U.S. patent application number 12/425913 was filed with the patent office on 2009-08-13 for method for producing nitridosilicate-based compound, nitridosilicate phosphor, and light-emitting apparatus using the nitridosilicate phosphor.
This patent application is currently assigned to PANASONIC CORPORATION. Invention is credited to Shozo OSHIO.
Application Number | 20090200515 12/425913 |
Document ID | / |
Family ID | 34622176 |
Filed Date | 2009-08-13 |
United States Patent
Application |
20090200515 |
Kind Code |
A1 |
OSHIO; Shozo |
August 13, 2009 |
METHOD FOR PRODUCING NITRIDOSILICATE-BASED COMPOUND,
NITRIDOSILICATE PHOSPHOR, AND LIGHT-EMITTING APPARATUS USING THE
NITRIDOSILICATE PHOSPHOR
Abstract
A nitridosilicate-based compound is produced by reacting an
alkaline-earth metal compound capable of generating an
alkaline-earth metal oxide by heating or a rare earth compound
capable of generating a rare earth oxide by heating with at least a
silicon compound, while the alkaline-earth metal compound or the
rare earth compound is being reduced and nitrided by the reaction
with carbon in an atmosphere of nitriding gas. Because of this, a
nitridosilicate-based compound of high quality can be produced
industrially at low cost.
Inventors: |
OSHIO; Shozo; (Osaka,
JP) |
Correspondence
Address: |
HAMRE, SCHUMANN, MUELLER & LARSON P.C.
P.O. BOX 2902-0902
MINNEAPOLIS
MN
55402
US
|
Assignee: |
PANASONIC CORPORATION
Osaka
JP
|
Family ID: |
34622176 |
Appl. No.: |
12/425913 |
Filed: |
April 17, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10576946 |
Apr 25, 2006 |
7537710 |
|
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PCT/JP2004/017431 |
Nov 17, 2004 |
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12425913 |
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Current U.S.
Class: |
252/301.4F ;
423/263; 423/324; 423/328.1; 423/331 |
Current CPC
Class: |
C04B 2235/3206 20130101;
C09K 11/7734 20130101; C01P 2002/72 20130101; C04B 2235/46
20130101; C01P 2002/84 20130101; C04B 2235/3224 20130101; C04B
35/597 20130101; C09K 11/0883 20130101; C04B 2235/3852 20130101;
C04B 2235/425 20130101; C04B 2235/3208 20130101; C04B 35/6265
20130101; C01B 21/0602 20130101; C04B 35/6268 20130101; C04B
2235/3229 20130101; C04B 2235/3873 20130101; C01P 2002/54 20130101;
C04B 35/584 20130101; C04B 2235/3213 20130101; C04B 2235/3215
20130101; C04B 2235/6582 20130101 |
Class at
Publication: |
252/301.4F ;
423/324; 423/328.1; 423/331; 423/263 |
International
Class: |
C09K 11/59 20060101
C09K011/59; C01B 33/24 20060101 C01B033/24; C01B 33/26 20060101
C01B033/26; C01F 17/00 20060101 C01F017/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 19, 2003 |
JP |
2003-389695 |
May 19, 2004 |
JP |
2004-149616 |
Claims
1-17. (canceled)
18. A method for producing a compound by a reducing nitriding
reaction in which a sintering material is reduced and nitrided by a
reaction with carbon in an atmosphere of nitriding gas, wherein the
compound is a nitridosilicate-based compound, and the
nitridosilicate-based compound is a compound containing at least an
alkaline-earth metal element or a rare earth element, silicon, and
nitrogen as main constituent elements, and excluding SIALON
represented by a general formula:
M'.sub.p/2Si.sub.12-p-qAl.sub.p+qO.sub.qN.sub.16-q (where M' is Ca
or Ca combined with Sr; q is 0 to 2.5; and p is 1.5 to 3).
19. The method for producing a compound according to claim 18,
wherein the nitridosilicate-based compound is any compound selected
from nitridosilicate, oxonitridosilicate, nitridoaluminosilicate,
and oxonitridoaluminosilicate.
20. The method for producing a compound according to claim 18,
wherein the nitridosilicate-based compound is a highly nitrided
nitridosilicate-based compound, and the highly nitrided
nitridosilicate-based compound is a nitridosilicate-based compound
in which the number of atoms of oxygen is smaller than that of
alkaline-earth metal per mol of the nitridosilicate-based compound
or a nitridosilicate-based compound in which the number of atoms of
oxygen is smaller than the number obtained by multiplying the
number of atoms of rare earth metal by 1.5 per mol of the
nitridosilicate-based compound.
21. The method for producing a compound according to claim 20,
wherein the nitridosilicate-based compound is at least one compound
selected from M.sub.2Si.sub.5N.sub.8, MSi.sub.7N.sub.10,
M.sub.2Si.sub.4AlON.sub.7, MSiN.sub.2, and CaAlSiN.sub.3, and the M
is at least one element selected from Mg, Ca, Sr, and Ba.
22. The method for producing a compound according to claim 18,
wherein the nitriding gas is at least one gas selected from nitride
gas and ammonia gas.
23. The method for producing a compound according to claim 22,
wherein the carbon has any shape selected from solid-state carbon,
amorphous carbon, and carburizing gas.
24. The method for producing a compound according to claim 18,
wherein the sintering material contains at least one compound
selected from an alkaline-earth metal compound capable of
generating an alkaline-earth metal oxide MO (where M is at least
one element selected from Mg, Ca, Sr, and Ba; O is an oxygen
element) by heating and a rare earth compound capable of generating
a rare earth oxide LnO or Ln.sub.2O.sub.3 (where Ln is at least one
element selected from rare earth elements of atomic numbers 21, 39,
and 57-71; O is an oxygen element), and a silicon compound.
25. The method for producing a compound according to claim 24,
wherein the alkaline-earth metal compound is at least one
alkaline-earth metal compound selected from a carbonate, an
oxalate, an oxide, and a hydride of alkaline earth metal.
26. The method for producing a compound according to claim 24,
wherein the rare earth compound is at least one rare earth compound
selected from a carbonate, an oxalate, an oxide, and a hydride of a
rare earth element.
27. The method for producing a compound according to claim 24,
wherein the silicon compound is at least one silicon compound
selected from silicon nitride, silicon oxynitride, silicon oxide,
and silicon diimide.
28. The method for producing a compound according to claim 18,
wherein the reaction is performed by heating.
29. The method for producing a compound according to claim 28,
wherein a reaction temperature is 1400.degree. C. to 2000.degree.
C.
30. The method for producing a compound according to claim 18,
wherein the compound is a phosphor.
31. The method for producing a compound according to claim 30,
wherein the phosphor contains at least one element selected from
Ce, Pr, Eu, Tb, and Mn.
32. The method for producing a compound according to claim 31,
wherein a reaction atmosphere is a reducing atmosphere using
hydrogen.
33. The method for producing a compound according to claim 30,
wherein the phosphor is excited with light having an emission peak
in a near-ultraviolet or blue wavelength region of more than 340 nm
to 500 nm and converts the light into visible light with a
wavelength longer than a peak wavelength of the light.
34. A phosphor containing a compound obtained by the production
method according to claim 20 as a phosphor base material, and
containing an element that is to be a luminescent center.
35. The phosphor according to claim 34, wherein the compound
contains alkaline earth metal as a main component and Eu.sup.2+
ions or Ce.sup.3+ ions as the luminescent center.
36. A light-emitting apparatus using the phosphor according to
claim 34 as a light-emitting source.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of application Ser. No.
10/576,946, filed Apr. 25, 2006, which is a U.S. National Stage
Application based on PCT/JP2004/017431, filed Nov. 17, 2004, which
applications are incorporated thereby reference.
TECHNICAL FIELD
[0002] The present invention relates to a method for producing a
nitridosilicate-based compound (e.g., compounds containing at least
an alkaline-earth metal element or a rare earth element, a silicon
element, and a nitrogen element, such as nitridosilicates,
oxonitridosilicates, nitridoaluminosilicates,
oxonitridoaluminosilicates, and the like) applicable as a ceramic
material, a phosphor material, or the like; a nitridosilicate
phosphor; and a light-emitting apparatus using the nitridosilicate
phosphor.
