U.S. patent number 10,385,264 [Application Number 15/615,858] was granted by the patent office on 2019-08-20 for phosphor, method of producing same, and light-emitting device.
This patent grant is currently assigned to PANASONIC CORPORATION. The grantee listed for this patent is Panasonic Corporation. Invention is credited to Yoshihisa Nagasaki, Takashi Ohbayashi, Kojiro Okuyama.
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United States Patent |
10,385,264 |
Okuyama , et al. |
August 20, 2019 |
Phosphor, method of producing same, and light-emitting device
Abstract
A phosphor includes, as a main component, a compound represented
by a general formula
(3-a)YO.sub.3/2.aCeO.sub.3/2.(5-b)AlO.sub.3/2.bGaO.sub.3/2.cKO.sub.1/2.dP-
O.sub.5/2, where a, b, c and d satisfy 0.12.ltoreq.a.ltoreq.0.18,
1.50.ltoreq.b.ltoreq.3.00, 0.01.ltoreq.c.ltoreq.0.08, and
0.01.ltoreq.d.ltoreq.0.08.
Inventors: |
Okuyama; Kojiro (Nara,
JP), Nagasaki; Yoshihisa (Osaka, JP),
Ohbayashi; Takashi (Osaka, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Panasonic Corporation |
Osaka |
N/A |
JP |
|
|
Assignee: |
PANASONIC CORPORATION (Osaka,
JP)
|
Family
ID: |
60675333 |
Appl.
No.: |
15/615,858 |
Filed: |
June 7, 2017 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20170369775 A1 |
Dec 28, 2017 |
|
Foreign Application Priority Data
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|
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Jun 24, 2016 [JP] |
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2016-125672 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09K
11/7706 (20130101); H05B 33/14 (20130101); H01L
33/502 (20130101); C09K 11/0822 (20130101); C09K
11/621 (20130101); C09K 11/7721 (20130101); C09K
11/701 (20130101); H01L 51/50 (20130101); C09K
11/7723 (20130101); C09K 11/641 (20130101); C09K
11/7716 (20130101); C09K 11/7777 (20130101) |
Current International
Class: |
C09K
11/62 (20060101); C09K 11/70 (20060101); C09K
11/08 (20060101); C09K 11/77 (20060101); C09K
11/64 (20060101); H01L 33/50 (20100101); H01L
51/50 (20060101); H05B 33/14 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1998/005078 |
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Feb 1998 |
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WO |
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2013/118199 |
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Aug 2013 |
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WO |
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2013/118200 |
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Aug 2013 |
|
WO |
|
Other References
Edited by Keikoutaidougakukai, "Phosphor Handbook", Ohmsha, Ltd.,
p. 12, pp. 237-238, pp. 268-278, and p. 332, Dec. 1987. cited by
applicant.
|
Primary Examiner: Koslow; C Melissa
Attorney, Agent or Firm: McDermott Will & Emery LLP
Claims
What is claimed is:
1. A phosphor including, as a main component, a compound
represented by a general formula
(3-a)YO.sub.3/2.aCeO.sub.3/2.(5-b)AlO.sub.3/2.bGaO.sub.3/2.cKO.sub.1/2.dP-
O.sub.5/2, where a, b, c and d satisfy 0.12.ltoreq.a.ltoreq.0.18,
1.50.ltoreq.b.ltoreq.3.00, 0.01.ltoreq.c.ltoreq.0.08, and
0.01.ltoreq.d.ltoreq.0.08.
2. The phosphor according to claim 1, including the compound in an
amount of 70% by weight or more relative to the entire
phosphor.
3. The phosphor according to claim 1, including the compound in an
amount of 90% by weight or more relative to the entire
phosphor.
4. The phosphor according to claim 1, wherein the phosphor absorbs
light having a peak wavelength in a range of 380 to 420 nm to emit
light having a peak wavelength in a range of 530 to 550 nm.
5. A light-emitting device comprising: a phosphor including, as a
main component, a compound represented by a general formula
(3-a)YO.sub.3/2.aCeO.sub.3/2.(5-b)AlO.sub.3/2.bGaO.sub.3/2.cKO.sub.1/2.dP-
O.sub.5/2, where a, b, c and d satisfy 0.12.ltoreq.a.ltoreq.0.18,
1.50 b.ltoreq.3.00, 0.01.ltoreq.c.ltoreq.0.08, and
0.01.ltoreq.d.ltoreq.0.08; and an excitation light source which
emits first light having a peak wavelength in a range of 380 to 420
nm, wherein the phosphor absorbs part of the first light from the
excitation light source to emit second light having a longer
wavelength than the first light.
