U.S. patent application number 14/674350 was filed with the patent office on 2015-07-23 for long-lasting phosphor ceramics and manufacturing method thereof.
This patent application is currently assigned to SHIN--ETSU CHEMICAL CO., LTD.. The applicant listed for this patent is SHIN-ETSU CHEMICAL CO., LTD.. Invention is credited to Hirofumi Kawazoe, Yuji Kimura, Yasushi Takai.
Application Number | 20150203750 14/674350 |
Document ID | / |
Family ID | 42665630 |
Filed Date | 2015-07-23 |
United States Patent
Application |
20150203750 |
Kind Code |
A1 |
Kimura; Yuji ; et
al. |
July 23, 2015 |
LONG-LASTING PHOSPHOR CERAMICS AND MANUFACTURING METHOD THEREOF
Abstract
A method for manufacturing MAl.sub.2O.sub.4:Eu,RE type
long-lasting phosphor ceramics that is capable of producing the
ceramics at a reduced raw material cost. In addition, a sintered
product of a long-lasting phosphor having no yellow body color.
More specifically, the method for manufacturing
MAl.sub.2O.sub.4:Eu,RE type long-lasting phosphor ceramics in which
M is an alkaline earth element and RE is a rare earth element other
than europium, involving mixing a BAM (alkaline earth aluminate)
phosphor, an alkaline earth compound, an aluminum compound and a
rare earth compound to form a mixture, and then firing the mixture;
and a white MAl.sub.2O.sub.4:Eu,RE type long-lasting phosphor
resulting from the method.
Inventors: |
Kimura; Yuji; (Tokyo,
JP) ; Takai; Yasushi; (Tokyo, JP) ; Kawazoe;
Hirofumi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SHIN-ETSU CHEMICAL CO., LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
SHIN--ETSU CHEMICAL CO.,
LTD.
Tokyo
JP
|
Family ID: |
42665630 |
Appl. No.: |
14/674350 |
Filed: |
March 31, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13147933 |
Aug 4, 2011 |
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PCT/JP2010/053037 |
Feb 26, 2010 |
|
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14674350 |
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Current U.S.
Class: |
252/301.4R |
Current CPC
Class: |
C04B 35/44 20130101;
C09K 11/7792 20130101; C04B 2235/3222 20130101; C04B 2235/3206
20130101; C04B 2235/3409 20130101; C04B 2235/3208 20130101; C04B
2235/763 20130101; C04B 35/62685 20130101; C04B 2235/3224 20130101;
C04B 2235/5436 20130101; C04B 35/6268 20130101; C04B 2235/604
20130101; Y02W 30/50 20150501; C04B 2235/3213 20130101; Y02W 30/72
20150501; C04B 2235/3215 20130101; C04B 2235/3262 20130101; C09K
11/01 20130101 |
International
Class: |
C09K 11/77 20060101
C09K011/77 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 2009 |
JP |
2009-045944 |
Claims
1. Long-lasting phosphor ceramics obtained by the method according
claim 1, comprising the steps of: mixing an alkaline earth
aluminate phosphor, an alkaline earth compound, an aluminum
compound, and a rare earth compound to form a mixture; and firing
the mixture, and being represented by the compositional formula
(1): M.sub.(1-r-t)Al.sub.2O.sub.4:Eu.sub.r,RE.sub.s,Mn.sub.t (1)
wherein M is at least one element selected from the group
consisting of Ba, Sr, Mg and Ca; RE is at least one rare earth
element other than Eu; r is a number from 0.005 to 0.05; s is a
number from 0.005 to 0.05; and t is a number from 0 to 0.08.
2. The long-lasting phosphor ceramics according to claim 1, having
a whiteness of L*.gtoreq.80, -10.ltoreq.a*.ltoreq.10 and
-10.ltoreq.b*.ltoreq.10, as evaluated in an L*a*b* color
system.