BACKGROUND ART
[0003] Conventionally, a nitridosilicate-based compound containing
as major elements at least (1) an alkaline-earth metal element M
(where M is at least one element selected from Mg, Ca, Sr, and Ba),
(2) silicon, and (3) nitrogen, and a nitridosilicate-based compound
containing as major elements at least (1) a rare earth element Ln
(where Ln is at least one element selected from rare earth elements
of atomic numbers 21, 39, and 57-71), (2) silicon, and (3) nitrogen
are known.
[0004] Examples of the above-mentioned nitridosilicate-based
compound include Sr.sub.2Si.sub.5N.sub.8, Ba.sub.2Si.sub.5N.sub.8
(see Patent documents 1-3, and Non-patent document 1 described
below), BaSi.sub.7N.sub.10 (see Patent documents 1-3 described
below), SrSiAl.sub.2O.sub.3N.sub.2, Sr.sub.2Si.sub.4AlON.sub.7,
La.sub.3Si.sub.6N.sub.11 (see Patent document 4 described below),
Eu.sub.2Si.sub.5N.sub.8, EuYbSi.sub.4N.sub.7 (see Non-patent
document 2 described below), (Ba, Eu).sub.2Si.sub.5N.sub.8 (see
Non-patent document 3 described below),
Ce.sub.4(Si.sub.4O.sub.4N.sub.6)O,
Sr.sub.3Ce.sub.10Si.sub.18Al.sub.12O.sub.18N.sub.36 (see Non-patent
document 4 described below), CaSiN.sub.2 (see Non-patent document 5
described below), and the like. In the present specification,
SIALON (see Patent document 5 described below) represented by a
general formula: M.sub.p/2Si.sub.12-p-qAl.sub.p+qO.sub.qN.sub.16-q
(where M is Ca or Ca combined with Sr; q is 0 to 2.5; and p is 1.5
to 3) is excluded.
[0005] It is known that the above-mentioned CaSiN.sub.2 becomes a
CaSiN.sub.2:Eu.sup.2+ phosphor emitting red light having an
emission peak in the vicinity of 630 nm by being activated with
Eu.sup.2+ ions being a luminescent center. The following also is
known: the excitation spectrum of the above-mentioned phosphor has
a peak in the vicinity of 370 nm, and although the phosphor does
not emit red light with a high intensity at excitation of blue
light in a range of 440 nm to less than 500 nm, it emits red light
with a strong output at near-ultraviolet light excitation in a
range of 330 to 420 nm. Therefore, the application to a
light-emitting apparatus using a light-emitting element emitting
near-ultraviolet light as an excitation source is considered to be
promising (see Non-patent document 5 described below).
[0006] Furthermore, the following also is known: the
above-mentioned nitridosilicate-based compound can be applied as a
phosphor material as well as a ceramic material, and the
above-mentioned nitridosilicate-based compound, for example,
containing Eu.sup.2+ ions and Ce.sup.3+ ions becomes a
high-efficiency phosphor (see Patent documents 1 to 6 described
below).
[0007] Furthermore, it also is known that the above-mentioned
high-efficiency phosphor composed of a nitridosilicate-based
compound is suitable as an LED light source, since it is excited
with near-ultraviolet light to blue light, and emits visible light
of blue, green, yellow, orange, or red (see Patent documents 1 to
3, and Non-patent document 5 described below).
[0008] Conventionally, in order to produce the above-mentioned
nitridosilicate-based compound, a production method has been used,
in which alkaline-earth metal (metal Ca, metal Sr, metal Ba, etc.)
or a nitride of alkaline-earth metal (Ca.sub.3N.sub.2,
Sr.sub.3N.sub.2, Ba.sub.3N.sub.2, etc.) is used as a supply source
of alkaline-earth metal, and rare earth metal (metal La, metal Ce,
metal Eu, etc.) is used as a supply source of a rare earth element,
without using a reducing agent (solid-state carbon, etc. described
below) excluding alkaline-earth metal and rare earth metal (see
Patent documents 1-6, and Non-patent documents 1-4).
[0009] On the other hand, conventionally, the use of a phosphor of
a nitridosilicate-based compound produced by such a production
method in a light-emitting apparatus such as an LED light source
has been studied.
[0010] (Patent document 1) JP2003-515655A
[0011] (Patent document 2) JP2003-515665A
[0012] (Patent document 3) JP2003-322474A
[0013] (Patent document 4) JP2003-206481A
[0014] (Patent document 5) JP2003-203504A
[0015] (Patent document 6) JP2003-124527A
[0016] (Non-patent document 1) T. Schlieper et al., Z. an org.
allg. Chem., Vol. 621, (1995), pages 1380-1384
[0017] (Non-patent document 2) H. Huppertz and W. Schnick, Acta
Cryst., Vol. 53, (1997), pages 1751-1753
[0018] (Non-patent document 3) H. A. Hoppe et al., J. Phys. Chem.
Solids, Vol. 61 (2000), pages 2001-2006
[0019] (Non-patent document 4) W. Schnick, Int. J. Inorg. Mater.,
Vol. 3 (2001), pages 1267-1272
[0020] (Non-patent document 5) K. Ueda et al., Extended Abstracts
of 71st Meeting of The Japan Society of Electrochemistry (2004),
page 75
[0021] However, according to the conventional method for producing
a nitridosilicate-based compound, above all, a method for producing
a highly nitrided nitridosilicate-based compound (e.g.,
M.sub.2Si.sub.5N.sub.8, MSi.sub.7N.sub.10,
M.sub.2Si.sub.4AlON.sub.7, MSiN.sub.2 (where M is at least one
element selected from Mg, Ca, Sr, and Ba), etc.) with a small
number of oxygen atoms, in particular, a nitridosilicate-based
compound containing substantially no oxygen component,
alkaline-earth metal or rare earth metal, which is chemically
unstable and has the danger of ignition, or a nitride of
alkaline-earth metal or rare earth nitride, which is difficult to
obtain, is very expensive, and is difficult to handle, is used as a
supply source of alkaline-earth metal or a rare earth element.
Therefore, the above-mentioned method has the following problems,
which makes it very difficult to industrially produce a
nitridosilicate-based compound.
[0022] (1) It is difficult to mass-produce a nitridosilicate-based
compound.
[0023] (2) It is difficult to produce a high purity compound of
high quality with satisfactory reproducibility.
[0024] (3) It is difficult to provide an inexpensive compound.
[0025] Since the conventional production method has such problems,
the conventional nitridosilicate-based compound has the following
problems: (1) low purity due to the presence of a large amount of
impurity oxygen; (2) low material performance such as low emission
performance of a phosphor caused by the low purity; (3) high cost;
and the like. For example, the conventional light-emitting
apparatus using the conventional nitridosilicate-based phosphor as
a light-emitting source has the following problems: (1) low
luminous flux and brightness; (2) high cost; and the like.
DISCLOSURE OF INVENTION
[0026] The present invention is a method for producing a
nitridosilicate-based compound, including reacting a material
containing an alkaline-earth metal compound capable of generating
an alkaline-earth metal oxide MO (where M is at least one element
selected from Mg, Ca, Sr, and Ba; and O is oxygen) by heating, a
silicon compound, and carbon in an atmosphere of nitriding gas.
[0027] Furthermore, the present invention is a method for producing
a nitridosilicate-based compound, including reacting a material
containing a rare earth compound capable of generating a rare earth
oxide LnO or Ln.sub.2O.sub.3 (where Ln is at least one element
selected from rare earth elements of atomic numbers 21, 39, and
57-71; and O is oxygen) by heating, a silicon compound, and carbon
in an atmosphere of nitriding gas.
[0028] Furthermore, the present invention is a method for producing
a nitridosilicate-based compound, including reacting a material
containing at least one selected from alkaline-earth metal, a
nitride of alkaline earth metal, rare earth metal, and a rare earth
nitride, a silicon compound, and carbon in an atmosphere of
nitriding gas.