6. The light-emitting device according to claim 5, wherein the
phosphor includes the compound in an amount of 70% by weight or
more relative to the entire phosphor.
7. The light-emitting device according to claim 5, wherein the
phosphor includes the compound in an amount of 90% by weight or
more relative to the entire phosphor.
8. The light-emitting device according to claim 5, wherein the
second light is light having a peak wavelength in a range of 530 to
550 nm.
9. A method for producing a phosphor, the phosphor including, as a
main component, a compound represented by a general formula
(3-a)YO.sub.3/2.aCeO.sub.3/2.(5-b)AlO.sub.3/2.bGaO.sub.3/2.cKO.sub.1/2.dP-
O.sub.5/2, where a, b, c and d satisfy 0.12.ltoreq.a.ltoreq.0.18,
1.50.ltoreq.b.ltoreq.3.00, 0.01.ltoreq.c.ltoreq.0.08, and
0.01.ltoreq.d.ltoreq.0.08, the method comprising: preparing a
mixture which includes starting materials for the phosphor; and
firing the mixture in an atmosphere with an oxygen partial pressure
in a range of 10.sup.-6 to 10.sup.-3 atm.
10. The method according to claim 9, wherein the mixture includes,
as a reaction accelerator, a fluorine-containing compound.
11. The method according to claim 9, wherein the phosphor includes
the compound in an amount of 70% by weight or more relative to the
entire phosphor.
12. The method according to claim 9, wherein the phosphor includes
the compound in an amount of 90% by weight or more relative to the
entire phosphor.
13. The method according to claim 9, wherein the phosphor absorbs
light having a peak wavelength in a range of 380 to 420 nm to emit
light having a peak wavelength in a range of 530 to 550 nm.
Description
BACKGROUND
1. Technical Field
The present disclosure relates to a phosphor, a method of producing
the same, and a light-emitting device using a phosphor.
2. Description of the Related Art
The compound represented by the chemical formula
Y.sub.3Al.sub.5O.sub.12 is widely known under the name of yttrium
aluminum garnet and has been used in solid-state lasers,
translucent ceramics, and the like.
In particular, phosphors (YAG:Ce) in which cerium (Ce) ions serving
as luminescent centers are added to yttrium aluminum garnet are
known. It is known that YAG:Ce phosphors are excited by irradiation
with corpuscular beams, such as electron beams, or electromagnetic
waves, such as ultraviolet rays and blue light, and emit yellow to
green visible light. Therefore, YAG:Ce phosphors are broadly used
in various light-emitting devices (for example, refer to the
specification of Japanese Patent No. 3503139; the specification of
U.S. Pat. No. 6,812,500; and "Phosphor Handbook" edited by
Keikoutaidougakukai, Ohmsha, Ltd., p. 12, pp. 237-238, pp. 268-278,
and p. 332).
Yttrium aluminum garnet-type phosphors are used as yellow phosphors
in various light-emitting devices. Typical examples of such
light-emitting devices include a white light-emitting diode (LED)
in which a blue LED and a yellow phosphor are combined, a projector
using a blue laser diode (LD) and a phosphor, an illumination light
source using a blue-violet LD or blue-violet LED and a phosphor,
and a liquid crystal display (LCD) provided with an LED
backlight.
In particular, an illumination light source including a blue-violet
LD or blue-violet LED, a blue phosphor, and a yellow phosphor is
able to achieve high color rendering.
SUMMARY
One non-limiting and exemplary embodiment provides a phosphor which
can have high external quantum efficiency.
In one general aspect, the techniques disclosed here feature a
phosphor represented by a general formula
(3-a)YO.sub.3/2.aCeO.sub.3/2.(5-b)AlO.sub.3/2.bGaO.sub.3/2.cKO.sub.1/2.dP-
O.sub.5/2, where a, b, c and d satisfy 0.12.ltoreq.a.ltoreq.0.18,
1.50.ltoreq.b.ltoreq.3.00, 0.01.ltoreq.c.ltoreq.0.08, and
0.01.ltoreq.d.ltoreq.0.08.
