing resin preferably form a
sealing member covering the light-emitting element. Examples of the
sealing resin contained in the sealing member may include epoxy
resins and silicone resins.
[0094] The total content of the fluorescent materials in the
sealing member may be, for example, from 5 parts by mass to 300
parts by mass, preferably from 10 parts by mass to 250 parts by
mass, more preferably from 15 parts by mass to 230 parts by mass,
still more preferably from 15 parts by mass to 200 parts by mass
relative to 100 parts by mass of the sealing resin.
[0095] Besides the sealing resin and the fluorescent materials, the
sealing member may further contain a filler, a light diffusing
material, and the like. Examples of the filler and the light
diffusing material can include silica, titanium oxide, zinc oxide,
zirconium oxide, and alumina. In a sealing member containing a
filler, the content can be appropriately selected according to the
purpose, etc. The amount of the filler may be from 1 part by mass
to 20 parts by mass relative to 100 parts by mass of the sealing
resin, for example.
[0096] An example of the light-emitting device according to the
present embodiment will be described with reference to the drawing.
FIG. 1 is a schematic cross-sectional view of an exemplary
light-emitting device according to the present embodiment.
[0097] A light-emitting device 100 includes a package 40 having a
recessed part, a light-emitting element 10, and a sealing member 50
covering the light-emitting element 10. The light-emitting element
10 is disposed in the recessed part formed in the package 40, and
is electrically connected through a conductive wire 60 to a pair of
positive and negative lead electrodes 20 and 30 disposed in the
package 40. The sealing member 50 is formed of a sealing resin
containing a fluorescent material 70 and filled into the depressed
portion to cover the light-emitting element 10. The sealing member
50 comprises a sealing resin, and a fluorescent material 70
converting the wavelength of light from the light-emitting element
10, for example. Furthermore, the fluorescent material 70 contains
a first fluorescent material 71 and a second fluorescent material
72. The pair of positive and negative lead electrodes 20 and 30 is
partially exposed to the exterior surfaces of the package 40. The
light-emitting device 100 emits light as a result of receiving
external electricity through these lead electrodes 20 and 30 to the
light-emitting device 100.
[0098] The sealing member 50 functions not only as a wavelength
converting member but also a member protecting the light-emitting
element 10, the first fluorescent material 71, and the second
fluorescent material 72 from an external environment. In FIG. 1,
the first fluorescent material 71 and the second fluorescent
material 72 are lopsided in the sealing member 50. Arranging the
first fluorescent material 71 and the second fluorescent material
72 disposed close to the light-emitting element 10, as illustrated,
enables efficient wavelength conversion of the light from the
light-emitting element 10, and the light-emitting device of
excellent luminous efficiency can be obtained. The arrangement of
the sealing member 50 containing the first fluorescent material 71
and the second fluorescent material 72 and the light-emitting
element 10 will not be limited to the arrangement where the first
fluorescent material 71 and the second fluorescent material 72 are
disposed close to the light-emitting element 10. Considering
influences on the first fluorescent material 71 and the second
fluorescent material 72 by heat, the first fluorescent material 71
and the second fluorescent material 72 can be arranged spaced from
the light-emitting element 10 in the sealing member 50. The first
fluorescent material 71 and the second fluorescent material 72 can
also be almost homogeneously dispersed all over the sealing member
50 to generate light having reduced unevenness of color.
EXAMPLES
[0099] The present invention will be more specifically described by
way of Examples, but the present invention will not be limited to
these Examples.
Production Example 1
[0100] To yield a nitride fluorescent material including a calcined
product having a composition represented by
M.sup.a.sub.vM.sup.b.sub.wM.sup.c.sub.xM.sup.d.sub.yN.sub.z where
M.sup.a was Sr, M.sup.b was Li, M.sup.c was Eu, and M.sup.d was Al,
raw materials SrN, (where u=about 2/3, mixture of SrN.sub.2 and
SrN), SrF.sub.2, LiAlH.sub.4, AlN, and EuF.sub.3 were used. These
raw materials were weighed in a glovebox in an inert atmosphere so
as to have a molar ratio Sr:Li:Eu:Al=0.9925:1.2:0.0075:3 as the
ratio of the amounts of prepared, and were mixed to prepare a raw
material mixture. At this point, the mass ratio of SrN.sub.u to
SrF.sub.2 was set to 94:6. An amount of Li larger than that in the
target composition was compounded because Li readily scatters
during calcination. The raw material mixture was charged into a
crucible, and was heat treated for three hours in a nitrogen gas
atmosphere at a gas pressure (gauge pressure) of 0.92 MPa (absolute
pressure of 1.02 MPa) and a temperature of 1100.degree. C. to yield
powdery calcined product 1.