3. The long-lasting phosphor ceramics according to claim 1, being
represented by the compositional formula (2):
M.sub.(1-r-t)Al.sub.2O.sub.4:Eu.sub.r,Dy.sub.s,Mn.sub.t (2) wherein
M is at least one element selected from the group consisting of Ba,
Sr, Mg, and Ca; r is a number from 0.005 to 0.05; s is a number
from 0.005 to 0.05; and t is a number from 0 to 0.08; and having a
whiteness of L*.gtoreq.80, -10.ltoreq.a*.ltoreq.10 and
-10.ltoreq.b*.ltoreq.10, as evaluated in an L*a*b* color system.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a division of commonly owned, co-pending
U.S. patent application Ser. No. 13/147,933, filed Aug. 4, 2011,
which is a .sctn.371 of PCT/JP2010/053037 filed Feb. 26, 2010.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an inexpensive
manufacturing method of long-lasting phosphor ceramics to be used
in escape route signs and the like, and a sintered long-lasting
phosphor having a light body color obtainable by the above
manufacturing method.
[0004] 2. Description of Related Art
[0005] The demand for a long-lasting phosphor to be used in escape
route signs and the like has been increasing as its applications
expand, since an MAl.sub.2O.sub.4:Eu,RE type long-lasting phosphor
in which M is an alkaline earth element and RE is a rare earth
element other than Eu was discovered by Nemoto & Co., Ltd. in
1993 (see, for example, Patent Document 1 indicated below).
However, because of expensive materials and relatively high
production cost, products of the phosphor are expensive, and
accordingly, wide spread use of the phosphor has not yet been
realized sufficiently. In addition, the phosphor is accompanied
with another problem that due to a yellowish body color, it cannot
be readily applied to signs required to have a white background.
[0006] Patent Document 1: Japanese Patent No. 2543825
SUMMARY OF THE INVENTION
Problem to be Solved by the Invention
[0007] For the production of MAl.sub.2O.sub.4:Eu,RE type
long-lasting phosphors, europium, which is an expensive rare earth
element, is used as a raw material. In addition, expensive and
high-purity fine-particle type aluminum oxide, alkaline earth
carbonate, rare earth oxide and the like are necessary for
obtaining phosphors having a uniform composition. Thus, the cost of
raw material is high, and it is difficult to produce inexpensive
phosphor products. In addition, since the conventional products
have a yellowish body color, application of the products is limited
in terms of design.
[0008] With the foregoing in view, an object of the present
invention is to provide a method for manufacturing white
MAl.sub.2O.sub.4:Eu,RE type long-lasting phosphor ceramics capable
of manufacturing the ceramics at a reduced raw material cost.
Means for Solving the Problems
[0009] With a view to overcoming the problems described above, the
inventors have taken an advantage of the fact that recycling wastes
(as used herein, "recycling waste" is a waste generated during
recycling) of BAM phosphors which have been used as blue-emitting
(or green-emitting) phosphors of fluorescent lamps, plasma
television displays, liquid-crystal backlights or the like, contain
an alkaline earth aluminate base material with high alumina content
and contain an abundant amount of europium. The inventors have also
found that a long-lasting phosphor can be manufactured by mixing
the recycling waste of BAM phosphor with an alkaline earth
compound, an aluminum compound and a rare earth compound to form a
mixture, and then firing the mixture, and in addition, the
long-lasting phosphor having a white body color can be obtained
thereby. Consequently, the inventors have reached the present
invention. The mechanism of the resulting long-lasting phosphor
providing a white body color has not yet been elucidated. Although
such a mechanism does not limit the technical scope of the present
invention, it is assumed to involve that use of a Eu raw material
which has already been dispersed uniformly in BAM can prevent Eu in
the long-lasting phosphor from being unevenly distributed therein.
Compounds having only divalent Eu such as EuCO.sub.3 are likely to
provide a yellowish body color so that uneven distribution of the
Eu component may cause such a yellowish body color.
[0010] The present invention relates to a low-cost manufacturing
method of long-lasting phosphor ceramics, comprising the steps of
mixing a BAM phosphor with an alkaline earth compound, an aluminum
compound and a rare earth compound to form a mixture, and firing
the resulting mixture; and white long-lasting phosphor ceramics
obtainable by this method.