A phosphor according to one aspect of the present disclosure can
have high external quantum efficiency.
It should be noted that general or specific embodiments may be
implemented as a phosphor, a device, a system, a method, or any
selective combination thereof.
Additional benefits and advantages of the disclosed embodiments
will become apparent from the specification and drawings. The
benefits and/or advantages may be individually obtained by the
various embodiments and features of the specification and drawings,
which need not all be provided in order to obtain one or more of
such benefits and/or advantages.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph showing the relationship between the addition
amount (a) of Ce in the general formula and the external quantum
efficiency and the relationship between the addition amount (a) of
Ce in the general formula and the chromaticity, with regard to
phosphor samples 9 to 11 of Example and phosphor samples 1 and 2 of
Comparative Example;
FIG. 2 is a graph showing the relationship between the addition
amount (b) of Ga in the general formula and the external quantum
efficiency and the relationship between the addition amount (b) of
Ga in the general formula and the chromaticity, with regard to
phosphor samples 10 and 16 to 21 of Example and phosphor samples 3
and 4 of Comparative Example;
FIG. 3 is a graph illustrating the relationship between the Ga
concentration and the luminescent chromaticity and the relationship
between the Ga concentration and the absorptance for blue-violet
light, with regard to YAG:Ce phosphors;
FIG. 4 is a graph illustrating the relationship between the Ce
concentration and the luminescent chromaticity and the relationship
between the Ce concentration and the internal quantum efficiency,
with regard to YAG:Ce phosphors; and
FIG. 5 is a graph showing an example of the relationship between
the oxygen partial pressure in the firing atmosphere and the
internal quantum efficiency of phosphors.
DETAILED DESCRIPTION
The knowledge on which the present disclosure is based will be
described below.
In YAG:Ce phosphors, the absorptance for blue-violet light with a
wavelength of about 405 nm is lower than the absorptance for blue
light with a wavelength of about 450 nm. Therefore, in the case
where blue-violet light is used as excitation light, it is
difficult to enhance the external quantum efficiency, which is the
product of the absorptance for excitation light (hereinafter, may
be simply abbreviated as the "absorptance") and the internal
quantum efficiency.
When aluminum (Al) is partially replaced by gallium (Ga) in a
YAG:Ce phosphor, the absorptance for blue-violet light can be
enhanced. However, increasing the addition amount of Ga shifts the
peak wavelength of light emitted from the phosphor toward the
shorter wavelength side, and it is not possible to obtain good
yellow light emission, which is a problem.
The present inventors conducted studies on the absorptance for
blue-violet light (wavelength: 405 nm) in YAG:Ce phosphors to which
Ga is added and on the chromaticity of light emitted from the
YAG:Ce phosphors in Experiment 1. The procedure and results thereof
will be described below.
In Experiment 1, a plurality of YAG:Ce phosphors represented by the
general formula
(3-a)YO.sub.3/2.aCeO.sub.3/2.(5-b)AlO.sub.3/2.bGaO.sub.3/2 were
produced by setting the addition amount (a) of Ce in the general
formula to be 0.06 and the addition amount (b) of Ga in the general
formula to be varied. The YAG:Ce phosphors were produced by firing
mixtures prepared by mixing starting materials at predetermined
ratios. The mixtures were fired in nitrogen gas which contained
hydrogen gas (hydrogen gas content: 2%) at a temperature of
1,600.degree. C. for 4 hours. Subsequently, the absorptance for
blue-violet light and luminescent chromaticity of the resulting
YAG:Ce phosphors were measured. In this experiment, regarding the
chromaticity, the value x of the chromaticity coordinates in the
XYZ colorimetric system of the International Commission on
Illumination (CIE) was measured.
FIG. 3 is a graph illustrating the relationship between the Ga
concentration and the luminescent chromaticity (value x) and the
relationship between the Ga concentration and the absorptance for
blue-violet light, with regard to the YAG:Ce phosphors. Note that
the "Ga concentration" refers to the ratio (%) of the number of
moles of Ga to the total number of moles of Al and Ga.
Consequently, for example, when the Ga concentration is 30%, the
addition amount (b) of Ga in the general formula is 1.5.
As is evident from FIG. 3, as the Ga concentration increases, the
absorptance for excitation light increases, but the luminescent
chromaticity (value x) decreases. That is, there is a trade-off
relation between the absorptance and the chromaticity. When the
chromaticity decreases, it may not be possible to obtain good
yellow light emission in some cases.
