U.S. patent application number 17/033682 was filed with the patent office on 2021-04-08 for red phosphor and light emitting device using the same.
The applicant listed for this patent is Panasonic Intellectual Property Management Co., Ltd.. Invention is credited to SHINNOSUKE AKIYAMA, RIHO MORIYAMA, KEI TOYOTA.
Application Number | 20210102118 17/033682 |
Document ID | / |
Family ID | 1000005153422 |
Filed Date | 2021-04-08 |
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United States Patent
Application |
20210102118 |
Kind Code |
A1 |
MORIYAMA; RIHO ; et
al. |
April 8, 2021 |
RED PHOSPHOR AND LIGHT EMITTING DEVICE USING THE SAME
Abstract
A red phosphor is expressed by a chemical formula of
Ca.sub.zO:Ce.sub.x, Li.sub.y, in which a range of x values is
0<x<0.2, a range of y values is 0.ltoreq.y<0.2, and a
range of z values is 1-x-y.ltoreq.z.ltoreq.1-x.
Inventors: |
MORIYAMA; RIHO; (Osaka,
JP) ; AKIYAMA; SHINNOSUKE; (Okayama, JP) ;
TOYOTA; KEI; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Panasonic Intellectual Property Management Co., Ltd. |
Osaka |
|
JP |
|
|
Family ID: |
1000005153422 |
Appl. No.: |
17/033682 |
Filed: |
September 26, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 33/0004 20130101;
C09K 11/7718 20130101; H01L 33/504 20130101; H01L 2933/0041
20130101; F21V 9/30 20180201 |
International
Class: |
C09K 11/77 20060101
C09K011/77; H01L 33/50 20060101 H01L033/50; H01L 33/00 20060101
H01L033/00; F21V 9/30 20060101 F21V009/30 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 3, 2019 |
JP |
2019-183018 |
Claims
1. A red phosphor of a chemical formula Ca.sub.zO:Ce.sub.x,
Li.sub.y, wherein a range of values of x is 0<x<0.2, a range
of values of y is 0.ltoreq.y<0.2, and a range of values of z is
1-x-y.ltoreq.z.ltoreq.1-x.
2. A light emitting device comprising: the red phosphor of claim 1;
and a light source having a light emission peak wavelength in a
range of 400 nm to 500 nm, inclusive.
Description
BACKGROUND
1. Technical Field
[0001] The present disclosure relates to a red phosphor that
absorbs blue-based excitation light and emits red fluorescence, and
a light emitting device using the red phosphor.
2. Description of the Related Art
[0002] A semiconductor light emitting element such as a light
emitting diode (LED) has advantages that it is small in size,
consumes less power, and can stably emit light with high
brightness, and in recent years, there has been a movement to
replace a lighting fixture such as an incandescent lamp with a
lighting fixture that uses a light emitting device including an LED
that emits white light. As an LED that emits white light, there is,
for example, an LED in which a blue LED is combined with a
Ce-activated YAG-based yellow phosphor expressed by a composition
formula of Y.sub.3Al.sub.5O.sub.12:Ce.
[0003] In the light emitting device having the configuration
described above, white light is realized by mixing blue light of
the LED and yellow light emitted from the Ce-activated YAG
phosphor. In this configuration, the white light is pale white
light due to light emission characteristics of the Ce-activated YAG
phosphor. On the other hand, there is a strong demand for slightly
reddish warm-colored white light for display lighting in stores, in
medical field lighting and the like, and the light emitting device
having the configuration described above is not suitable for
emitting warm white light.
[0004] A light emitting device capable of emitting a reddish
warm-colored white color by further combining an Eu-activated
nitride-based red phosphor expressed by the composition formula of
Ca.sub.2Si.sub.5N.sub.7:Eu, in addition to the blue LED and the
Ce-activated YAG-based phosphor, is disclosed (for example, see
Japanese Patent Unexamined Publication No. 2003-321675).