Effect of the Invention
[0011] According to the present invention, long-lasting phosphor
ceramics can be manufactured at a very low cost without using
expensive europium as a raw material, by mixing a BAM phosphor
contained in phosphor wastes with an alkaline earth compound, an
aluminum compound and a rare earth compound, and by firing the
resulting mixture. In addition, the obtained long-lasting phosphor
ceramics has a white body color. By synergistic effects of these
advantages, it is expected to increase the application fields of
long-lasting phosphor ceramics so that this method is of great
value.
DETAILED DESCRIPTION OF THE INVENTION
[0012] Hereinafter, the present invention will be described more
specifically.
<Composition of Raw Materials>
[0013] An alkaline earth aluminate (BAM) phosphor used as a raw
material in the present invention is represented by:
p(M1.sub.1-xEu.sub.x)O.(M2.sub.1-yMn.sub.y)O.qAl.sub.2O.sub.3
wherein M1 is at least one element selected from the group
consisting of Ba, Sr, and Ca, and preferably Ba; M2 is Mg; and p,
q, x and y are numbers which satisfy the following:
0.8.ltoreq.p.ltoreq.1.2, 4.5.ltoreq.q.ltoreq.835,
0.05.ltoreq.x.ltoreq.0.3, and 0.ltoreq.y.ltoreq.0.4,
respectively.
[0014] Each element of the alkaline earth aluminate phosphor can be
determined by X-ray fluorescence (XRF) analysis.
[0015] The term "alkaline earth compound" as used herein indicates
a compound having one or more elements selected from the group
consisting of Mg, Ca, Sr and Ba and being converted into an oxide
in a firing step described later, or indicates a compound having an
oxide itself of one or more elements selected therefrom.
[0016] The term "rare earth compound" as used herein indicates a
compound having one or more elements selected from the group
consisting of La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, T, Yb, Lu, Y
and Sc and being converted into an oxide in a firing step described
later, or indicates a compound having an oxide itself of one or
more elements selected therefrom.
[0017] The term "aluminum compound" as used herein indicates a
compound which will be converted into an oxide thereof in the
firing step described later, or indicates an oxide compound
itself.
[0018] The BAM phosphor used herein preferably includes: the
recycling wastes of BAM phosphors which were used as blue-emitting
or green-emitting phosphors in fluorescent lamps, plasma television
displays, liquid-crystal display backlights and the like; the
wastes generated during applying and/or washing processes of BAM
phosphors; or BAM phosphors which fail to meet characteristics
and/or specifications generally required in the art.
[0019] The BAM phosphor to be used in the present invention can be
obtained from, in most cases, a waste mixture with the other
phosphor or phosphors such as Y.sub.2O.sub.3:Eu (red) and
LaPO.sub.4:CeTb (green). The phosphor or phosphors other than BAM
are dissolved by a treatment such as acid decomposition and each
element therein is recycled in a process already established.
Although JP 2004-262978 A proposes a method for recovering BAM
phosphors having a markedly low solubility, the phosphors undergo
significant deterioration in brightness during their recovering
steps. Accordingly, this method has not yet been put into practical
use and the BAM phosphors are not reused but discarded as a
residue, currently.
[0020] The BAM phosphor residue separated and recovered from the
recycling waste of phosphors can be regarded as a cost-free raw
material.
[0021] The manufacturing method of the present invention comprises
a mixing step of raw materials and a firing step of the resulting
mixture.
[0022] First, in the mixing step, powder mixing of a BAM phosphor,
an alkaline earth compound, an aluminum compound and a rare earth
compound in a ball mill or the like can be selected.
[0023] Raw material powders used for the powder mixing have
preferably an average particle size of from 0.3 to 50 .mu.m as
measured using an FRA measuring instrument (Micro-trak Systems)
with a laser diffraction/scattering method as a measuring
principle. When the average particle size is less than 0.3 .mu.m,
powders may not be dispersed uniformly in the mixing step because
of firm agglomeration of the powders. An obtained phosphor may be a
phosphor with a poor long-lasting brightness. When the average
particle size exceeds 50 .mu.m, the reaction between raw material
powders may not proceed sufficiently and a obtained phosphor may be
a phosphor with a poor long-lasting brightness.