[0029] Furthermore, the present invention is a nitridosilicate
phosphor including a nitridosilicate compound represented by a
general formula: MSiN.sub.2 as a phosphor base material, and
Eu.sup.2+ ions as a luminescent center, wherein a main component of
the M is Ba.
[0030] Furthermore, the present invention is a light-emitting
apparatus using the above-mentioned nitridosilicate-based phosphor
as a light-emitting source
BRIEF DESCRIPTION OF DRAWINGS
[0031] FIG. 1 is a cross-sectional view showing an exemplary
light-emitting apparatus using a nitridosilicate-based
phosphor.
[0032] FIG. 2 shows an X-ray diffraction pattern of a
nitridosilicate-based compound according to Example 1.
[0033] FIG. 3 shows emission spectra of nitridosilicate-based
compounds according to Example 1 and Comparative Example 1.
[0034] FIG. 4 shows an X-ray diffraction pattern of a
nitridosilicate-based compound according to Example 2.
[0035] FIG. 5 shows an emission/excitation spectrum of a
nitridosilicate-based compound according to Example 3.
BEST MODE FOR CARRYING OUT THE INVENTION
[0036] According to the present invention, a nitridosilicate-based
compound can be produced using an alkaline-earth metal salt, a rare
earth oxide, or the like, which is easy to handle and obtain, and
is inexpensive, as a supply source of alkaline-earth metal or a
rare earth element, without using alkaline-earth metal or a nitride
of alkaline-earth metal, and rare earth metal or a rare earth
nitride, which is chemically unstable, is difficult to handle in
the air, is difficult to obtain, and is expensive; and a
nitridosilicate-based compound with satisfactory material
performance and a phosphor using the same can be produced
industrially with satisfactory reproducibility at low cost.
[0037] Furthermore, the present invention also can provide a
nitridosilicate-based compound and a nitridosilicate-based phosphor
that are inexpensive and have high performance, and an applied
product (such as an LED light source) of a nitridosilicate-based
compound that is inexpensive and has high performance.
[0038] Hereinafter, the present invention will be described by way
of an embodiment.
[0039] According to an exemplary method for producing a
nitridosilicate-based compound (including a nitridosilicate-based
phosphor) of the present invention, an alkaline-earth metal
compound capable of generating an alkaline-earth metal oxide MO
(where M is at least one element selected from Mg, Ca, Sr, and Ba)
by heating is reacted with at least a silicon compound, while being
reduced and nitrided by the reaction with carbon in an atmosphere
of nitriding gas.
[0040] Furthermore, according to another exemplary method for
producing a nitridosilicate-based compound of the present
invention, a rare earth compound capable of generating a rare earth
oxide LnO or Ln.sub.2O.sub.3 (where Ln is at least one element
selected from rare earth elements of atomic numbers 21, 39, and
57-71) by heating is reacted with at least a silicon compound,
while being reduced and nitrided by the reaction with carbon in an
atmosphere of nitriding gas.
[0041] Thus, as a supply source of alkaline-earth metal or a rare
earth element constituting the above-mentioned
nitridosilicate-based compound, an alkaline-earth metal compound or
a rare earth compound that is inexpensive and easy to handle, such
as a carbonate, an oxalate, a hydride, and an oxide, can be
used.
[0042] Furthermore, a supply material (carbon, a silicon compound,
etc.) and supply gas (nitrogen gas, etc.) other than the
alkaline-earth metal or a rare earth element used for producing the
nitridosilicate-based compound also are relatively easy to obtain,
are easy to handle, and are inexpensive. Therefore, the
nitridosilicate-based compound can be provided with satisfactory
reproducibility at low cost.
[0043] Furthermore, a firing material can be reduced actively due
to the reaction with carbon as a reducing agent, and an oxygen
component in the firing material can be removed as carbon oxide gas
or carbon dioxide gas. Therefore, the mixed amount of impurity
oxygen in the nitridosilicate-based compound is decreased, the
purity of the nitridosilicate-based compound is enhanced, and
consequently, various performances can be exhibited more
highly.
[0044] The functional effect regarding the enhancement of material
performance is exhibited in the case of producing a highly nitrided
nitridosilicate-based compound in which the number of atoms of
oxygen is smaller than that of alkaline-earth metal, and a highly
nitrided nitridosilicate-based compound in which the number of
atoms of oxygen is smaller than the number obtained by multiplying
the number of atoms of rare earth metal by 1.5, per mol of the
nitridosilicate-based compound. In particular, the functional
effect becomes conspicuous in the production of a
nitridosilicate-based compound (e.g., M.sub.2Si.sub.5N.sub.8 and
M.sub.2Si.sub.5N.sub.8:Eu.sup.2+ phosphor, MSiN.sub.2 and
MSiN.sub.2:Eu.sup.2+ phosphor) containing no oxygen component.
[0045] Herein, the nitridosilicate-based compound of the present
invention refers to a compound containing at least an
alkaline-earth metal element or a rare earth element, silicon, and
nitrogen, such as nitridosilicates, oxonitridosilicates,
nitridoaluminosilicates, oxonitridoaluminosilicates, etc. In the
present specification, compounds having a SIALON-type crystal
structure are excluded.
[0046] The production method of the present invention is a method
for producing a nitridosilicate-based compound that can be called,
for example, a reducing nitriding reaction method. In particular,
the production method of the present invention is suitable for
industrial production of a powder-shaped nitridosilicate-based
compound.
[0047] The above-mentioned alkaline-earth metal compound is not
particularly limited as long as it is an alkaline-earth metal
compound capable of generating the above-mentioned alkaline-earth
metal oxide MO. In terms of the availability of a high-purity
compound, the ease of handling in the air, the cost, and the like,
the above-mentioned alkaline-earth metal compound preferably is at
least one selected from a carbonate, an oxalate, a nitrate, a
sulfate, an acetate, an oxide, a peroxide, and a hydride of
alkaline-earth metal; more preferably is a carbonate, an oxalate,
an oxide, and a hydride of an alkaline-earth metal; and most
preferably a carbonate of alkaline-earth metal. Furthermore, for
the purpose of obtaining a high-purity nitridosilicate-based
compound, preferable M is at least one element selected from Sr and
Ba.
[0048] There is no particular limit to the shape of the
alkaline-earth metal compound, and a powder shape, a lump shape, or
the like may be selected appropriately. For the purpose of
obtaining a powder-shaped nitridosilicate-based compound, a
preferable shape is powder.
[0049] The rare earth compound is not particularly limited as long
as it is capable of generating the above-mentioned rare earth oxide
LnO or Ln.sub.2O.sub.3. In terms of the availability of a
high-purity compound, the ease of handling in the air, the cost,
etc., the rare earth compound preferably is at least one selected
from a carbonate, an oxalate, a nitrate, a sulfate, an acetate, an
oxide, a peroxide, and a hydride of a rare earth element; more
preferably is a carbonate, an oxalate, an oxide, and a hydride of a
rare earth element; and most preferably is a rare earth oxide.
[0050] There is no particular limit to the shape of the rare earth
compound, and a powder shape, a lump shape, or the like may be
selected appropriately. For the purpose of obtaining a
powder-shaped nitridosilicate-based compound, a preferable shape is
powder.
[0051] Furthermore, there is no particular limit to the silicon
compound, as long as it is capable of forming a
nitridosilicate-based compound by the above-mentioned reaction. For
the same reason as that in the case of the above-mentioned
alkaline-earth metal compound and rare earth compound, the silicon
compound preferably is silicon nitride (Si.sub.3N.sub.4), silicon
oxynitride (Si.sub.2ON.sub.2), silicon oxide (SiO or SiO.sub.2),
silicon diimide (Si(NH).sub.2); more preferably is at least one
silicon compound selected from silicon nitride and silicon diimide;
and most preferably is silicon nitride.
[0052] There is no particular limit to the shape of the
above-mentioned silicon compound, and a powder shape, a lump shape,
or the like may be selected appropriately. For the purpose of
obtaining a powder-shaped nitridosilicate-based compound, a
preferable shape is powder.