[0005] It is disclosed that the configuration described in Japanese
Patent Unexamined Publication No. 2003-321675 enables a light
emitting device that emits white light that exhibits a high color
rendering index (Ra), and particularly an excellent special color
rendering index (R9) showing the appearance of red, at a color
temperature of a light bulb color region of 3,250 K or less.
SUMMARY
[0006] According to one aspect of the present disclosure, there is
provided a red phosphor of a chemical formula Ca.sub.zO:Ce.sub.x,
Li.sub.y, in which a range of values of x is 0<x<0.2, a range
of values of y is 0.ltoreq.y<0.2, and a range of values of z is
1-x-y.ltoreq.z.ltoreq.1-x.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a schematic diagram of a crystal structure of a
mother crystal of a red phosphor according to Embodiment 1;
[0008] FIG. 2 is a light emission spectrum of a red phosphor of
Example 1 according to Embodiment 1;
[0009] FIG. 3 is a schematic cross-sectional view of an LED light
emitting device according to Embodiment 2;
[0010] FIG. 4 is a schematic cross-sectional view of an LD light
emitting device according to Embodiment 3;
[0011] FIG. 5 is Table 1 showing values of x, y, z, formulation
amounts of raw materials, evaluation results, and the like in red
phosphors that can be expressed by Ca.sub.zO:Ce.sub.x, Li.sub.y of
Examples 1 to 3;
[0012] FIG. 6 is Table 2 showing values of x, y, z, formulation
amounts of raw materials, evaluation results, and the like in red
phosphors that can be expressed by Ca.sub.zO:Ce.sub.x, Li.sub.y of
Example 4 and Comparative Examples 1 and 2;
[0013] FIG. 7 is Table 3 showing values of x, y, z, formulation
amounts of raw materials, evaluation results, and the like in red
phosphors that can be expressed by Ca.sub.zO:Ce.sub.x, Li.sub.y of
Example 1, Example 5, and Comparative Example 3; and
[0014] FIG. 8 is Table 4 showing 1/e light emission lifetimes of
Examples 1, 2, and 5 and Comparative Example 4.
DETAILED DESCRIPTIONS
[0015] In the red phosphor described in Japanese Patent Unexamined
Publication No. 2003-321675, Eu having a long light emission
lifetime is activated as a light emission center. For that reason,
for example, when a high-power excitation light source such as a
blue laser is applied as an excitation light source to realize a
high-brightness, high-color-rendering light source, light emission
brightness decreases due to brightness saturation under a
high-power light source, and thus the brightness required for the
device cannot be secured. In the future, it is considered that a
red phosphor having light emission brightness compatible with a
high-power light source will be required due to market needs such
as higher brightness and higher color rendering property of a light
source and a projector.
[0016] The present disclosure solves the related art problems
described above, and an object thereof is to provide a red phosphor
with little decrease in light emission brightness due to brightness
saturation under a high-power light source.
[0017] According to a first aspect of the present disclosure, there
is provided a red phosphor expressed by a chemical formula of
Ca.sub.zO:Ce.sub.x, Li.sub.y, in which a range of values of x is
0<x<0.2, a range of values of y is 0.ltoreq.y<0.2, and a
range of values of z is 1-x-y.ltoreq.z.ltoreq.1-x.
[0018] According to a second aspect of the present disclosure,
there is provided a light emitting device including the red
phosphor according to the first aspect and a light source having a
light emission peak wavelength in a range of 400 nm to 500 nm,
inclusive.
[0019] As described above, since the red phosphor according to the
present disclosure has a configuration expressed by the chemical
formula described above, the red phosphor has a light emission peak
wavelength of 560 nm or more and 700 nm or less and exhibits a high
color rendering property in a long wavelength region within a
visible light region, and has a little decrease in light emission
brightness under irradiation with a high-power light source.