[0024] As the alkaline earth compound or rare earth compound, any
compounds can be used insofar as they may become an oxide through a
below-mentioned firing step. Examples include carbonates, oxides,
hydroxides, and acetates.
[0025] As the aluminum compound, any compounds can be used insofar
as they may become an oxide through the below-mentioned firing
step. Examples include oxides, hydroxides, and acetates.
[0026] The alkaline earth compound and the aluminum compound are
added preferably in an amount to give a final composition of
MAl.sub.2O.sub.4, which is an amount to give a mole ratio of the
sum of alkaline earth metal elements to aluminum of 1:2. Lasting
brightness can, however, be observed even if there is some degree
of difference in the composition.
[0027] The alkaline earth compound, the aluminum compound, and the
rare earth compound are added, for example, in an amount of from 3
to 35 mol, from 0 to 65 mol, and from 0 to 1 mol (in terms of an
amount of each element by mole), respectively, per mol of the BAM
phosphor (represented by the above composition formula) to give a
composition of MAl.sub.2O.sub.4:Eu,RE,(Mn).
[0028] Addition of a small amount (for example, 10 mol % or less of
the total amount of the alkaline earth elements) of a compound,
which will become boron oxide through the below-mentioned firing
step, such as boric acid or boron oxide, as a flux during mixing of
the raw materials, facilitates the progress of the reaction and
improves long-lasting brightness.
[0029] The firing step is performed under a reducing atmosphere
(for example, under mixed gas atmosphere of nitrogen and hydrogen)
or inert gas atmosphere (for example, nitrogen or argon atmosphere)
(at from 1000 to 1500.degree. C.). This is because firing under an
oxidizing atmosphere such as air may oxidize a part of divalent Eu,
which is an emission center, into trivalent Eu and deteriorate the
long-lasting brightness.
[0030] The manufacturing method of the long-lasting phosphor
ceramics of the present invention can produce particles having an
average particle size of from 1 .mu.m to 1000 .mu.m by grinding
after the firing step, or a sintered long-lasting phosphor by
molding a mixture of the raw materials into a desired form and then
firing.
[0031] The obtained long-lasting phosphor of the present invention
has a white appearance, though a long-lasting phosphor manufactured
through a conventional method without a BAM raw material has a
yellowish body color. This difference is particularly marked in a
light storage phosphor having a composition range represented by
the following formula (1):
M.sub.(1-r-t)Al.sub.2O.sub.4:Eu.sub.r,RE.sub.s,Mn.sub.t (1)
wherein M is at least one element selected from the group
consisting of Ba, Sr, Mg and Ca; RE is at least one rare earth
element other than Eu; r is a number from 0.005 to 0.05; s is a
number from 0.005 to 0.05; and t is a number from 0 to 0.08; or in
a light storage phosphor having a composition range represented by
the following formula (2):
M.sub.(1-r-t)Al.sub.2O.sub.4:Eu.sub.r,Dy.sub.s,Mn.sub.t (2)
wherein M is at least one element selected from the group
consisting of Ba, Sr, Mg and Ca; r is a number from 0.005 to 0.05;
s is a number from 0.005 to 0.05; and t is a number from 0 to
0.08.
[0032] It is particularly marked in a light storage phosphor having
a composition range represented by M.sub.(1-r)Al.sub.2O.sub.4:
Eu.sub.r,Dy.sub.s, wherein 0.005.ltoreq.r.ltoreq.0.05 and
0.005.ltoreq.s.ltoreq.0.05.
[0033] The long-lasting brightness characteristic of the light
storage phosphor according to the present invention was evaluated
in the following manner: expose its sample to a D65 standard light
of 2400 Lx for 10 minutes; measure long-lasting brightness of the
sample by using a luminance meter (LS-110, Konica Minolta Sensing,
Inc.) 60 minutes after blocking of an excited light; and evaluate
the long-lasting brightness with a value relative to the brightness
of a commercially available ZnS:Cu long-lasting phosphor powder
(Product No. GSS, Nemoto & Co., Ltd.) set at 1.0.
[0034] The whiteness used herein is defined by the CIE1976 L*a*b*
color system established by CIE (International Commission on
Illumination) in 1976. The above-described composition has a
whiteness of L*.gtoreq.80, -10.ltoreq.a*.ltoreq.10, and
-10.ltoreq.b*.ltoreq.10.