Accordingly, the present inventors conducted further studies on the
composition of a compound that can enhance the external quantum
efficiency while securing the desired luminescent chromaticity and
studies on the process therefor. As a result, it was found that,
when the addition amount of Ce in a YAG:Ce phosphor is increased,
it is possible to enhance the luminescent chromaticity.
The present inventors conducted studies on the relationship between
the Ce concentration and the internal quantum efficiency and the
relationship between the Ce concentration and the luminescent
chromaticity, with regard to YAG:Ce phosphors in Experiment 2. The
procedure and results thereof will be described below.
In Experiment 2, a plurality of YAG:Ce phosphors represented by the
general formula
(3-a)YO.sub.3/2.aCeO.sub.3/2.(5-b)AlO.sub.3/2.bGaO.sub.3/2 were
produced by setting the addition amount (b) of Ga in the general
formula to be 1.25 and the addition amount (a) of Ce in the general
formula to be varied. The YAG:Ce phosphors were produced by firing
mixtures prepared by mixing starting materials at predetermined
ratios. The firing was performed under the same conditions as those
in Experiment 1. Subsequently, the internal quantum efficiency and
luminescent chromaticity of the resulting YAG:Ce phosphors were
measured.
FIG. 4 is a graph illustrating the relationship between the Ce
concentration and the luminescent chromaticity and the relationship
between the Ce concentration and the internal quantum efficiency,
with regard to YAG:Ce phosphors. The "Ce concentration" refers to
the ratio (%) of the number of moles of Ce to the total number of
moles of Y and Ce. Consequently, for example, when the Ce
concentration is 4%, the addition amount (a) of Ce in the general
formula is 0.12.
As is evident from FIG. 4, as the Ce concentration increases, the
luminescent chromaticity of phosphors increases. This result shows
that, in YAG:Ce phosphors to which Ga is added, by increasing the
Ce concentration, it is possible to obtain yellow light emission.
However, as the Ce concentration increases, the internal quantum
efficiency decreases. That is, there is a trade-off relation
between the luminescent chromaticity and the internal quantum
efficiency. Therefore, although the absorptance can be increased by
adding Ga, it is difficult to improve the external quantum
efficiency, which is the product of the absorptance and the
internal quantum efficiency.
Under the circumstances, the present inventors conducted further
studies and found that when potassium (K) and phosphorus (P) are
further added to a YAG:Ce phosphor having a high Ce concentration,
it is possible to suppress a decrease in the internal quantum
efficiency, thus devising a phosphor according to the present
disclosure. According to one aspect of the present disclosure, it
is possible to provide a yellow light-emitting phosphor which can
have high external quantum efficiency for blue-violet excitation
light.
Aspects of the present disclosure are based on the above-described
knowledge and can be summarized below.
A phosphor according to one aspect of the present disclosure
includes, as a main component, a compound represented by the
general formula
(3-a)YO.sub.3/2.aCeO.sub.3/2.(5-b)AlO.sub.3/2.bGaO.sub.3/2.cKO.sub.1/2.dP-
O.sub.5/2. In the general formula, a, b, c and d satisfy
0.12.ltoreq.a.ltoreq.0.18, 1.50 b.ltoreq.3.00,
0.01.ltoreq.c.ltoreq.0.08, and 0.01.ltoreq.d.ltoreq.0.08.
A light-emitting device according to another aspect of the present
disclosure includes the phosphor and an excitation light source
which emits first light having a peak wavelength of 380 to 420 nm.
The phosphor absorbs part of the first light from the excitation
light source and thereby emits second light having a longer
wavelength than the first light.
A method for producing a phosphor according to another aspect of
the present disclosure is a method for producing a phosphor. The
phosphor includes, as a main component, a compound represented by
the general formula
(3-a)YO.sub.3/2.aCeO.sub.3/2.(5-b)AlO.sub.3/2.bGaO.sub.3/2.cKO.su-
b.1/2.dPO.sub.5/2 (0.12.ltoreq.a.ltoreq.0.18,
1.50.ltoreq.b.ltoreq.3.00, 0.01.ltoreq.c.ltoreq.0.08,
0.01.ltoreq.d.ltoreq.0.08). This method includes (i) preparing a
mixture which includes starting materials for the phosphor and (ii)
firing the mixture. The firing of the mixture is performed in an
atmosphere with an oxygen partial pressure of 10.sup.-6 to
10.sup.-3 atm.