[0053] According to the production method of the present invention,
the supply source of silicon may be elemental silicon. In this
case, elemental silicon is reacted with nitrogen in an atmosphere
of nitriding gas to form a nitride compound (silicon nitride, etc.)
of silicon, and is reacted with the above-mentioned alkaline-earth
metal nitride and the above-mentioned rare earth nitride. For this
reason, according to the present invention, the silicon compound
includes elemental silicon.
[0054] There is no particular limit to the shape of the
above-mentioned carbon. A preferable shape is solid-state carbon,
and above all, graphite. However, the carbon may be amorphous
carbon (coals, coke, charcoal, gas carbon, etc.). In addition, for
example, hydrocarbon such as natural gas that is carburizing gas,
methane (CH.sub.4), propane (C.sub.3H.sub.8), butane
(C.sub.4H.sub.10), etc., and a carbon oxide such as carbon oxide
(CO) may be used as a carbon supply source.
[0055] In the case of using a firing container or a heat generator
made of carbon in a vacuum atmosphere or in a neutral atmosphere
such as an inert gas atmosphere, a part of the carbon may be
evaporated. However, in principle, it also is possible to use such
evaporated carbon as a reducing agent.
[0056] Regarding the above-mentioned solid-state carbon, there is
no particular limit to the size and shape. In terms of the
availability, preferable solid-state carbon is powder or grains
with a size of 1 .mu.m to 1 cm. The solid-state carbon with other
sizes and shapes may be used. Solid-state carbon in various shapes,
such as a powder shape, a grain shape, a lump shape, a plate shape,
a bar shape, and the like, can be used. There is no particular
limit to the purity of the solid-state carbon. For the purpose of
obtaining a nitridosilicate-based compound of high quality, the
purity of the solid-state carbon preferably is as high as possible.
For example, high purity carbon with a purity of 99% or higher,
preferably 99.9% or higher is used.
[0057] The above-mentioned solid-state carbon to be reacted also
may function as a heat generator (carbon heater) or a firing
container (carbon crucible, etc.). The above-mentioned carbon used
as a reducing agent may be used in combination with the materials
for a nitridosilicate-based compound, or merely may be brought into
contact therewith.
[0058] Furthermore, there is no particular limit to the nitriding
gas as long as it is capable of effecting a nitriding reaction. In
terms of the availability of high-purity gas, the ease of handling,
the cost, etc., the nitriding gas preferably is at least one kind
of gas selected from nitrogen gas and ammonia gas, and more
preferably is nitrogen gas.
[0059] The preferable reaction atmosphere containing nitriding gas
is an atmospheric pressure atmosphere for the reason of the
availability of simple facilities. However, any of a high-pressure
atmosphere, a pressurizing atmosphere, a reduced-pressure
atmosphere, and a vacuum atmosphere may be used. The preferable
reaction atmosphere for the purpose of enhancing the performance of
a compound (or a phosphor) to be obtained is a high-pressure
atmosphere (e.g., 2 to 100 atmospheres), and considering the
handling of an atmosphere, the preferable reaction atmosphere
mainly contains nitrogen gas (5 to 20 atmospheres). In such a
high-pressure atmosphere, the decomposition of a compound (nitride)
generated during firing at high temperature can be prevented or
suppressed, and the compositional shift of a compound to be
obtained is suppressed, whereby a compound with high performance
can be produced. For the purpose of promoting decarbonization of a
reactant (fired material), a small amount or trace amount of water
vapor may be contained in the above-mentioned reaction
atmosphere.
[0060] Furthermore, in order to enhance the reactivity between the
reactants (compound materials), flux may be added for the reaction.
As the flux, an alkaline metal compound (Na.sub.2CO.sub.3, NaCl,
LiF), a halogen compound (SrF.sub.2, CaCl.sub.2, etc.), etc. can be
appropriately selected for use.
[0061] The major features of the present invention are as follows:
(1) as the material for a nitridosilicate-based compound,
alkaline-earth metal or rare earth metal, or a nitride of
alkaline-earth metal or a rare earth nitride is not used
substantially; (2) instead, an alkaline-earth metal compound or a
rare earth compound capable of generating an alkaline-earth metal
oxide or a rare earth oxide by heating is used; (3) an oxygen
component contained in these compounds is removed by the reaction
with carbon, preferably, solid-state carbon; (4) while the
alkaline-earth metal compound or rare earth compound is being
nitrided by the reaction with nitriding gas; (5) the alkaline-earth
metal compound or rare earth compound is reacted with a silicon
compound, whereby a nitridosilicate-based compound is produced.
[0062] According to the production method of the present invention,
the above-mentioned silicon compound is exposed to nitriding gas,
and reacts with the above-mentioned alkaline-earth metal compound
or rare earth compound while being nitrided during a reaction
process between materials. Therefore, the method for producing a
nitridosilicate-based compound of the present invention can be
considered substantially as a method for producing a
nitridosilicate-based compound by at least reacting (1) an
alkaline-earth metal oxide, (2) carbon, particularly, solid-state
carbon, (3) nitrogen, and (4) silicon nitride with each other, or a
method for producing a nitridosilicate-based compound by at least
reacting (1) a rare earth oxide, (2) carbon, particularly,
solid-state carbon, (3) nitrogen, and (4) silicon nitride with each
other.
[0063] Furthermore, when an aluminum compound (aluminum nitride,
aluminum oxide, aluminum hydroxide, etc.) is reacted further in the
above-mentioned method for producing a nitridosilicate-based
compound, a nitridoaluminosilicate compound and an
oxonitridoaluminosilicate compound also can be produced.
[0064] Furthermore, when a transition metal or a transition metal
compound, such as metal zinc or a zinc compound (zinc oxide, zinc
nitride, etc.), metalic titanium or a titanium compound (titanium
oxide, titanium nitride, etc.), metalic zirconium or a zirconium
compound (zirconium oxide, zirconium nitride, etc.), metalic
hafnium or a hafnium compound (hafnium oxide, hafnium nitride,
etc.), metalic tungsten or a tungsten compound (tungsten oxide,
tungsten nitride, etc.), or metalic tin or a tin compound (tin
oxide, tin nitride, etc.), is reacted further in the
above-mentioned method for producing a nitridosilicate-based
compound of the present invention, a nitridosilicate-based compound
containing these transition metal elements also can be produced.
Furthermore, when a nitridosilicate-based compound is produced by
reacting phosphorus or a phosphorus compound (phosphorus pentoxide,
phosphorus pentanitride, phosphates, diammonium hydrogenphosphate,
etc.), a nitridosilicate-based compound containing phosphorus can
be produced. When a nitridosilicate-based compound is produced by
reacting boron or a boron compound (boric acid, boron nitride,
boric anhydride, etc.), a nitridosilicate-based compound containing
boron also can be produced.
[0065] The reaction in the production method of the present
invention is started and maintained by an operation of adding
energy to a reaction material, for example, by heating.
[0066] According to the method for producing a
nitridosilicate-based compound of the present invention, the
reaction temperature is in a range of preferably 1400.degree. C. to
2000.degree. C., and more preferably 1500.degree. C. to
1800.degree. C. Furthermore, the reaction may be performed in
several sections. Thus, the above-mentioned alkaline-earth metal
compound or rare earth compound becomes an alkaline-earth metal
oxide or a rare earth oxide by heating, and furthermore, due to the
reaction with carbon, the alkaline-earth metal oxide or the rare
earth oxide is reduced while generating carbon oxide or carbon
dioxide. Furthermore, the reduced alkaline-earth metal oxide or
rare earth oxide reacts with other compounds such as the
above-mentioned silicon compound, gas, and the like, while being
nitrided with nitriding gas to form a nitride. Thus, a
nitridosilicate-based compound is generated.
[0067] At a temperature lower than the above-mentioned temperature
range, the above-mentioned reaction and reduction may be
insufficient, which makes it difficult to obtain a
nitridosilicate-based compound of high quality. At a temperature
higher than the above-mentioned temperature range, a
nitridosilicate-based compound is decomposed or melted, which makes
it difficult to obtain a compound with a predetermined composition
and shape (powder shape, molded shape, etc.), and makes it
necessary to use an expensive heat generator and a heat-insulating
material with high heat resistance for a production facility,
resulting in an increase in facility cost. Consequently, it becomes
difficult to provide a nitridosilicate-based compound at low
cost.