[0035] To measure the whiteness by using the L*a*b* color system, a
colorimeter (CR200, Minolta) was used.
[0036] Both the long-lasting brightness and whiteness were measured
after press-molding 5 g of a powder sample under a pressure of 100
kg/cm.sup.2 by using a mold having a diameter of 30 mm. A sintered
product obtained by press-molding of a raw material mixed powder
and then firing was subjected to the measurement as it was.
EXAMPLES
[0037] Examples of the present invention will hereinafter be
described. It should not be construed that the present invention is
limited to or by them.
Example 1
[0038] To 14.2 g (0.02 mol) of a blue-emitting BAM phosphor
(Ba.sub.0.9MgAl.sub.10O.sub.17:Eu.sub.0.1) (determined by XRF X-ray
fluorescence analysis) having an average particle size of 7.5 .mu.m
and recovered from waste lamps, added were 23.9 g (0.16 mol) of
strontium carbonate having an average particle size of 2.2 .mu.m,
10.3 g (0.1 mol) of aluminum oxide having an average particle size
of 3.5 .mu.m, 0.94 g (0.0025 mol) of dysprosium oxide having an
average particle size of 7.3 .mu.m, and 1 g of boric acid which
have passed through 200 mesh, followed by mixing in a ball mill.
The resulting mixture was fired at 1300.degree. C. for one hour
(under 97:3 nitrogen-hydrogen atmosphere) in an alumina crucible to
obtain a long-lasting phosphor.
[0039] The obtained phosphor had a composition of
Sr.sub.0.800Ba.sub.0.090Mg.sub.0.100Al.sub.2O.sub.4:
Eu.sub.0.010,Dy.sub.0.025 and had a good long-lasting brightness as
high as 18.5. In addition, it had a whiteness of L*=92.0, a*=-4.3
and b*=6.5, and thus had a white appearance.
Examples 2 to 4
[0040] In the same manner as in Example 1 except for the
compositions, long-lasting phosphors were obtained.
[0041] Details of the mixed raw materials in respective examples
are shown in Table 2, while the compositions and results of color
evaluation are shown in Table 2.
Example 5
[0042] In the same manner as in Example 1, a raw material mixed
powder was prepared. Prior to firing, 5 g of the resulting mixed
powder was press-molded under a pressure of 100 kg/cm.sup.2 by
using a mold having a diameter of 30 mm, and fired under the same
conditions as those in Example 1 to obtain a sintered product of a
long-lasting phosphor. The obtained sintered product had a good
long-lasting brightness as high as 33.8. It had a whiteness of
L*=93.5, a*=-4.1 and b*=5.6, and thus had a white appearance.
Example 6
[0043] To 14.5 g (0.02 mol) of a green-emitting BAM phosphor
(Ba.sub.0.85Mg.sub.0.7Al.sub.10O.sub.17: Eu.sub.0.15,Mn.sub.0.3)
(determined by XRF X-ray fluorescence analysis) having an average
particle size of 8.1 .mu.m and recovered from waste lamps, added
were 24.0 g (0.16 mol) of strontium carbonate, 10.4 g (0.1 mol) of
aluminum oxide, 0.95 g (0.13 mol) of dysprosium oxide, and 1 g of
boric acid, followed by mixing in a ball mill. Prior to firing, 5 g
of the resulting mixture was press-molded under a pressure of 100
kg/cm.sup.2 by using a mold having a diameter of 30 mm. The
press-molded mixture was then fired at 1300.degree. C. for one hour
(under 97:3 nitrogen-hydrogen atmosphere) in an alumina crucible to
obtain a sintered product of a long-lasting phosphor. The obtained
long-lasting phosphor had a composition of
Sr.sub.0.800Ba.sub.0.085Mg.sub.0.070Al.sub.2O.sub.4:Eu.sub.0.015,
Mn.sub.0.030,Dy.sub.0.025 and had a good long-lasting brightness as
high as 31.0. In addition, it had a whiteness of L*=93.1, a*=-4.5
and b*=6.4, and thus had a white appearance.