Accordingly, for example, a light emitting device having high
brightness and high color rendering can be obtained by combining a
light source emitting blue light and having a light emission peak
wavelength of 450 nm with the red phosphor according to the present
disclosure.
[0020] Hereinafter, a red phosphor according to an exemplary
embodiment will be described with reference to the accompanying
drawings. In the drawings, substantially the same members are
designated by the same reference numerals.
Embodiment 1
Red Phosphor
[0021] The red phosphor according to Embodiment 1 is expressed by
the chemical formula of Ca.sub.zO:Ce.sub.x, Li.sub.y, in which a
range of values of x is 0<x<0.2, a range of values of y is
0.ltoreq.y<0.2, and a range of values of z is
1-x-y.ltoreq.z.ltoreq.1-x. In general, optical characteristics of
phosphor are determined by a type of mother crystal and light
emission center. For example, Y.sub.3Al.sub.5O.sub.12:Ce, which is
generally known as a yellow phosphor, has a mother crystal of
Y.sub.3Al.sub.5O.sub.12 crystal having a garnet structure, and a
light emission center thereof is Ce. FIG. 1 illustrates a schematic
diagram of a crystal structure of a mother crystal of the red
phosphor according to Embodiment 1. The mother crystal of the red
phosphor according to Embodiment 1 is CaO crystal 1 having a rock
salt type structure, and the light emission center of the red
phosphor is Ce. In CaO crystal 1, a site containing Ca is called Ca
site 2, a site containing O is called O site 3, and a space between
Ca site 2 and O site 3 is called interstitial 4. Three types of
structures can be considered for the red phosphor according to
Embodiment 1. The first type is the case where all Ce are replaced
by Ca sites 2 and all Li are replaced by Ca sites 2, that is, a
value of z is z=1-x-y. The second type is the case where all Ce is
replaced by Ca sites 2 and all Li exists in interstitial 4, that
is, z=1-x. The third type is the case where all Ce are replaced by
Ca sites 2, some Li are replaced by Ca sites 2, and all the
remaining Li exists in interstitial 4, that is, the value of z is
1-x-y<z<1-x.
[0022] In the chemical formula described above, the value of x is
larger than 0 because Ce, which serves as the light emission
center, needs to be included in order to obtain light emission. The
value of x is preferably 0.0001 or more, and more preferably 0.003
or more from the viewpoint of increasing light emission intensity.
There is no particular limitation on the maximum value of x as long
as the red phosphor can emit light. However, when the value of x
becomes too large, the light emission intensity will decrease due
to concentration quenching. For that reason, a decrease in light
emission intensity can be controlled by setting the value of x to
be less than 0.2. The value of x is preferably 0.1 or less, more
preferably 0.03 or less from the viewpoint of increasing the light
emission intensity.
[0023] In order to obtain light emission, it is not always
necessary to contain Li, but it is desirable to contain Li from the
viewpoint of obtaining light emission on the longer wavelength
side. There is no particular limitation on the maximum value of y
as long as the red phosphor can emit light. However, when the value
of y becomes too large, Li interferes with light emission of Ce and
the light emission intensity is decreased. For that reason, it is
possible to control the decrease in light emission intensity by
setting the value of y to be less than 0.2.
[0024] In a case where the value of z is smaller than 1-x-y, that
is, the amount of Ca is less than the total amount of Ce and Li,
when synthesized with such a formulation, Ce and Li are deposited
as impurities in order to match the amount of Ca, and eventually
the value of z becomes 1-x-y or more and a stable crystal structure
is obtained. In a case where the value of z is larger than 1-x,
that is, the amount of Ca is greater than the amount of Ce, when
synthesized with such a formulation, since there is no space for Ce
to enter the Ca site 2, Ce is deposited as an impurity, and
eventually the value of z becomes 1x and a stable crystal structure
is obtained. From the viewpoints described above, the value of z is
in the range of 1-x-y z 1-x.
[0025] Here, the light emission peak is a peak having the maximum
value in the entire spectrum. The light emission peak appears when
excited at a wavelength of 450 nm.