[0068] The amounts of the materials used in the production method
of the present invention may be adjusted in accordance with the
composition of an intended nitridosilicate-based compound. The
amount of carbon preferably is set to be an excess so as to
completely reduce a predetermined amount of oxygen in an oxygen
component contained in each material to be used.
[0069] According to the production method of the present invention,
a number of nitridosilicate-based compounds described above, such
as CaSiN.sub.2, BaSiN.sub.2, Sr.sub.2Si.sub.5N.sub.8,
Ba.sub.2Si.sub.5N.sub.8, (Sr, Eu).sub.2Si.sub.5N.sub.8,
Eu.sub.2Si.sub.5N.sub.8, BaSi.sub.7N.sub.10,
Sr.sub.2Si.sub.4AlON.sub.7, and CaAlSiN.sub.3, can be produced.
Such a nitridosilicate-based compound can be used as a phosphor as
well as a ceramic member, etc. Since a nitridosilicate-based
compound such as M.sub.2Si.sub.5N.sub.8, MSiN.sub.2, and the like
function as a phosphor base material of a high-efficiency phosphor,
the method for producing a nitridosilicate-based compound of the
present invention can be applied widely to a method for producing a
nitridosilicate-based phosphor.
[0070] Furthermore, as another exemplary method for producing a
nitridosilicate-based compound of the present invention, it is
possible to adopt a method for reacting a material containing at
least one selected from alkaline-earth metal, a nitride of
alkaline-earth metal, rare earth metal, and a rare earth nitride, a
silicon compound, and carbon in an atmosphere of nitriding gas.
More specifically, when carbon as a reducing agent is added to
alkaline-earth metal (M) or a nitride (M.sub.3N.sub.2) of
alkaline-earth metal and a silicon compound such as silicon nitride
(Si.sub.3N.sub.4), or rare earth metal or a nitride of rare earth
metal and a silicon compound, which are used for forming a
nitridosilicate-based compound, and fired in an atmosphere of
nitriding gas, impurity oxygen can be removed as carbon oxide gas
(CO) during firing, and the impurity oxide can be prevented or
suppressed from being mixed in the compound. Therefore, a
nitridosilicate-based compound with high purity and high
performance can be produced.
[0071] In order to produce a nitridosilicate-based phosphor, metal
or a compound containing an element to be the luminescent center
only needs to be at least reacted during the above-mentioned
reaction process. Examples of such an element include lanthanide of
atomic numbers 58-60, or 62-71 and transition metals (in
particular, Ce, Pr, Eu, Tb, and Mn). Examples of a compound
containing such an element include an oxide, a nitride, a hydride,
a carbonate, an oxalate, a nitrate, a sulfate, a halide, a
phosphate, and the like of the above-mentioned lanthanide and
transition metal.
[0072] More specifically, the present invention also may be
directed to a method for producing a nitridosilicate-based phosphor
by further reacting at least one of a metalic lanthanide and a
lanthanide compound, excluding metalic lanthanum or metalic
promethium, or a lanthanum compound and a promethium compound; or a
method for producing a nitridosilicate-based phosphor by further
reacting at least one of transition metal and a transition metal
compound.
[0073] According to a method for producing a nitridosilicate-based
phosphor containing lanthanide ions such as Ce.sup.3+, Pr.sup.3+,
Eu.sup.2+, and Tb.sup.3+, or Mn.sup.2+ ions as a luminescent
center, the reaction atmosphere preferably is a reducing
atmosphere. An atmosphere of mixed gas of nitrogen and hydrogen is
particularly preferable because a strong reducing force can be
obtained easily at relatively low cost. Thus, the generation of
ions, such as Ce.sup.4+, Pr.sup.4+, Eu.sup.3+, Tb.sup.4+,
Mn.sup.3+, etc., which do not substantially function as the
luminescent center of a desired high-efficiency phosphor can be
prevented, and the concentration of lanthanide ions or transition
metal ions, such as Ce.sup.3+, Pr.sup.3+, Eu.sup.2+, Tb.sup.3+,
Mn.sup.2+, etc., which emit high-efficiency light, is increased.
Therefore, a high-efficiency nitridosilicate-based phosphor can be
provided. Furthermore, in a reducing atmosphere using hydrogen, due
to the effect of decarbonization of hydrogen gas, it is expected
that the purity of a fired material is enhanced.
[0074] According to the method for producing a
nitridosilicate-based compound of the present invention,
high-efficiency nitridosilicate-based phosphor can be provided at
low cost. Typical examples of the above-mentioned
nitridosilicate-based phosphor include MSiN.sub.2:Eu.sup.2+,
M.sub.2Si.sub.5N.sub.8:Eu.sup.2+, M.sub.2Si.sub.5N.sub.8:Ce.sup.3+,
Sr.sub.2Si.sub.4AlON.sub.7:Eu.sup.2+, and the like.
[0075] Such a nitridosilicate-based phosphor can be used as, for
example, (1) a light-emitting source of an LED light source for
illumination, (2) a wavelength conversion layer of a multi-color
display inorganic thin film EL (electroluminescence) panel
configured by using a blue phosphor such as
BaAl.sub.2S.sub.4:Eu.sup.2+ as a light-emitting layer and further
incorporating a wavelength conversion layer, (3) a light-emitting
source of warm color (yellow-orange-red) of a fluorescent lamp
(discharge lamp), and the like. Furthermore, the
nitridosilicate-based phosphor is excellent in temperature
characteristics and maintains high emission performance even under
a high temperature. Therefore, the above-mentioned light-emitting
apparatus with temperature characteristics enhanced can be provided
at low cost.
[0076] The method for producing a nitridosilicate-based phosphor of
the present invention is suitable for industrial production of a
phosphor, such as Sr.sub.2Si.sub.5N.sub.8:Eu.sup.2+,
Ba.sub.2Si.sub.5N.sub.8:Eu.sup.2+,
Sr.sub.2Si.sub.5N.sub.8:Ce.sup.3+,
Ba.sub.2Si.sub.5N.sub.8:Ce.sup.3+, CaSiN.sub.2:Eu.sup.2+,
BaSiN.sub.2:Eu.sup.2+, Sr.sub.2Si.sub.4AlON.sub.7:Eu.sup.2+, and
the like, for LED illumination, which is excited with
near-ultraviolet to blue light and emits high-efficiency warm color
based light (yellow-orange-red light).
[0077] A M.sub.2Si.sub.5N.sub.8:Eu.sup.2+ phosphor, and the like
emitting red light can be formed into an
M.sub.2Si.sub.5N.sub.8:Ce.sup.3+, Eu.sup.2+ phosphor by activating
Ce.sup.3+ ions together. For example, the excitation spectrum of
M.sub.2Si.sub.5N.sub.8:Eu.sup.2+ emitting red light and the
emission spectrum of M.sub.2Si.sub.5N.sub.8:Ce.sup.3+ emitting
yellow-green light are overlapped with each other. Therefore, due
to the above-mentioned activation of Ce.sup.3+ ions, the energy
transmission from Ce.sup.3+ ions to Eu.sup.2+ ions occurs, and in
connection therewith, the M.sub.2Si.sub.5N.sub.8:Ce.sup.3+,
Eu.sup.2+ phosphor has its excitation spectrum shape changed to
that similar to the excitation spectrum of the
M.sub.2Si.sub.5N.sub.8:Ce.sup.3+ phosphor, and becomes a red
phosphor exhibiting an emission efficiency higher than that of the
M.sub.2Si.sub.5N.sub.8:Eu.sup.2+ phosphor under the condition of
ultraviolet to near-ultraviolet excitation of 250 to 400 nm.
Therefore, the M.sub.2Si.sub.5N.sub.8:Ce.sup.3+, Eu.sup.2+ phosphor
becomes a more effective red phosphor than the
M.sub.2Si.sub.5N.sub.8:Eu.sup.2+ phosphor in a light-emitting
apparatus using ultraviolet light or near-ultraviolet light in such
a wavelength range as excited light.