Example 7
[0044] To 14.2 g (0.02 mol) of a blue-emitting BAM phosphor
(Ba.sub.0.9MgAl.sub.10O.sub.17:Eu.sub.0.1) recovered from waste
lamps, added were 16.2 g (0.162 mol) of calcium carbonate having an
average particle size of 2.8 .mu.m, 10.3 g (0.1 mol) of aluminum
oxide, 0.33 g (0.001 mol) of lanthanum oxide having an average
particle size of 6.6 .mu.m, 0.34 g (0.001 mol) of neodymium oxide
having an average particle size of 7.4 .mu.m, and 1 g of boric
acid, followed by mixing in a ball mill. The resulting mixture was
then fired at 1300.degree. C. for one hour (under 97:3
nitrogen-hydrogen atmosphere) in an alumina crucible to obtain a
long-lasting phosphor.
[0045] The obtained phosphor had a composition of
Ca.sub.0.800Ba.sub.0.090Mg.sub.0.100Al.sub.2O.sub.4:Eu.sub.0.010,
La.sub.0.010,Nd.sub.0.010 and had a good long-lasting brightness as
high as 5.6. In addition, it had a whiteness of L*=94.1, a*=-3.0
and b*=2.4, and thus had a white appearance.
Example 8
[0046] To 14.2 g (0.02 mol) of a commercially-available
blue-emitting BAM phosphor (Nichia Corporation, average particle
size: 8.3 .mu.m, Ba.sub.0.9MgAl.sub.10O.sub.17:Eu.sub.0.1
determined by XRF X-ray fluorescence analysis), added were 23.9 g
(0.16 mol) of strontium carbonate having an average particle size
of 2.2 .mu.m, 10.3 g (0.1 mol) of aluminum oxide having an average
particle size of 3.5 .mu.m, 0.94 g (0.0025 mol) of dysprosium oxide
having an average particle size of 7.3 .mu.m, and 1 g of boric acid
which has passed through 200 mesh, followed by mixing in a ball
mill. The resulting mixture was then fired at 1300.degree. C. for
one hour (under 97:3 nitrogen-hydrogen atmosphere) in an alumina
crucible to obtain a long-lasting phosphor.
[0047] The obtained phosphor had a composition of
Sr.sub.0.800Ba.sub.0.090Mg.sub.0.100Al.sub.2O.sub.4:Eu.sub.0.010,
Dy.sub.0.025 and had a good long-lasting brightness as high as
19.8. In addition, it had a whiteness of L*=93.2, a*=-4.1 and
b*=6.1, and thus had a white appearance.
Comparative Example 1
[0048] The 3.6 g of barium carbonate having an average particle
size of 2.4 .mu.m, 1.7 g of magnesium carbonate having an average
particle size of 3.2 .mu.m, 23.9 g of strontium carbonate, 20.6 g
of aluminum oxide, 0.36 g of europium oxide having an average
particle size of 6.7 .mu.m, 0.94 g of dysprosium oxide, and 1 g of
boric acid were separately added, followed by mixing in a ball
mill. The resulting mixture was then fired at 1300.degree. C. for
one hour (under 97:3 nitrogen-hydrogen atmosphere) in an alumina
crucible to obtain a long-lasting phosphor. The obtained phosphor
had a composition of
Sr.sub.0.800Ba.sub.0.090Mg.sub.0.100Al.sub.2O.sub.4:Eu.sub.0.010,Dy.sub.0-
.025 and had a good long-lasting brightness as high as 20.1. It had
however a whiteness of L*=88.1, a*=-10.2 and b*=19.6, and thus had
a yellowish body color.
Comparative Example 2
[0049] In the same manner as in Comparative Example 1 except for
the composition, a long-lasting phosphor was obtained.
[0050] The details of the mixed raw materials are shown in Table 1,
while the composition and the color evaluation results are shown in
Table 2.