[0026] The 1/e light emission lifetime of the red phosphor
according to Embodiment 1 may exhibit a value of 100 ns or less.
The light emission lifetime affects brightness saturation
characteristics. The red phosphor containing Eu, such as CASN:Eu,
which is a red phosphor of the related art, has a larger light
emission lifetime value, that is, a longer light emission lifetime
than a red phosphor containing Ce. For that reason, the red
phosphor containing Eu is likely to be saturated in brightness due
to a decrease in quantum efficiency during high-power excitation.
Accordingly, the red phosphor according to Embodiment 1 in which Ce
is activated as a light emission center is promising as a red
phosphor having high quantum efficiency even at high power, as
compared with the red phosphor of the related art.
Method for Manufacturing Red Phosphor
[0027] Hereinafter, a method for manufacturing the red phosphor
according to Embodiment 1 will be described.
[0028] (1) As the raw material, for example, an oxide of cerium
(Ce), lithium (Li), and calcium (Ca), which are elements
constituting a mother crystal and an activator, can be used. Cerium
oxide, calcium oxide, and lithium oxide are prepared as raw
material oxides. The raw materials may be metal salt compounds such
as carbonates instead of these oxides.
[0029] (2) Predetermined amounts of these powders are measured and
mixed well. The mixing method may be wet mixing in a solution or
dry mixing of dry powder. For the mixing, an industrially used ball
mill, medium stirring mill, planetary mill, vibration mill, jet
mill, stirrer or the like can be used. It is also possible to carry
out the mixing manually using a mortar or the like. Barium fluoride
(BaF.sub.2) or strontium fluoride (SrF.sub.2) may be mixed as a
flux in an amount corresponding to 0.1 to 10 wt % of the mixed
powder.
[0030] (3) Next, the mixed powder prepared as described above is
baked. For the baking, for example, an electric furnace can be
used. For example, the mixed powder is put into an alumina crucible
and heated together with the alumina crucible at 1200.degree. C. or
higher and 1600.degree. C. or lower for a time of about 3 hours to
12 hours and baked.
[0031] (4) After baking, the red phosphor powder can be obtained by
cooling, crushing, and if necessary, through steps such as flux
washing with an acid.
Embodiment 2
Light Emitting Device
[0032] In Embodiment 2, as an example of the light emitting device
of the present disclosure, an LED light emitting device including
the red phosphor according to Embodiment 1 and an LED chip as a
light source will be described. FIG. 3 is a schematic
cross-sectional view illustrating an embodiment of the LED light
emitting device according to Embodiment 2. As illustrated in FIG.
3, LED light emitting device 10 includes LED wavelength conversion
member 11 and LED chip 13. LED light emitting device 10 may include
support 17. Support 17 supports LED chip 13. In this embodiment,
since LED light emitting device 10 has a structure capable of
surface mounting, support 17 is a board. LED wavelength conversion
member 11 includes at least red phosphor 21 and LED sealant 12.
[0033] The LED light emitting device according to Embodiment 2 can
be used for a high-brightness LED light emitting device.
[0034] The members constituting the LED light emitting device will
be described below.
Support
[0035] Support 17 has a high thermal conductivity so that heat
generated in LED chip 13 can be efficiently radiated to the
outside, for example. For support 17, for example, a ceramic board
made of alumina, aluminum nitride, or the like can be used.
LED Chip
[0036] As LED chip 13, for example, one that emits light in a
region extending from the lower end of the ultraviolet region to
yellow region, that is, one that has a peak of the light emission
spectrum in the wavelength region of 400 nm to 500 nm is used. As
LED chip 13, specifically, a blue LED chip or the like is used. LED
chip 13 is fixed to support 17 by solder 15 or the like so that an
emission surface does not come into contact with support 17 on
support 17. LED chip 13 is electrically connected to electrode 16
provided on support 17 by bonding wire 14. LED chip 13 is covered
with LED sealant 12.