Example 1
[0101] 30 g of the calcined product 1 obtained in Production
Example 1 was added to 80 ml of ethanol (purity: 99.5% or more,
relative dielectric constant at 20.degree. C.: 24, moisture
content: 0.03% by mass), and was stirred for three hours. After
stirring, coarse particles and microfine particles were removed
through classification. The resulting particles were dried to yield
a nitride fluorescent material of Example 1 having an adjusted
average particle size (Dm) shown in Table 1.
Comparative Example 1
[0102] The calcined product 1 prepared in Production Example 1 was
used as the nitride fluorescent material of Comparative Example
1.
Example 2
[0103] A nitride fluorescent material of Example 2 was prepared on
the same conditions as those in Example 1 except that pure water
was added such that the content of water in ethanol was 1% by
mass.
Example 3
[0104] A nitride fluorescent material of Example 3 was prepared on
the same conditions as those in Example 1 except that pure water
was added such that the content of water in ethanol was 5% by
mass.
Example 4
[0105] A nitride fluorescent material of Example 4 was prepared on
the same conditions as those in Example 1 except that pure water
was added such that the content of water in ethanol was 10% by
mass.
Comparative Example 2
[0106] A nitride fluorescent material of Comparative Example 2 was
prepared on the same conditions as those in Example 1 except that
pure water was added such that the content of water in ethanol was
12.5% by mass.
Comparative Example 3
[0107] A nitride fluorescent material of Comparative Example 3 was
prepared on the same conditions as those in Example 1 except that
pure water was added such that the content of water in ethanol was
15.0% by mass.
Comparative Example 4
[0108] A nitride fluorescent material of Comparative Example 4 was
prepared on the same conditions as those in Example 1 except that
pure water was added such that the content of water in ethanol was
17.5% by mass.
Comparative Example 5
[0109] A nitride fluorescent material of Comparative Example 5 was
prepared on the same conditions as those in Example 1 except that
pure water was added such that the content of water in ethanol was
20% by mass.
Comparative Example 6
[0110] A nitride fluorescent material of Comparative Example 6 was
prepared on the same conditions as those in Example 1 except that
pure water was added such that the content of water in ethanol was
50% by mass.
Example 5
[0111] A nitride fluorescent material of Example 5 was prepared on
the same conditions as those in Example 1 except that ethanol was
replaced with 2-propanol (purity: 99.7% or more, relative
dielectric constant at 20.degree. C.: 18, moisture content: 0.11%
by mass).
Comparative Example 7
[0112] A nitride fluorescent material of Comparative Example 7 was
prepared on the same conditions as those in Example 1 except that
ethanol was replaced with hexane (purity: 96% or more, relative
dielectric constant at 20.degree. C.: 2, moisture content: less
than 0.01% by mass).
Evaluation
X-Ray Diffraction Spectrum
[0113] The nitride fluorescent materials prepared above were
measured to obtain the X-ray diffraction spectra (XRD). The
measurement was performed with a sample leveling type multi-purpose
X-ray diffraction apparatus (product name: UltimaIV, manufactured
by Rigaku Corporation) using CuK.alpha. rays. The examples of the
resulting XRD patterns are shown in FIG. 2.
Average Particle Size
[0114] The average particle sizes of the nitride fluorescent
material prepared above were measured with a laser diffraction
particle size distribution analyzer (MASTER SIZER 2000 manufactured
by MALVERN Instruments Ltd.). The results are shown in Table 1.
Light Emitting Properties
[0115] The light emitting properties of the nitride fluorescent
material prepared above were measured. The light emitting
properties of the powder of the nitride fluorescent material were
measured with a spectrofluorometer QE-2000 (manufactured by Otsuka
Electronics Co., Ltd.) using excited light having a wavelength of
450 nm. From the light emission spectra obtained in the
measurement, the relative light emission intensity Ip (%), the peak
fluorescence wavelength .lamda.p (nm), the internal quantum
efficiency (%), and the external quantum efficiency (%) were
determined. The results are shown in Table 1. The relative light
emission intensity Ip (%) was calculated where the nitride
fluorescent material of Comparative Example 1 was used as the
reference. FIG. 3 illustrates the light emission spectra of the
nitride fluorescent material prepared in Comparative Example 1 and
Example 1. In FIG. 3, each light emission spectrum represents a
relative light emission intensity to the wavelength.
Compositional Analysis
[0116] The composition ratios (molar ratio) of elements Sr, Li, Eu,
Al and N of the nitride fluorescent material prepared above were
measured with an inductively coupled plasma light emission analyzer
(manufactured by PerkinElmer Inc.) by ICP light emission analysis.