Comparative Example 3
[0051] A sintered product of a long-lasting phosphor was obtained
by preparing a raw material mixed powder in the same manner as in
Comparative Example 1, press-molding of 5 g of the resulting mixed
powder under a pressure of 100 kg/cm.sup.2 in a mold having a
diameter of 30 mm, and then firing under the same conditions as
those in Comparative Example 1. The obtained phosphor had a good
long-lasting brightness as high as 33.3. It had however a whiteness
of L*=90.3, a*=-8.7 and b*=16.9, and thus had a yellowish body
color.
Comparative Example 4
[0052] The 29.5 g of strontium carbonate, 20.6 g of aluminum oxide,
0.36 g of europium oxide, 0.94 g of dysprosium oxide, and 1 g of
boric acid were separately added, followed by mixing in a ball
mill. The resulting mixture was then fired at 1300.degree. C. for
one hour (under 97:3 nitrogen-hydrogen atmosphere) in an alumina
crucible to obtain a long-lasting phosphor. The obtained phosphor
had a composition of
Sr.sub.0.990Al.sub.2O.sub.4:Eu.sub.0.010,Dy.sub.0.025 and had a
good long-lasting brightness as high as 20.3. It had however a
whiteness of L*=87.9, a*=-9.3 and b*=19.2, and thus had a yellowish
body color.
TABLE-US-00001 TABLE 1 Aluminum BAM phosphor Alkaline earth
compound compound Rare earth compound Blue- Green- mole ratio mole
ratio mole ratio Boric emitting emitting BAM amount relative to
Al.sub.2O.sub.3 relative to amount relative to acid BAM (g) BAM (g)
(mol) kind (g) BAM (g) BAM kind (g) BAM (g) Example 1 14.2 -- 0.020
SrCO.sub.3 23.9 8.1 10.3 5 Dy.sub.2O.sub.3 0.94 0.13 1 Example 2
26.1 -- 0.037 SrCO.sub.3 19.1 3.5 1.9 0.5 Dy.sub.2O.sub.3 1.73 0.13
1 Example 3 4.3 -- 0.006 SrCO.sub.3 27.8 31.4 17.4 28.4
Dy.sub.2O.sub.3 0.28 0.13 1 Example 4 10.1 -- 0.014 SrCO.sub.3 25.5
12.3 13.2 9.2 Dy.sub.2O.sub.3 0.67 0.13 1 Example 5 14.2 -- 0.020
SrCO.sub.3 23.9 8.1 10.3 5 Dy.sub.2O.sub.3 0.94 0.13 1 Example 6 --
14.5 0.020 SrCO.sub.3 24 8.13 10.4 5.1 Dy.sub.2O.sub.3 0.95 0.13 1
Example 7 14.2 -- 0.020 CaCO.sub.3 16.2 8.1 10.3 5 La.sub.2O.sub.3
+ 0.33 + 0.1 1 Nd.sub.2O.sub.3 0.34 Example 8 14.2 -- 0.020
SrCO.sub.3 23.9 8.1 10.3 5 Dy.sub.2O.sub.3 0.94 0.13 1 Aluminum
Alkaline earth compound compound Rare earth compound Boric
BaCO.sub.3 BaCo.sub.3 MgCO.sub.3 MgCO.sub.3 SrCO.sub.3 SrCO.sub.3
Al.sub.2O.sub.3 Al.sub.2O.sub.3 added total acid (g) (mol) (g)