LED Wavelength Conversion Member
[0037] LED wavelength conversion member 11 is configured by using
LED sealant 12. Silicone resin is used for LED sealant 12. The
silicone resin contains, for example, dimethyl silicone, which has
high discoloration resistance. Methylphenyl silicone or the like
having high heat resistance can also be used as the silicone resin.
The silicone resin may be a homopolymer having a main skeleton with
a siloxane bond defined by one type of chemical formula. The
silicone resin may be a copolymer containing a structural unit
having a siloxane bond defined by two or more types of chemical
formulas, or an alloy of two or more types of silicone
polymers.
[0038] LED wavelength conversion member 11 includes a phosphor. The
phosphor converts light emitted from LED chip 13 into light having
a longer wavelength. The phosphor contained in LED wavelength
conversion member 11 is configured by mixing red phosphor 21 and at
least one of yellow phosphor 22 and green phosphor 23. As red
phosphor 21, the red phosphor according to Embodiment 1 is used. As
yellow phosphor 22, for example, Y.sub.3Al.sub.5O.sub.12:Ce,
.alpha.-SiAlON:Eu, or the like can be used. As green phosphor 23,
Ca.sub.3SiO.sub.4Cl.sub.2:Eu, .beta.-SiAlON:Eu, or the like can be
used. In this embodiment, in particular, a case where LED
wavelength conversion member 11 is configured by mixing three types
of red phosphor 21, yellow phosphor 22, and green phosphor 23 will
be described. A mixing ratio of the three types of phosphors can be
appropriately adjusted according to a desired color tone of white
light, light emission intensity of each phosphor, and the like. The
three types of phosphors of red phosphor 21, yellow phosphor 22,
and green phosphor 23 are contained in LED sealant 12 at a ratio of
3 parts by weight or more and 70 parts by weight or less with
respect to 100 parts by weight of the sealant, for example. When
the content is less than 3 parts by weight, sufficient intensity of
fluorescence cannot be obtained, and thus LED light emitting device
10 that emits light of a desired wavelength may not be realized. A
weight ratio of the three types of phosphors can be appropriately
determined depending on the desired color tone of white light and
light emission intensity of each phosphor.
[0039] LED light emitting device 10 can be configured as LED light
emitting device 10 that emits a color other than white by combining
red phosphor 21 and the phosphors of other colors.
[0040] Yellow phosphor 22 and green phosphor 23 other than red
phosphor 21 according to Embodiment 1 can be manufactured according
to known methods.
Embodiment 3
Light Emitting Device
[0041] In Embodiment 3, as an example of the light emitting device
of the present disclosure, an LD light emitting device including
the red phosphor according to Embodiment 1 and an LD element as a
light source will be described. FIG. 4 illustrates a schematic
configuration of LD light emitting device 20 according to
Embodiment 3. LD light emitting device 20 includes LD element 27
and LD wavelength conversion member 25. LD wavelength conversion
member 25 includes at least red phosphor 21 and binder 24.
[0042] The members constituting this LD light emitting device will
be described below.
LD Element
[0043] LD element 27 can emit light having an optical power density
higher than that of the LED. Thus, by using LD element 27,
high-power LD light emitting device 20 can be configured.
[0044] The optical power density of LD element 27 is, for example,
0.5 W/mm.sup.2 or more from the viewpoint of increasing the power
of LD light emitting device 20. The optical power density may be 2
W/mm.sup.2 or more, 3 W/mm.sup.2 or more, and 10 W/mm.sup.2 or
more. On the other hand, if the optical power density is too high,
an amount of heat generated from the phosphor irradiated with light
increases, which may adversely affect LD light emitting device 20.
Thus, the optical power density may be 150 W/mm.sup.2 or less, 100
W/mm.sup.2 or less, 50 W/mm.sup.2 or less, and 20 W/mm.sup.2 or
less.