The amounts (% by mass) of O and F of the nitride fluorescent
material prepared above were measured with an oxygen-nitrogen
analyzer manufactured by HORIBA, Ltd. The results are shown in
Table 2. The compositional ratio (mole ratio) of each element was a
value obtained by calculating when the composition ratio (mole
ratio) of Al, which is 3, as a reference.
SEM Images
[0117] SEM images of the nitride fluorescent material of Example 1,
Example 4, and Comparative Example 6 were obtained with a scanning
electron microscope (SEM). FIG. 4 is an SEM image of the nitride
fluorescent material of Example 1; FIG. 5 is an SEM image of the
nitride fluorescent material of Example 4; and FIG. 6 is an SEM
image of the nitride fluorescent material of Comparative Example
6.
TABLE-US-00001 TABLE 1 Relative Moisture Average Peak light
Internal External content: particle fluorescence emission quantum
quantum Organic (% by size Dm wavelength intensity efficiency
efficiency solvent mass) (.mu.m) .lamda.p (nm) Ip (%) (IQE) (%)
(EQE) (%) Comparative None -- 20.8 656 100.0 77.0 55.0 Example 1
Example 1 Ethanol 0.03 9.1 656 110.1 81.7 58.7 Example 2 1.00 8.9
656 108.1 82.3 58.9 Example 3 5.00 8.8 656 110.2 83.0 60.5 Example
4 10.00 8.7 656 109.4 82.9 59.8 Comparative 12.50 8.7 654 96.8 85.8
53.3 Example 2 Comparative 15.00 7.7 654 88.9 85.5 49.2 Example 3
Comparative 17.50 9.5 654 95.3 83.8 51.6 Example 4 Comparative
20.00 9.8 652 96.6 79.4 50.2 Example 5 Comparative 50.00 17.1 652
72.0 68.8 39.5 Example 6 Example 5 2-Propanol 0.11 8.8 656 109.7
81.9 58.3 Comparative Hexane <0.01 10.4 656 100.8 79.0 54.9
Example 7
TABLE-US-00002 TABLE 2 Compositional ratio (mole ratio) Mass ratio
(% by mass) Sr Eu Li Al N O F Comparative 1.019 0.007 1.032 3.000
3.527 1.65 0.65 Example 1 Example 1 1.001 0.007 1.013 3.000 3.568
2.86 0.52 Example 2 1.012 0.007 1.037 3.000 3.569 3.27 0.53 Example
3 0.988 0.007 1.016 3.000 3.572 2.60 0.50 Example 4 1.005 0.007
0.993 3.000 3.500 3.42 0.52 Comparative 1.074 0.008 1.086 3.000
2.679 12.18 0.01 Example 2 Comparative 1.095 0.008 1.081 3.000
1.820 19.00 0.01 Example 3 Comparative 1.072 0.008 1.084 3.000
2.172 17.95 0.01 Example 4 Comparative 1.035 0.007 1.060 3.000
2.018 16.82 0.07 Example 5 Comparative 1.082 0.008 1.023 3.000
1.011 19.14 0.07 Example 6 Example 5 1.001 0.007 1.013 3.000 3.521
2.53 0.50 Comparative 1.020 0.007 1.067 3.000 3.260 5.81 0.46
Example 7
[0118] The results of the relative light emission intensity shown
in Table 1 show that Examples 1 to 5 each have a relative light
emission intensity higher than that of Comparative Example 1. The
light emission spectra shown in FIG. 3 show that Example 1 has a
relative light emission intensity higher than that of Comparative
Example 1. Table 1 also shows that the internal quantum
efficiencies of Examples 1 to 5 are each 80% or more, and are
higher than those of Comparative Examples 1 and 5 to 7. The
external quantum efficiencies of Examples 1 to 5 are each 58% or
more, and are higher than those of Comparative Examples. Examples 1
to 5 have enhanced light conversion efficiency. Using these
fluorescent material in light-emitting devices can provide
light-emitting devices generating higher luminous flux. In
Comparative Examples 2 to 4 using the polar solvent in which the
content of water was more than 12% by mass, the external quantum
efficiency was 55% or less, and the relative light emission
intensity was reduced. As shown in Comparative Examples 5 and 6, it
is inferred that a content of water of 20% by mass or more in the
polar solvent proceeds decomposition of fluorescent material
particles with water. The internal quantum efficiency was less than
80%, and the external quantum efficiency was 55% or less. The light
conversion efficiency and the relative light emission intensity
were also reduced.