[0078] The nitridosilicate-based compound produced by the
production method of the present invention can be produced using an
alkaline-earth metal compound or a rare earth compound, solid-state
carbon or carbon-based gas, a silicon compound, and nitriding gas,
which are inexpensive and easy to obtain and handle, so that the
nitridosilicate-based compound can be produced simply at low
cost.
[0079] Furthermore, a nitridosilicate-based compound produced by
the production method of the present invention, above all, a highly
nitrided nitridosilicate-based compound in which the number of
oxygen atoms is smaller than the number of atoms of alkaline-earth
metal or a highly nitrided nitridosilicate-based compound in which
the number of oxygen is smaller than the number obtained by
multiplying the number of atoms of rare earth metal by 1.5, in
particular, a nitridosilicate-based compound containing
substantially no oxygen component is produced while a firing
material is being reduced actively due to the reaction with carbon
to be a reducing agent and an oxygen component in the firing
material is removed as carbon oxide or carbon dioxide. Therefore,
the above-mentioned nitridosilicate-based compound has a small
mixed amount of impurity oxygen and high purity, and consequently,
exhibits high performance.
[0080] Thus, an applied product (LED light source, etc.) using a
nitridosilicate-based compound produced using the production method
of the present invention, which is inexpensive and has high
performance (high luminous flux, etc.), also can be provided.
[0081] Next, an embodiment of a light-emitting apparatus of the
present invention will be described with reference to the drawings.
FIG. 1 shows an example of a light-emitting apparatus (applied
product) using a nitridosilicate-based phosphor as a light-emitting
source. The light-emitting apparatus shown in FIG. 1 also is a
light source adopting an LED. FIG. 1 also is a cross-sectional view
showing an exemplary semiconductor light-emitting element used
often for an illumination or display apparatus.
[0082] FIG. 1 shows a semiconductor light-emitting element with a
configuration in which at least one light-emitting element 1 is
mounted on a sub-mount element 4 so as to be in conduction
therewith, and the light-emitting element 1 is sealed with a
package of a base material (e.g., resin, glass with a low melting
point, etc.) that contains at least the above-mentioned
nitridosilicate-based phosphor 2 and also functions as a phosphor
layer 3.
[0083] In FIG. 1, the light-emitting element 1 is a photoelectric
transducer for converting electric energy into light, to which a
light-emitting diode, a laser diode, a surface-emitting laser
diode, an inorganic electroluminescence element, an organic
electroluminescence element, and the like correspond. In
particular, in terms of a high output of a light source, a
light-emitting diode or a surface-emitting laser diode is
preferable. Basically, the wavelength of light emitted by the
light-emitting element 1 is not particularly limited, and may be in
a wavelength range (e.g., 250 to 550 nm) in which a
nitridosilicate-based phosphor can be excited. However, in order to
produce a light source that allows a nitridosilicate-based phosphor
to be excited with high efficiency and has high performance in
emitting white-based light in high demand, the light-emitting
element 1 is set to have an emission peak in a wavelength range of
more than 340 nm to 500 nm, preferably more than 350 nm to 420 nm
or more than 420 nm to 500 nm, more preferably more than 360 nm to
410 nm or more than 440 nm to 480 nm, i.e., in a near-ultraviolet
or blue wavelength region.
[0084] Furthermore, in FIG. 1, the phosphor layer 3 includes at
least the nitridosilicate-based phosphor 2. For example, the
phosphor layer 3 is configured by dispersing at least the
nitridosilicate-based phosphor 2 in a transparent base material
such as transparent resin (epoxy resin, silicon resin, etc.), glass
with a low melting point, or the like. The content of the
nitridosilicate-based phosphor 2 in the transparent base material
is, for example, preferably 5 to 80% by mass, and more preferably
10 to 60% by mass in the case of the above-mentioned transparent
resin. The nitridosilicate-based phosphor 2 contained in the
phosphor layer 3 is a light conversion material for absorbing a
part of or entire light emitted by the driven light-emitting
element 1 and converting the absorbed light into visible light
(blue, green, yellow, orange, or red light) with a wavelength
longer than the peak wavelength of light emitted by the
light-emitting element 1. Therefore, the nitridosilicate-based
phosphor 2 is excited by the light-emitting element 1, and the
semiconductor light-emitting element emits light containing at
least an emission component emitted by the nitridosilicate-based
phosphor 2.
[0085] Thus, for example, when a light-emitting apparatus is
produced with the following combination configurations, light
emitted by the light-emitting element 1 is mixed with light emitted
by the phosphor layer 3 to obtain white-based light, resulting in a
light source emitting white-based light in high demand.
[0086] (1) Configuration in which a light-emitting element that
emits near-ultraviolet light, a blue phosphor, a green phosphor,
and a red phosphor.
[0087] (2) Configuration in which a light-emitting element that
emits near-ultraviolet light, a blue phosphor, a green phosphor, a
yellow phosphor, and a red phosphor.
[0088] (3) Configuration in which a light-emitting element that
emits near-ultraviolet light, a blue phosphor, a yellow phosphor,
and a red phosphor.
[0089] (4) Configuration in which a light-emitting element that
emits blue light, a green phosphor, a yellow phosphor, and a red
phosphor.
[0090] (5) Configuration in which a light-emitting element that
emits blue light, a yellow phosphor, and a red phosphor.
[0091] (6) Configuration in which a light-emitting element that
emits blue light, a green phosphor, and a red phosphor.
[0092] (7) Configuration in which a light-emitting element that
emits blue-green light, and a red phosphor.
[0093] A nitridosilicate-based phosphor emitting red light, such as
Sr.sub.2Si.sub.5N.sub.8:Eu.sup.2+ and CaSiN.sub.2:Eu.sup.2+,
exhibits a high inner quantum efficiency under blue light
excitation. Thus, when a light-emitting apparatus is configured in
the following manner: as an excitation source for such a
nitridosilicate-based phosphor, a blue light-emitting element
having an emission peak in a blue-based wavelength region of 440 nm
to less than 500 nm, preferably, 450 nm to 480 nm, is used; the
nitridosilicate-based phosphor is excited with blue-based light
emitted by the blue light-emitting element; and the apparatus emits
light containing at least a blue-based light component emitted by
the blue light-emitting element and an emission component emitted
by the nitridosilicate-based phosphor, as output light, a
high-luminous light-emitting apparatus that has a high red light
component intensity and emits warm color based light can be
configured, which is preferable.
[0094] The nitridosilicate-based phosphor also can be any phosphor
of blue, green, yellow or red depending upon the composition.
Therefore, the nitridosilicate-based phosphor can be used for at
least one of the above-mentioned blue phosphor, green phosphor,
yellow phosphor, and red phosphor.
[0095] As the above-mentioned blue phosphor, green phosphor, yellow
phosphor, and red phosphor, other than the nitridosilicate-based
phosphor, a (Ba, Sr)MgAl.sub.10O.sub.17:Eu.sup.2+ blue phosphor, a
(Sr, Ca, Ba, Mg).sub.10(PO.sub.4).sub.6Cl.sub.2:Eu.sup.2+ blue
phosphor, a (Ba, Sr).sub.2SiO.sub.4:Eu.sup.2+ green phosphor, a
BaMgAl.sub.10O.sub.17:Eu.sup.2+, Mn.sup.2+ green phosphor, a
Y.sub.2SiO.sub.5:Ce.sup.3+, Tb.sup.3+ green phosphor, a (Y,
Gd).sub.3Al.sub.5O.sub.12:Ce.sup.3+ yellow phosphor, a
Y.sub.3Al.sub.5O.sub.12:Ce.sup.3+, Pr.sup.3+ yellow phosphor, a
(Sr, Ba).sub.2SiO.sub.4:Eu.sup.2+ yellow phosphor, a
CaGa.sub.2S.sub.4:Eu.sup.2+ yellow phosphor, a CaS:Eu.sup.2+ red
phosphor, a SrS:Eu.sup.2+ red phosphor, a
La.sub.2O.sub.2S:Eu.sup.3+ red phosphor, and the like can be
used.