[0045] As LD element 27, for example, one that emits light in a
region extending from the lower end of the ultraviolet region to
yellow region, that is, one that has a peak of the light emission
spectrum in the wavelength region of 400 nm to 500 nm is used. For
example, an LD element that emits blue-violet light or an LD
element that emits blue light can be used. In this embodiment, the
case where LD element 27 emits blue light will be described.
LD Wavelength Conversion Member
[0046] LD wavelength conversion member 25 is configured by using
binder 24. Binder 24 is a medium such as a resin, glass, or
transparent crystal. Binder 24 may be a single material or may be a
different material depending on the location.
[0047] LD wavelength conversion member 25 contains a phosphor. The
phosphor converts light emitted from LD element 27 into light
having a longer wavelength. The phosphor of LD wavelength
conversion member 25 is configured by mixing red phosphor 21 and at
least one of yellow phosphor 22 and green phosphor 23. As red
phosphor 21, the red phosphor according to Embodiment 1 is used. As
yellow phosphor 22 and green phosphor 23, those phosphors
exemplified in Embodiment 2 can be used. In this embodiment, the
case where LD wavelength conversion member 25 is configured by
mixing three types of red phosphor 21, yellow phosphor 22, and
green phosphor 23 is particularly described. The mixing ratio of
the three types of phosphors can be appropriately adjusted
according to the desired color tone of white light, the light
emission intensity of each phosphor, and the like.
[0048] Blue light emitted from LD element 27 passes through
incident optical system 26 and is converted into red light, yellow
light, and green light by red phosphor 21, yellow phosphor 22, and
green phosphor 23 in LD wavelength conversion member 25,
respectively. White light is obtained by mixing blue light, which
is emitted from LD element 27 and is not absorbed by the three
types of phosphors described above, and red light, yellow light,
and green light that are converted by red phosphor 21, yellow
phosphor 22, and green phosphor 23, respectively.
[0049] As described above, according to the light emitting devices
of Embodiments 2 and 3, since the red phosphor according to
Embodiment 1 is used, it is possible to improve the quantum
efficiency at high power as compared with the light emitting device
of the related art. Furthermore, when configured as a white light
emitting device, high color rendering and color reproducibility can
be realized.
[0050] Hereinafter, Examples and Comparative Examples will be
specifically described.
Example 1
[0051] (1) As raw materials, 0.422 g of cerium oxide powder
(CeO.sub.2), 0.073 g of lithium oxide powder (Li.sub.2O), 19.505 g
of calcium oxide powder (CaO), and 2.000 g of barium fluoride
powder (BaF.sub.2) are weighed in one container.
Barium Fluoride is a Flux.
[0052] (2) These raw materials are mixed thoroughly. For mixing, a
device such as a ball mill can be used.
[0053] (3) The mixture is put into an alumina crucible and baked at
1400.degree. C. in an electric furnace at atmospheric pressure for
about 3 hours.
[0054] By doing as described above, in the red phosphor according
to Example 1, the red phosphor having the light emission spectrum
illustrated in FIG. 2 and expressed by the chemical formula
Ca.sub.0.993O:Ce.sub.0.007, Li.sub.0.007 can be obtained.
Examples 2 to 5 and Comparative Examples 1 to 3
[0055] FIG. 5 is Table 1 showing values of x, y, and z, formulation
amounts of the raw materials, evaluation results, and the like in
the red phosphors that can be expressed by Ca.sub.zO:Ce.sub.x,
Li.sub.y of Examples 1 to 3. FIG. 6 is Table 2 showing values of x,
y, and z, formulation amounts of the raw materials, evaluation
results, and the like in the red phosphors that can be expressed by
Ca.sub.zO:Ce.sub.x, Li.sub.y of Example 4 and Comparative Examples
1 and 2. FIG. 7 is Table 3 showing values of x, y, and z,
formulation amounts of the raw materials, evaluation results, and
the like in the red phosphors that can be expressed by
Ca.sub.zO:Ce.sub.x, Li.sub.y of Example 1, Example 5, and
Comparative Example 3.