(mol) (g) (mol) (g) (mol) added (g) (mol) (g) Comp. Ex. 1 3.6 0.018
1.7 0.02 23.9 0.16 20.6 0.2 Eu.sub.2O.sub.3 + 0.36 + 0.00364 1
Dy.sub.2O.sub.3 0.94 Comp. Ex. 2 1.1 0.006 0.5 0.006 27.8 0.19 20.5
0.2 Eu.sub.2O.sub.3 + 0.11 + 0.00109 1 Dy.sub.2O.sub.3 0.28 Comp.
Ex. 3 3.6 0.018 1.7 0.002 23.9 0.16 20.6 0.2 Eu.sub.2O.sub.3 + 0.36
+ 0.00364 1 Dy.sub.2O.sub.3 0.94 Comp. Ex. 4 -- -- -- -- 29.5 0.2
20.6 0.2 Eu.sub.2O.sub.3 + 0.36 + 0.00364 1 Dy.sub.2O.sub.3
0.94
TABLE-US-00002 TABLE 2 Long-lasting Composition brightness L* a* b*
Appearance Ex. 1
(Sr.sub.0.800Ba.sub.0.090Mg.sub.0.100)Al.sub.2O.sub.4:Eu.sub.0.010,
Dy.sub.0.025 18.5 92 -4.3 6.5 white Ex. 2
(Sr.sub.0.636Ba.sub.0.164Mg.sub.0.182)Al.sub.2O.sub.4:Eu.sub.0.018,
Dy.sub.0.045 16.5 90 -4.8 7.8 white Ex. 3
(Sr.sub.0.939Ba.sub.0.028Mg.sub.0.030)Al.sub.2O.sub.4:Eu.sub.0.003,
Dy.sub.0.008 4.4 95.7 -3.3 3.8 white Ex. 4
(Sr.sub.0.857Ba.sub.0.065Mg.sub.0.071)Al.sub.2O.sub.4:Eu.sub.0.007,
Dy.sub.0.018 13.9 93.6 -4.3 5.3 white Ex. 5
(Sr.sub.0.800Ba.sub.0.090Mg.sub.0.100)Al.sub.2O.sub.4:Eu.sub.0.010,
Dy.sub.0.025 33.8 93.5 -4.1 5.6 white Ex. 6
(Sr.sub.0.800Ba.sub.0.085Mg.sub.0.070)Al.sub.2O.sub.4:Eu.sub.0.015,
Mn.sub.0.030, Dy.sub.0.025 31 93.1 -4.5 6.4 white Ex. 7
Ca.sub.0.800Ba.sub.0.090Mg.sub.0.100Al.sub.2O.sub.4:Eu.sub.0.010,
La.sub.0.010, Nd.sub.0.010 5.6 94.1 -3 2.4 white Ex. 8
(Sr.sub.0.800Ba.sub.0.090Mg.sub.0.100)Al.sub.2O.sub.4:Eu.sub.0.010,
Dy.sub.0.025 19.8 93.2 -4.1 6.1 white Comp. Ex. 1
(Sr.sub.0.800Ba.sub.0.090Mg.sub.0.100)Al.sub.2O.sub.4:Eu.sub.0.010,
Dy.sub.0.025 20.1 88.1 -10.2 19.6 yellow Comp. Ex. 2
(Sr.sub.0.939Ba.sub.0.027Mg.sub.0.030)Al.sub.2O.sub.4:Eu.sub.0.003,
Dy.sub.0.008 5.2 91.1 -5.9 9.7 pale yellow Comp. Ex. 3
(Sr.sub.0.800Ba.sub.0.090Mg.sub.0.100)Al.sub.2O.sub.4:Eu.sub.0.010,
Dy.sub.0.025 33.3 90.3 -8.7 16.9 yellow Comp. Ex. 4
Sr.sub.0.990Al.sub.2O.sub.4:Eu.sub.0.010, Dy.sub.0.025 20.3 87.9
-9.3 19.2 yellow
[0053] It is evident from the results shown in Tables 1 and 2 that
although the long-lasting phosphors obtained in both Example 1 and
Comparative Example 1 have the same composition and have an
aluminum compound added, the long-lasting phosphor of Example 1
using a BAM phosphor as a raw material has a higher whiteness and a
white appearance.
[0054] It is also evident that although the sintered products
obtained in Example 5 and Comparative Example 3 has the same
composition, there is a difference in whiteness between them.
[0055] It is evident that a difference in whiteness between the
long-lasting phosphors obtained in Example 5 and Comparative
Example 3 both containing Eu at a ratio of 0.05 or greater is more
remarkable than a difference in whiteness between the long-lasting
phosphors obtained in Example 3 and Comparative Example 2 both
containing Eu at a ratio less than 0.05.
[0056] It is evident from the results of Example 7 that a
long-lasting phosphor having a white appearance and a higher
whiteness can be obtained even when two rare earth compounds are
used.
[0057] It is evident from the results of Example 8 that a
long-lasting phosphor having a higher whiteness can be obtained
even when a commercially available BAM phosphor is used.
* * * * *