The mixture may include, as a reaction accelerator, a
fluorine-containing compound.
(First Embodiment)
A phosphor according to a first embodiment will be described
below.
A phosphor according to this embodiment includes, as a main
component, a compound represented by the general formula
(3-a)YO.sub.3/2.aCeO.sub.3/2.(5-b)AlO.sub.3/2.bGaO.sub.3/2.cKO.sub.1/2.dP-
O.sub.5/2. In the general formula, a, b, c and d satisfy
0.12.ltoreq.a.ltoreq.0.18, 1.50 b.ltoreq.3.00,
0.01.ltoreq.c.ltoreq.0.08, 0.01.ltoreq.d.ltoreq.0.08. In this
specification, a, b, c, and d in the general formula refer to the
addition amounts of Ce, Ga, K, and P, respectively.
Note that the phrase "includes, as a main component" means that,
for example, the compound is included in an amount of 70% by weight
or more, or desirably 90% by weight or more, relative to the entire
phosphor. The phosphor according to this embodiment may include, in
addition to the compound represented by the general formula, an
additive, an impurity, or the like.
When the addition amount (b) of Ga in the general formula is 1.50
or more, it is possible to enhance the absorptance for blue-violet
light. On the other hand, when the addition amount (b) of Ga in the
general formula is 3.00 or less, it is possible to suppress a
decrease in luminescent chromaticity. When the addition amount (a)
of Ce in the general formula is 0.12 or more, it is possible to
suppress a decrease in luminescent chromaticity due to addition of
Ga, and yellow light emission can be realized. When the addition
amount (a) of Ce in the general formula is 0.18 or less, it is
possible to suppress a decrease in internal quantum efficiency due
to segregation of Ce and the like. Furthermore, when the addition
amount (c) of K and the addition amount (d) of P are each in a
range of 0.01 to 0.08, the Ce concentration distribution can be
made more uniform, and therefore, internal quantum efficiency can
be enhanced.
Accordingly, the phosphor according to this embodiment can be used
as a yellow phosphor which has high external quantum efficiency for
blue-violet excitation light.
<Method of Producing Phosphor>
An example of a method of producing the phosphor according to this
embodiment will be described below. Note that as long as the
phosphor according to this embodiment includes, as a main
component, the compound represented by the formula described above,
the production method therefor is not limited to that described
below.
As starting materials for the phosphor, compounds which are
convertible to oxides by firing, such as high purity (purity 99% or
more) hydroxides, carbonates, and nitrates, or high purity (purity
99% or more) oxides can be used. In order to accelerate the
reaction, a fluorine (F)-containing compound (e.g., a fluoride,
such as aluminum fluoride) may be added. The amount of the fluoride
added is not particularly limited. The amount of the fluoride may
be, for example, 0.1 to 10 mole percent (e.g., 1 mole percent)
relative to the phosphor.
The starting materials are mixed to obtain a mixed powder. As a
method for mixing starting materials, wet mixing in a solution or
dry mixing of dry powders may be used. In the mixing method, a ball
mill, a medium agitation mill, a planetary mill, a vibration mill,
a jet mill, a V-type mixer, an agitator, or the like, which is
normally used industrially, can be used.
Subsequently, by firing the mixed powder, a phosphor according to
this embodiment is obtained.
The firing of the mixed powder is performed in an atmosphere
containing oxygen. The oxygen partial pressure (hereinafter,
referred to as the "oxygen partial pressure in the firing
atmosphere") at the firing temperature is, for example, set to be
10.sup.-6 to 10.sup.-3 atm. A mixed gas containing carbon dioxide
gas may be used as the atmospheric gas. In the case where a mixed
gas containing nitrogen gas, hydrogen gas, and carbon dioxide gas
is used, the content of hydrogen gas may be more than 0% and less
than or equal to 5% by volume and the content of carbon dioxide gas
may be more than 0% and less than or equal to 50% by volume
relative to the entire mixed gas. The oxygen partial pressure can
be adjusted by the mixing ratio in the mixed gas. The firing
temperature may be set, for example, to be in a range of
1,500.degree. C. to 1,700.degree. C. The firing time may be, for
example, in a range of 1 to 50 hours.