[0056] Examples 2 to 5 and Comparative Examples 1 to 3 are the same
as Example 1 except that the raw materials were manufactured
according to the formulation shown in Table 1 of FIG. 5, Table 2 of
FIG. 6, and Table 3 of FIG. 7 and the respective values of x, y,
and z in the red phosphor that can be expressed by the chemical
formula of Ca.sub.zO:Ce.sub.x, Li.sub.y are shown in Table 1 of
FIG. 5, Table 2 of FIG. 6, and Table 3 of FIG. 7.
Evaluation of Light Emission Characteristics in Long Wavelength
Region (560 to 700 nm)
[0057] The light emission spectrum of Examples 1 to 5 and
Comparative Examples 1 to 3 were measured by using a
spectrofluoro-photometer using an integrating sphere. The
synthesized red phosphor was placed at a predetermined position in
the integrating sphere, and the powder was irradiated with blue
light emitted from the blue LED light source attached to a
measuring device, and the light emission spectrum was measured.
Judgment Criteria
[0058] In the light emission spectrum, those having a light
emission peak wavelength of 560 nm or more and 700 nm or less were
regarded as "A" as having excellent light emission characteristics
in the long wavelength region. [0059] In the light emission
spectrum, those having a light emission peak wavelength of less
than 560 nm were regarded as "B" as having insufficient light
emission characteristics in the long wavelength region.
Evaluation of Light Emission Efficiency
[0060] External quantum efficiencies of Examples 1 to 5 and
Comparative Examples 1 to 3 were measured using the
spectrofluoro-photometer. The method is the same as above.
Judgment Criteria
[0061] Since the external quantum efficiency of Example 1 showed
the highest value, a relative value when Example 1 was used as the
reference of the external quantum efficiency was evaluated as the
light emission efficiency. The relative value was calculated by
dividing the value of the external quantum efficiency of each
Example by the value of the external quantum efficiency of Example
1. When the relative value is 0.5 or less, light emission of the
red phosphor is weak, and thus if the red phosphor is irradiated
with the light source of the light emitting device, light emission
from the light source becomes strong and color rendering cannot be
ensured. Therefore, the judgment criteria are set as follows.
[0062] In a case where the relative value when the value of the
external quantum efficiency of Example 1 is used as the reference
is larger than 0.5, the judgment was set to "A" as having a range
of high light emission efficiency. [0063] In a case where the
relative value when the value of the external quantum efficiency of
Example 1 is used as the reference is 0.5 or less, the judgment was
set to "B" as having a range of low light emission efficiency.
Comprehensive Judgment Criteria
[0064] In Examples 1 to 5 and Comparative Examples 1 to 3,
comprehensive judgment was performed in consideration of both the
light emission characteristics in the long wavelength region and
the judgment of the evaluation of light emission efficiency. [0065]
When the judgment of the light emission characteristics in the long
wavelength region was "A" and the judgment of the light emission
efficiency was "A", the red phosphor was regarded as having
excellent light emission characteristics and light emission
efficiency in the long wavelength region, and the comprehensive
judgment was set to "A". [0066] In a case other than the case
described above, that is, when the judgment of one of the light
emission spectrum and the light emission efficiency is "B", it was
regarded that the function as the red phosphor cannot be
sufficiently exerted when the red phosphor was mounted on the light
emitting device, and the comprehensive judgment was set to "B".
[0067] The following can be said from Examples 1, 2 and 3 shown in
Table 1 of FIG. 5.
[0068] In the red phosphor that can be expressed by the chemical
formula of Ca.sub.zO:Ce.sub.x, Li.sub.y, it can be said that the
value of z is 1-x-y.ltoreq.z.ltoreq.1-x, and the red phosphor has
excellent light emission characteristics and light emission
efficiency in the wavelength region.