[0096] In the case where the above-mentioned M constituting a
nitridosilicate-based phosphor (compound) with Eu.sup.2+ ions added
thereto as an activator is Sr, a high-performance red phosphor such
as Sr.sub.2Si.sub.5N.sub.8:Eu.sup.2+ obtained, and a phosphor
preferable as a light-emitting apparatus can be provided.
[0097] Furthermore, in the case where the above-mentioned M
constituting a nitridosilicate-based phosphor (compound) with
Eu.sup.2+ ions added thereto as an activator is Ba, for example, a
high-performance green phosphor such as BaSiN.sub.2:Eu.sup.2+ is
obtained, and a phosphor preferable for a light-emitting apparatus
can be provided.
[0098] Conventionally, a red phosphor is known in which a
nitridosilicate-based compound represented by a chemical formula:
M.sub.xSi.sub.yN.sub.z (where x, y, and z are numerical values
satisfying z=2/3x+4/3y) is used as a phosphor base material, and
Eu.sup.2+ ions are contained as a luminescent center. However, a
phosphor in which a main component of M is Ba, and x=1 and y=1 is
not known. Those skilled in the art would not easily expect that
such a phosphor happens to be a green phosphor. Thus, the present
invention relates to a nitridosilicate compound represented by a
chemical formula: BaSiN.sub.2 or a nitridosilicate phosphor
represented by BaSiN.sub.2:Eu.sup.2+ and a light-emitting apparatus
using the same.
[0099] The main component of M being Ba means that a half or more
of M, preferably 80 atomic % or more of M, and more preferably all
the M is Ba.
Example 1
[0100] Hereinafter, a method for producing a
Sr.sub.2Si.sub.5N.sub.5:Eu.sup.2+ phosphor will be described as
Example 1 of a method for producing a nitridosilicate-based
compound according to the present invention.
[0101] In Example 1, the following compounds were used as phosphor
materials.
[0102] (1) 14.47 g of strontium carbonate powder (SrCO.sub.3 with a
purity of 99.9 mol %):
[0103] (2) 0.35 g of europium oxide powder (Eu.sub.2O.sub.3 with a
purity of 99.9 mol %)
[0104] (3) 12.36 g of silicon nitride powder (Si.sub.3N.sub.4 with
a purity of 99 mol %)
[0105] Furthermore, as a reducing agent (additional reducing agent)
of the above-mentioned strontium carbonate and europium oxide, the
following solid-state carbon was used.
[0106] (4) 1.20 g of carbon (graphite) powder (C with a purity of
99.9 mol %).
[0107] First, the phosphor materials and the additional reducing
agent were sufficiently mixed with an automatic mortar in the air.
The mixed powder was placed in an alumina crucible, and the
crucible was placed at a predetermined position in an atmospheric
furnace. Thereafter, for the purpose of degassing, the mixed powder
was heated in an atmosphere of mixed gas of nitrogen and hydrogen
(97 volume % of nitrogen, 3 volume % of hydrogen) at 800.degree. C.
for 5 hours, followed by provisional firing. After provisional
firing, the mixed powder was heated in an atmosphere of the
above-mentioned mixed gas of nitrogen and hydrogen at 1600.degree.
C. for 2 hours, followed by firing. For simplicity, aftertreatment
such as cracking, classification, and washing was omitted.
Comparative Example 1
[0108] For comparison, a Sr.sub.2Si.sub.5N.sub.8:Eu.sup.2+ phosphor
also was produced by a conventional production method using a
nitride of alkaline-earth metal. In production of a sample for
comparison, the following compounds were used as phosphor
materials.
[0109] (1) 25.00 g of strontium nitride powder (Sr.sub.3N.sub.2
with a purity of 99.5 mol %)
[0110] (2) 0.93 g of europium oxide powder (Eu.sub.2O.sub.3 with a
purity of 99.9 mol %)
[0111] (3) 32.51 g of silicon nitride powder (Si.sub.3N.sub.4 with
a purity of 99 mol %)
[0112] In production of the sample for comparison, carbon powder
was not used as an additional reducing agent. The sample for
comparison was produced by the same method and under the same
conditions as those of the method for producing a
Sr.sub.2Si.sub.5N.sub.8:Eu.sup.2+ phosphor of Example 1, except
that strontium nitride powder was weighed in an atmosphere of
nitrogen with a glove box, and the phosphor materials were manually
mixed sufficiently in an atmosphere of nitrogen.
[0113] Hereinafter, the characteristics of fired materials
(Sr.sub.2Si.sub.5N.sub.8:Eu.sup.2+ phosphors) obtained by the
above-mentioned production methods will be described.
[0114] The body color of the fired materials were vivid orange.
FIG. 2 shows an X-ray diffraction pattern of the fired material of
Example 1 obtained by the above-mentioned production method. FIG. 2
shows that a main component of the fired material is a
Sr.sub.2Si.sub.5N.sub.8 compound.
[0115] FIG. 3 shows emission spectra of the fired materials of
Example 1 and Comparative Example 1 under ultraviolet excitation of
254 nm. FIG. 3 shows that the fired materials are red phosphors
having an emission peak in the vicinity of a wavelength of 633 nm.
Furthermore, the height of the emission peak (emission intensity)
of the red phosphor of Example 1 was 107% assuming that the
emission intensity of the phosphor of Comparative Example 1 was
100%. Thus, the phosphor of Example 1 had higher brightness than
that of the Sr.sub.2Si.sub.5N.sub.8:Eu.sup.2+ produced by the
conventional production method. The chromaticity (x, y) of light
emission on CIE chromaticity coordinates was x=0.605 and
y=0.380.
[0116] Furthermore, the constituent elements of the above-mentioned
fired materials were evaluated with an X-ray microanalyzer (XMA),
revealing that the fired materials were compounds mainly containing
Sr, Eu, Si, and N. Furthermore, a small amount of oxygen (O) was
detected from the fired material of Comparative Example 1, whereas
O was not substantially detected from the fired material of Example
1. The atomic ratio of metal elements constituting the fired
material of Example 1 was close to Sr:Eu:Si=1.96:0.04:5.0
[0117] These results show that a
(Sr.sub.0.98Eu.sub.0.02).sub.2Si.sub.5N.sub.8 compound, i.e., a
Sr.sub.2Si.sub.5N.sub.8:Eu.sup.2+ phosphor was produced by the
production method of Example 1.
[0118] In Example 1, it is considered based on the following
Chemical Formula 1 that SrO of an alkaline-earth metal oxide
reacted with nitrogen and silicon nitride while being reduced with
carbon (C) together with EuO of a lanthanide oxide, whereby a
(Sr.sub.0.98Eu.sub.0.02).sub.2Si.sub.5N.sub.8 compound was
generated.
5.88SrCO.sub.3+0.06Eu.sub.2O.sub.3+5Si.sub.3N.sub.4+6C+2N.sub.2+0.06H.su-
b.23.fwdarw.(Sr.sub.0.98Eu.sub.0.02).sub.2Si.sub.5N.sub.8+5.88CO.sub.2.upa-
rw.+6CO.uparw.+0.06H.sub.2O.uparw. Chemical Formula 1
[0119] Thus, according to the production method of Example 1, a
nitridosilicate-based compound was produced using, as a supply
source of alkaline-earth metal, strontium carbonate that is easy to
handle and inexpensive, without using Sr metal and Sr.sub.3N.sub.2
that are chemically unstable, are difficult to handle in the air,
and are expensive.
[0120] In Example 1, the nitridosilicate-based compound mainly
containing Sr as alkaline-earth metal and containing Eu.sup.2+ ions
as a luminescent center has been described. A nitridosilicate-based
compound mainly containing alkaline-earth metal (e.g., Ca and Ba)
other than Sr, and a nitridosilicate-based compound containing
luminescent center ions (e.g., Ce.sup.3+ ions) other than Eu.sup.2+
ions also can be produced by the same production method.
Example 2
[0121] Hereinafter, a method for producing a
Eu.sub.2Si.sub.5N.sub.8 compound will be described as Example 2 of
a method for producing a nitridosilicate-based compound according
to the present invention.
[0122] The Eu.sub.2Si.sub.5N.sub.8 compound was produced by the
same production method and under the same firing condition as those
of Example 1, except that the following materials were used as
compound materials and an additional reducing agent.