A furnace which is normally used industrially can be used in the
firing. For example, a continuous electric furnace such as a pusher
furnace, or a batch-type electric furnace or gas furnace may be
used.
The phosphor powder which has been fired may be pulverized again by
using a ball mill, a jet mill, or the like, and furthermore, may be
optionally washed or classified. Thereby, it is possible to adjust
the particle size distribution and fluidity of the phosphor
powder.
In the method described above, the oxygen partial pressure in the
firing atmosphere is set to be higher than that in existing
methods. Thereby, it is possible to suppress a decrease in internal
quantum efficiency due to addition of Ce. The reason for this will
be described below.
In existing methods of producing a YAG:Ce phosphor, when a mixed
powder is fired in a chamber, a mixed gas containing nitrogen gas
and hydrogen gas is used as an atmospheric gas, or firing is
performed in a vacuum. Accordingly, the atmosphere in the chamber
does not substantially contain oxygen, and the oxygen partial
pressure in the chamber is 10.sup.-10 atm or less.
The present inventors conducted studies and found that when a
phosphor including Ce and Ga at relatively high concentrations is
produced by the same method as the existing methods, there is a
possibility that a phosphor having high internal quantum efficiency
will not be obtained. It is believed that factors for this include
the occurrence of crystal defects due to an oxygen deficiency
caused by the firing and segregation of part of Ce without being
replaced, a degradation in crystallinity due to sublimation of Ga
from the mixed powder during the firing, and the like.
For example, in Experiment 2 described above, phosphors including
Ce and Ga at relatively high concentrations were fired in nitrogen
gas which contained hydrogen gas (hydrogen gas content: 2%). The
oxygen partial pressure at the firing temperature was about
10.sup.-12 atm. As a result, as shown in FIG. 4, as the Ce
concentration increases, the internal quantum efficiency decreases
markedly. The reason for this is believed to be that when the Ce
concentration increases (e.g., to more than 3%), Ce is not
effectively replaced, resulting in an increase in crystal
defects.
In contrast, in the firing process according to this embodiment, by
using oxygen-containing gas (e.g., carbon dioxide gas) as the
atmospheric gas, the oxygen partial pressure in the atmosphere is
increased, for example, to 10.sup.-6 atm or more. Thereby, the
sublimation of Ga can be suppressed, and the oxygen deficiency can
be decreased. Furthermore, by increasing the oxygen partial
pressure and adding P and K, even when the Ce concentration
increases, Ce and Y can be effectively replaced. Therefore, it is
possible to more effectively suppress a degradation in
crystallinity and a decrease in internal quantum efficiency due to
crystal defects and the like.
(Study on Oxygen Partial Pressure)
Regarding two phosphors A and B having different compositions, the
relationship between the oxygen partial pressure in the firing
atmosphere and the internal quantum efficiency of the phosphors was
checked The procedure and results thereof will be described
below.
The compositions of the phosphor A and the phosphor B are as
follows:
Phosphor A:
(3-a)YO.sub.3/2.aCeO.sub.3/2.(5-b)AlO.sub.3/2.bGaO.sub.3/2.cKO.sub.1/2.dP-
O.sub.5/2, where a=0.12, b=2.25, and c=d=0.01.
Phosphor B:
(3-a)YO.sub.3/2.aCeO.sub.3/2.(5-b)AlO.sub.3/2.bGaO.sub.3/2.cKO.sub.1/2.dP-
O.sub.5/2, where a=0.06, and b=c=d=0.
The phosphor A is a phosphor of Example which includes Ce, Ga, K,
and P. The phosphor B is a phosphor of Comparative Example in which
the addition amount (a) of Ce in the general formula is small and
which does not include any of Ga, K, and P.
First, mixed powders serving as starting materials for the
phosphors A and B were prepared. A plurality of samples were
obtained by firing the mixed powders, at different oxygen partial
pressures in the atmosphere, at a temperature of 1,650.degree. C.
for 16 hours. In the firing process, a mixed gas containing
nitrogen gas, hydrogen gas, and carbon dioxide gas was used as the
atmospheric gas, and the mixing ratio of the gases was adjusted to
obtain predetermined oxygen partial pressures. Subsequently, the
internal quantum efficiency of the resulting samples of the
phosphors A and B was measured.