[0119] FIG. 2 sequentially illustrates the XRD patterns of
Comparative Example 1, Comparative Example 5, Comparative Example
6, Comparative Example 7, Example 1, Example 4, Example 5, and as
references, Sr.sub.3Al.sub.2(OH).sub.12,
LiAl.sub.2(OH).sub.7.2H.sub.2O, and a compound (SLAN) represented
by SrLiAl.sub.3N.sub.4. The XRD patterns shown in FIG. 2 confirmed
that the compounds of Comparative Examples 1 and 5 to 7 and
Examples 1, 4, and 5 had XRD patterns similar to the XRD pattern of
SLAN, and these compounds all comprise a composition represented by
SrLiAl.sub.3N.sub.4. In Comparative Examples 5 and 6, in addition
to SrLiAl.sub.3N.sub.4, peaks derived from
Sr.sub.3Al.sub.2(OH).sub.12, LiAl.sub.2(OH).sub.7.2H.sub.2O, etc.
were present. This suggests that the fluorescent material particles
were partially decomposed. As shown in FIG. 2, in Comparative
Examples 5 and 6, a small amount of a different compound was
present in addition to SrLiAl.sub.3N.sub.4. For this reason, it is
believed that the target compounds were partially decomposed to
reduce the relative light emission intensity and the internal
quantum efficiency. In Comparative Example 7, ethanol was replaced
with hexane having a relative dielectric constant at 20.degree. C.
of 2. The relative light emission intensity in Comparative Example
7 was not as high as those of Examples 1 to 5, and the internal
quantum efficiency was similar to those of other Comparative
Examples. The light emitting properties were not improved.
[0120] The compositional ratios (mole ratio) of elements Sr, Li,
Eu, Al and N shown in Table 2 are values obtained by calculating
the composition ratio (mole ratio) Al, which is 3, as a reference.
The ratios of the oxygen (O) element and the fluorine (F) element
are represented as the mass ratio (% by mass). In Examples 1 to 5,
the content of the oxygen (O) element is larger than in Comparative
Example 1, and is 2 to 4% by mass. It is believed that the content
of the elemental oxygen in the fluorescent material particles is
increased because the calcined product particles were dispersed in
the polar solvent having a relative dielectric constant in a range
of 10 or more and 70 or less at 20.degree. C. to increase the
specific surface areas of the particles that come in contacted with
the polar solvent, and as a result, the surfaces of the fluorescent
material particles are strongly affected by the polar solvent. In
Examples 1 to 5, the compositional ratio (mole ratio) of Eu barely
changed from the ratio of the prepared amount, and he composition
ratios (mole ratios) of Sr and Li slightly changed from the ratios
of the prepared amounts. Although it is believed that Li relatively
significantly reduces from the prepared amount during the heat
treatment, the composition ratio (mole ratio) of the element Li in
the fluorescent material shows that the composition barely changed
by solvent treatment with the polar solvent. In Comparative
Examples 2 to 6, the nitride fluorescent material particles
partially decomposed as described in the X-ray diffraction spectrum
(XRD), because the calcined product particles were dispersed in the
polar solvent containing a relatively large amount of water. It is
believed that the fluorine (F) element contained in the calcined
product particles reacted with an excess water to remove the
elemental fluorine, and as a result, the content of the fluorine
(F) element was smaller than in Comparative Example 1.
[0121] Any apparently great difference cannot be found between the
SEM image of the nitride fluorescent material of Example 1 shown in
FIG. 4 and the SEM image of the nitride fluorescent material of
Example 4 shown in FIG. 5. In contrast, it is confirmed from the
SEM image of the nitride fluorescent material of Comparative
Example 6 shown in FIG. 6 that the nitride fluorescent material had
a rough surface. From comparison between the SEM images of FIG. 4
and FIG. 5 and the SEM image of FIG. 6, it is inferred that the
nitride fluorescent material of Example 1 and 4 had relatively
smooth surfaces while the nitride fluorescent material of
Comparative Example 6 in FIG. 6 had a rough surface because the
nitride fluorescent material partially decomposed.
[0122] The nitride fluorescent material of the present embodiment
have high light emission intensity. Use of these nitride
fluorescent material can provide light-emitting devices generating
higher luminous flux.
INDUSTRIAL APPLICABILITY
[0123] Light-emitting devices containing the nitride fluorescent
material according to the present disclosure can be suitably used
as light sources for lighting. These light-emitting devices can be
particularly suitably used in light sources for lighting including
light emitting diodes as excitation light sources and having
extremely high light emitting properties, LED displays, backlight
light sources for liquid crystal displays, traffic signals,
lighting switches, a variety of sensors, a variety of indicators,
and the like.
[0124] It is to be understood that although the present disclosure
has been described with regard to preferred embodiments thereof,
various other embodiments and variants may occur to those skilled
in the art, which are within the scope and spirit of the
disclosure, and such other embodiments and variants are intended to
be covered by the following claims.
[0125] All publications, patent applications, and technical
standards mentioned in this specification are herein incorporated
by reference to the same extent as if each individual publication,
patent application, or technical standard was specifically and
individually indicated to be incorporated by reference.
* * * * *