[0123] (1) 7.04 g of europium oxide powder (Eu.sub.2O.sub.3 with a
purity of 99.9 mol %)
[0124] (2) 4.94 g of silicon nitride powder (Si.sub.3N.sub.4 with a
purity of 99 mol %)
[0125] (3) 0.48 g of carbon (graphite) powder (C with a purity of
99.9 mol %)
[0126] Hereinafter, the characteristics of a fired material
(Eu.sub.2Si.sub.5N.sub.8 compound) obtained by the above-mentioned
production method will be described.
[0127] The body color of the fired material was deep red. FIG. 4
shows an X-ray diffraction pattern of the fired material obtained
by the above-mentioned production method. FIG. 4 shows that a main
component of the fired material is a Eu.sub.2Si.sub.5N.sub.8
compound. Furthermore, although the data on an emission spectrum
was omitted, the fired material had an emission peak in the
vicinity of a wavelength of 720 nm by excitation of
ultraviolet--near-ultraviolet--blue light, and exhibited light
emission of deep red with a large spectrum half-value width of
about 150 nm. The evaluation result of the constituent elements by
XMA shows that the fired material is a compound containing Eu, Si,
and N as main components, and the rough atomic ratio of the metal
elements is Eu:Si=2:5. These results show that the
Eu.sub.2Si.sub.5N.sub.8 compound was produced by the production
method of Example 2.
[0128] In Example 2, it is considered based on the following
Chemical Formula 2 that EuO of a lanthanide oxide reacted with
nitrogen and silicon nitride while being reduced with carbon (C),
whereby a Eu.sub.2Si.sub.5N.sub.8 compound was generated.
3Eu.sub.2O.sub.3+5Si.sub.3N.sub.4+6C+2N.sub.2+3H.sub.2.fwdarw.3Eu.sub.2S-
i.sub.5N.sub.8+6CO.uparw.+3H.sub.2O.uparw. Chemical Formula 2
[0129] In Example 2, the nitridosilicate-based compound mainly
containing Eu as a rare earth element has been described.
Nitridosilicate-based compounds mainly containing rare earth
elements other than Eu also can be produced by the same production
method.
Example 3
[0130] Hereinafter, a method for producing a BaSiN.sub.2:Eu.sup.2+
phosphor will be described as Example 3 of the method for producing
a nitridosilicate-based compound according to the present
invention.
[0131] In Example 3, the following compounds were used as phosphor
materials.
[0132] (1) 19.34 g of barium carbonate powder (BaCO.sub.3 with a
purity of 99.9 mol %
[0133] (2) 0.35 g of europium oxide powder (Eu.sub.2O.sub.3 with a
purity of 99.9 mol %)
[0134] (3) 4.94 g of silicon nitride powder (Si.sub.3N.sub.4 with a
purity of 99 mol %)
[0135] Furthermore, as the reducing agent (additional reducing
agent) for the above-mentioned barium carbonate and europium oxide,
the following solid-state carbon was used.
[0136] (4) 1.20 g of carbon (graphite) powder (C with a purity of
99.9 mol %)
[0137] Using these phosphor materials and additional reducing
agent, the BaSiN.sub.2:Eu.sup.2+ phosphor was produced by the same
method and under the same condition as those of the
Sr.sub.2Si.sub.5N.sub.8:Eu.sup.2+ phosphor of Example 1.
[0138] Hereinafter, the characteristics of the fired material
(BaSiN.sub.2:Eu.sup.2+ phosphor) obtained by the above-mentioned
production method will be described.
[0139] The body color of the fired material was vivid green. FIG. 5
shows an emission spectrum A and an excitation spectrum B under
ultraviolet excitation of 254 nm of the phosphor of Example 3
obtained by the above-mentioned production method.
[0140] FIG. 5 shows that the fired material can be excited with
ultraviolet--near-ultraviolet--blue light in a wavelength of 220 to
470 nm and emits green light having an emission peak in the
vicinity of a wavelength of 510 nm.
[0141] Furthermore, the constituent elements of the fired material
were evaluated in the same way as in the phosphor of Example 1,
revealing that the fired material was a compound mainly containing
Ba, Eu, Si, and N, and the atomic ratio of the metal elements
constituting the fired material was close to
Ba:Eu:Si=0.98:0.02:1.0.
[0142] These results show that a (Ba.sub.0.98Eu.sub.0.02)SiN.sub.2
compound, i.e., a BaSiN.sub.2:Eu.sup.2+ phosphor can be produced by
the production method of Example 3.
[0143] Conventionally, although a CaSiN.sub.2:Eu.sup.2+ phosphor
emitting red light is known, those skilled in the art would not
expect that the CaSiN.sub.2:Eu.sup.2+ phosphor happens to be a
green phosphor when Ca is replaced by Ba. Furthermore, the emission
intensity (peak height) of the BaSiN.sub.2:Eu.sup.2+ phosphor also
is 10 times or more that of the CaSiN.sub.2:Eu.sup.2+ produced by
the similar procedure, and has a remarkable effect that has not
been achieved conventionally.
[0144] In Example 3, it is considered based on the following
Chemical Formula 3 that BaO of an alkaline-earth metal oxide and
EuO of a lanthanide oxide substantially reacted with nitrogen and
silicon nitride while being reduced with carbon (C), whereby a
(Ba.sub.0.98Eu.sub.0.02)SiN.sub.2 compound was generated.
2.94BaCO.sub.3+0.03Eu.sub.2O.sub.3+Si.sub.3N.sub.4+3C+N.sub.2+0.03H.sub.-
2.fwdarw.3(Ba.sub.0.98Eu.sub.0.02)SiN.sub.2+2.94CO.sub.2.uparw.+3CO.uparw.-
+0.03H.sub.2O.uparw. Chemical Formula 3
[0145] Thus, according to the production method of Example 3, a
nitridosilicate-based compound represented by a chemical formula:
(Ba.sub.0.98Eu.sub.0.02)SiN.sub.2 was produced using, as a supply
source of alkaline-earth metal, barium carbonate that is easy to
handle and inexpensive, without using Ba metal and Ba.sub.3N.sub.2
that are chemically unstable, are difficult to handle in the air,
and are expensive.
[0146] In Examples 1 to 3, the
(Sr.sub.0.98Eu.sub.0.02).sub.2Si.sub.5N.sub.8 compound, the
Eu.sub.2Si.sub.5N.sub.8 compound, the
(Ba.sub.0.98Eu.sub.0.02)SiN.sub.2 compound have been exemplified
respectively. However, the method for producing a
nitridosilicate-based compound of the present invention is
applicable to nitridosilicate-based compounds other than those
described above.
INDUSTRIAL APPLICABILITY
[0147] According to the method for producing a
nitridosilicate-based compound of the present invention, a
nitridosilicate-based compound is produced by reacting an
alkaline-earth metal compound, capable of generating an
alkaline-earth metal oxide by heating, or a rare earth compound,
capable of generating a rare earth oxide by heating, with at least
a silicon compound, while the alkaline earth metal compound or the
rare earth compound is being reduced and nitrided by the reaction
with carbon in an atmosphere of nitriding gas. Therefore, a
nitridosilicate-based compound can be produced using, as a supply
source of alkaline-earth metal or a rare earth element, an alkaline
earth metal salt or a rare earth oxide that is easy to handle and
is inexpensive, without using alkaline earth metal or a nitride of
alkaline earth metal, or rare earth metal or a rare earth nitride,
which is chemically unstable, is difficult to handle in the air,
and is expensive. Thus, the present invention can be used for an
application that requires a nitridosilicate-based compound with
satisfactory material performance and a phosphor using the same to
be produced industrially at low cost.
[0148] Furthermore, a nitridosilicate-based compound is produced by
the above-mentioned production method; therefore, the present
invention also can be applied widely to an application requiring an
inexpensive nitridosilicate-based compound of high performance, and
equipment and the like are configured using an inexpensive
nitridosilicate-based compound of high performance. Consequently,
the present invention also can be applied to an application
requiring that an inexpensive product (LED light source, etc.) of
high performance, adopting a nitridosilicate-based compound, is
provided.
* * * * *