FIG. 5 is a graph showing an example of the relationship between
the oxygen partial pressure in the firing atmosphere and the
internal quantum efficiency of phosphors.
As shown in FIG. 5, in the phosphor B, high internal quantum
efficiency can be obtained in a wide range of oxygen partial
pressure (e.g., 10.sup.-2 atm or less).
On the other hand, in the phosphor A, the internal quantum
efficiency varies depending on the oxygen partial pressure in the
firing atmosphere. When the oxygen partial pressure is 10.sup.-6 to
10.sup.-3 atm, higher internal quantum efficiency can be obtained.
In particular, as is evident from the graph, by adjusting the
oxygen partial pressure in a specific range (in this example,
10.sup.-6 to 10.sup.-4 atm), it is possible to achieve higher
internal quantum efficiency than that of the phosphor B in which
the addition amount of Ce is small. The reason for this is believed
to be that by adding K and P to the phosphor and setting the oxygen
partial pressure in the firing atmosphere to be 10.sup.-6 atm or
more, Ce can be effectively replaced by firing. On the other hand,
it is believed that when the oxygen partial pressure is either
higher or lower than the range described above, Ce cannot be
effectively replaced, resulting in an increase in crystal defects,
and therefore, the internal quantum efficiency is decreased.
Note that the desirable range of oxygen partial pressure in the
firing atmosphere is not limited to the example shown in FIG. 5.
The range may vary depending on the composition of the phosphor (in
particular, the addition amount (a) of Ce and the addition amount
(b) of Ga in the general formula) and firing conditions, such as
the firing temperature. It is believed that when the oxygen partial
pressure is at least in the range of 10.sup.-6 to 10.sup.-3 atm,
higher internal quantum efficiency can be obtained.
(Light-Emitting Device)
The phosphor according to this embodiment has high external quantum
efficiency, and therefore can constitute a highly efficient
light-emitting device.
A light-emitting device according to this embodiment includes an
excitation light source which emits first light and the phosphor.
The phosphor absorbs part of the first light from the excitation
light source and emits second light having a longer wavelength than
the first light. The first light is, for example, blue-violet light
having a peak wavelength in a range of 380 to 420 nm. The second
light is, for example, yellow light having a peak wavelength in a
range of 530 to 550 nm.
The excitation light source may be a semiconductor light-emitting
element, such as a blue-violet LD or blue-violet LED. The structure
of the light-emitting device other than the phosphor may be the
same as that of an existing light-emitting device including a
YAG:Ce phosphor.
Examples of the light-emitting device include an illumination light
source including a blue-violet LD or blue-violet LED and the
phosphor.
EXAMPLES
Phosphor samples of Example and Comparative Example were produced
and evaluated, which will be described below.
<Production of Phosphor Samples>
Y.sub.2O.sub.3, Al.sub.2O.sub.3, Ga.sub.2O.sub.3, CeCl.sub.3,
K.sub.2CO.sub.3, and NH.sub.4H.sub.2PO.sub.4 were used as starting
materials, and AlF.sub.3 was used as a reaction accelerator.
First, the starting materials were weighed so that predetermined
compositions would be obtained, and wet mixing was performed in
pure water by using a ball mill.
The resulting mixtures were dried, and then fired to obtain
phosphors. In the firing process, a mixed gas containing hydrogen
gas, carbon dioxide gas, and nitrogen gas was used as the
atmospheric gas. The mixing ratio in the mixing gas was adjusted
such that the content of hydrogen gas was more than 0% and less
than or equal to 5% by volume and the content of carbon dioxide gas
was more than 0% and less than or equal to 50% by volume relative
to the entire mixed gas, and such that the oxygen partial pressure
at the firing temperature was close to 10.sup.-4 atm. The firing
temperature was set to be in a range of 1,500.degree. C. to
1,700.degree. C., and the firing time was set to be 16 hours.
Subsequently, the resulting phosphor powders were pulverized again
by using a ball mill to adjust the particle size distribution. In
such a manner, phosphor samples 1 to 22 were obtained. Regarding
the phosphor samples, the addition amounts (a), (b), (c), and (d)
of Ce, Ga, K, and P in the general formula
(3-a)YO.sub.3/2.aCeO.sub.3/2.(5-b)AlO.sub.3/2.bGaO.sub.3/2.cKO.sub.1/2.dP-
O.sub.5/2 are shown in Table.