[0069] The following can be said from Example 4 and Comparative
Examples 1 and 2 shown in Table 2 of FIG. 6.
[0070] In the red phosphor that can be expressed by the chemical
formula of Ca.sub.zO:Ce.sub.x, Li.sub.y, it can be said that the
range of x value is 0<x<0.2, and the red phosphor has
excellent light emission characteristics and light emission
efficiency in the wavelength region. When x=0, that is, when Ce is
not contained, it cannot be a phosphor because light emission
center does not exist.
[0071] The following can be said from Examples 1 and 5 and
Comparative Example 3 shown in Table 3 of FIG. 7.
[0072] In the red phosphor that can be expressed by the chemical
formula of Ca.sub.zO:Ce.sub.x, Li.sub.y, it can be said that the
range of y value is 0.ltoreq.y<0.2, and the red phosphor has
excellent light emission characteristics and light emission
efficiency in the wavelength region.
Comparative Example 4
[0073] (1) Ca.sub.3N.sub.2 powder, Si.sub.3N.sub.4 powder, AlN
powder, and EuN powder were prepared as starting raw materials.
[0074] (2) Ca.sub.3N.sub.2 powder, Si.sub.3N.sub.4 powder, AlN
powder, and EuN powder were weighed so as to have a composition
expressed by the general formula Ca.sub.0.97Eu.sub.0.03AlSiN.sub.3,
and these powders were mixed. As a mixing method, dry mixing using
a mortar was performed in a glove box under a nitrogen
atmosphere.
[0075] (3) The mixed raw material powder was put into a crucible
made of boron nitride. This raw material powder was baked at
1600.degree. C. for 2 hours in a nitrogen atmosphere.
[0076] (4) The baked sample was washed in a nitric acid solution
having a concentration of 10% for 1 hour.
[0077] By the method described above, Comparative Example 4
expressed by CASN:Eu was prepared.
Evaluation of Light Emission Lifetime
[0078] The light emission lifetimes of Examples 1, 2, and 5 and
Comparative Example 4 were measured with a light emission lifetime
measuring device (manufactured by Hamamatsu Photonics). Table 4 of
FIG. 8 shows 1/e light emission lifetimes of Examples 1, 2, and 5
and Comparative Example 4.
[0079] It was found that the 1/e light emission lifetimes of
Examples 1, 2, and 5 were about 50 ns, showing a value of 100 ns or
less. It is known that the 1/e light emission lifetime of Ce is
generally 10 ns to 100 ns. Therefore, it is considered that light
emission obtained from Examples 1, 2, and 5 is derived from Ce.
[0080] On the other hand, the 1/e light emission lifetime of
CASN:Eu, which is Comparative Example 4, was 820 ns. Light emission
lifetime affects brightness saturation. It is known that, as
compared with the red phosphor containing Ce, the red phosphor
containing Eu is likely to be saturated in brightness due to a
decrease in quantum efficiency during high-power excitation. The
red phosphors containing Ce of Examples 1, 2, and 5 are considered
to be less likely to be saturated brightness because the light
emission lifetime value thereof is significantly smaller than that
of CASN:Eu, and therefore, the red phosphors of Examples 1, 2, and
5 can be combined with a high-power excitation light source to
realize a high-power light emitting device.
[0081] In the present disclosure, appropriate combinations of any
of the various embodiments and/or examples described above are
included, and the effects exerted by the respective embodiments
and/or examples can be achieved.
[0082] The red phosphor according to the present disclosure is a
red phosphor having a light emission peak wavelength in the range
of 560 nm or more and 700 nm or less, a large amount of light
emission in a long wavelength region, and capable of suppressing a
decrease in light emission rate under irradiation with a high-power
light source. When this red phosphor is applied to a light source
emitting blue light, it can be used as a light emitting device
excellent in high color rendering, can be suitably used as a light
source for lighting, and has high industrial utility value.
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