<Measurement of External Quantum Efficiency and
Chromaticity>
The phosphor samples 1 to 22 were irradiated with blue-violet light
with a wavelength of 405 nm serving as excitation light. The
internal quantum efficiency of luminescence in the yellow range,
the excitation light absorptance, and the luminescent chromaticity
(value x of CIE chromaticity coordinates) in each phosphor sample
were measured. The measurement was performed by using an absolute
PL quantum yield spectrometer (manufactured by Hamamatsu Photonics,
C9920). Furthermore, the external quantum efficiency was calculated
from the internal quantum efficiency and the excitation light
absorptance. The external quantum efficiency and the luminescent
chromaticity of each phosphor sample are shown in Table.
Among all the phosphor samples, phosphor samples 9 to 22 correspond
to Example having the composition ratio described in the first
embodiment, and the others correspond to Comparative Example.
TABLE-US-00001 TABLE External Addition Addition Addition addition
quantum Luminescent amount (a) amount (b) amount (c) amount (d)
efficiency chromaticity of Ce of Ga of K of P (%) (value x)
Comparative 1 0.06 1.50 0.01 0.01 45 0.32 Example 2 0.36 1.50 0.01
0.01 32 0.39 3 0.15 0 0.01 0.01 15 0.43 4 0.15 4.50 0.01 0.01 52
0.30 5 0.15 1.50 0 0.01 46 0.38 6 0.15 1.50 0.20 0.01 54 0.39 7
0.15 1.50 0.01 0 58 0.37 8 0.15 1.50 0.01 0.20 42 0.35 Example 9
0.12 1.50 0.01 0.01 62 0.40 10 0.15 1.50 0.01 0.01 64 0.42 11 0.18
1.50 0.01 0.01 63 0.44 12 0.18 3.00 0.08 0.08 65 0.41 13 0.12 1.50
0.02 0.02 71 0.42 14 0.12 2.00 0.02 0.02 73 0.40 15 0.12 2.00 0.04
0.01 75 0.41 16 0.15 1.50 0.02 0.02 68 0.43 17 0.15 2.00 0.02 0.02
72 0.41 18 0.15 2.50 0.02 0.02 70 0.40 19 0.15 2.00 0.04 0.01 76
0.43 20 0.15 2.00 0.04 0.02 75 0.42 21 0.15 2.00 0.06 0.02 71 0.42
22 0.18 2.00 0.06 0.02 65 0.43
As is evident from the results shown in Table, in phosphor samples
9 to 22 in which the conditions 0.12.ltoreq.a.ltoreq.0.18, 1.50
b.ltoreq.3.00, 0.01.ltoreq.c.ltoreq.0.08, and
0.01.ltoreq.d.ltoreq.0.08 are satisfied, when blue-violet light is
used as excitation light, the external quantum efficiency is high,
and the chromaticity (value x: 0.40 or more) that is desirable as
yellow light emission can be obtained.
FIG. 1 is a graph showing the relationship between the addition
amount (a) of Ce in the general formula and the external quantum
efficiency and the relationship between the addition amount (a) of
Ce in the general formula and the chromaticity, with regard to
phosphor samples 1 and 2 of Comparative Example and phosphor
samples 9 to 11 of Example. As is evident from FIG. 1, when the
addition amount of Ce is in a range of 0.12 to 0.18, it is possible
to achieve both desired luminescent chromaticity and high external
quantum efficiency.
FIG. 2 is a graph showing the relationship between the addition
amount (b) of Ga in the general formula and the external quantum
efficiency and the relationship between the addition amount (b) of
Ga in the general formula and the chromaticity, with regard to
phosphor samples 3 and 4 of Comparative Example and phosphor
samples 10 and 16 to 21 of Example. As is evident from FIG. 2, when
the addition amount of Ga is in a range of 1.50 to 3.00, it is
possible to enhance external quantum efficiency while suppressing a
decrease in luminescent chromaticity.
The phosphor according to the embodiment of the present disclosure
can be used in various light-emitting devices. For example, the
phosphor can be used in illumination light sources and projectors
using light-emitting diodes (LEDs) or laser diodes (LDs) and
phosphors. Furthermore, the phosphor can be used in liquid crystal
displays provided with an LED backlight, and sensors and
sensitizers using phosphors.
* * * * *