Compositions: ceramic – Ceramic compositions – Devitrified glass-ceramics
Reexamination Certificate
1999-09-17
2001-09-11
Koslow, C. Melissa (Department: 1755)
Compositions: ceramic
Ceramic compositions
Devitrified glass-ceramics
C501S002000, C501S032000, C252S30140H, C252S30140F, C252S30160R, C252S30160S
Reexamination Certificate
active
06287993
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to long-lasting phosphorescent glasses and glass-ceramics emitting a long persistent phosphorescence upon radiation of ultraviolet ray and visible light and so on, more particularly, to long-lasting phosphorescent glasses and glass-ceramics having a long-lasting phosphorescence and being capable of providing a rich variety of colors in the emitted phosphorescence.
Fluorescence is a phenomenon that a material emits visible ray when excited by an excitation source applied from outside. A fluorescent lamp, a discharge tube and cathode ray tube (CRT) emit fluorescence. A material which emits fluorescence is called a phosphor. When light emitted by a phosphor lasts after stoppage of excitation for duration of time sufficient for the light to be perceived by the eye, i.e., about 0.1 second or longer, the light is called phosphorescence. A phosphor which has a long persistent phosphorescence lasting for several hours at room temperature is called a long-lasting phosphor or a light storage phosphor.
Known in the art of long-lasting phosphors are sulfides and oxides. ZnS:Cu is a typical sulfide type long-lasting phosphor which has been practically used for several decades. The ZnS:Cu long-lasting phosphor has the disadvantage that its after-glow lasts for a relatively short duration of time, i.e., about three hours at the longest. Further, this type of phosphor has the defect that a decomposition reaction of ZnS+H
2
O→ZnO+H
2
S takes place under the coexistence of ultraviolet ray contained in the sunlight and moisture contained in the air, making particles of the phosphor become black in color and, as a result, the after-glow characteristics significantly deteriorate within a relatively short period of time. For this reason, this type of phosphor has only limited applications such as a luminous watch and a night-time display of a location in a house.
On the other hand, there are reported, as typical oxide type long-lasting phosphors, m(Sr
1−X
Eu
X
).nAl
2
O
3
.yB
2
O
3
disclosed in Chinese Patent No. CN1053807A, Zn
1−X−Y
Mg
X
.Mn
Y
and Sr
I−X
Al
2
O
4−X
:Eu
X
,Ln
Y
disclosed in Japanese Patent Application Laid-open Publication No. Hei 8-127772, (Zn
1−X−Y
Mg
X
Mn
Y
)O.n(Ga
1−Z
Al
Z
)
2
O
3
disclosed in Japanese Patent Application Laid-open Publication No. Hei 10-88126, and m(Sr
1−a
M
1
a
)O.n(Mg
1−b
M
2
b
)O.2(Si
1−c
Ge
c
)O
2
: Eu
x
,Ln
y
disclosed in Japanese Patent Application Laid-open Publication No. Hei 9-194833. These long-lasting phosphors have high phosphorescence brightness and long lasting phosphorescence and also have good chemical durability and light-proof characteristics. These long-lasting phosphors are expected to have applications which, in addition to the conventional usage for luminous watches and night-time display of a location in a house, include disaster prevention marks, position indication marks for preventing danger and decorative articles. These long-lasting phosphors, however, are all made by the sintering process which involves complex manufacturing processes and according to which it is difficult to form a product of a desired shape. Besides, in these long-lasting phosphors, it is difficult to obtain a transparent product.
It is, therefore, an object of the invention to provide long-lasting phosphorescent glasses and glass-ceramics which, while realizing high phosphorescence brightness, long lasting phosphorescence, excellent chemical durability and light-proof characteristics, can be easily manufactured and easily formed to a desired shape and which provide both transparent and opaque products as desired.
SUMMARY OF THE INVENTION
For achieving the above described object of the invention, the inventors of the present invention have conducted experiments about glasses containing SiO
2
and ZnO as their basic ingredients and found, which has led to the present invention, that a specific composition only in these glasses exhibits long-lasting phosphorescence, that phosphorescence brightness is improved and there is provided a rich variety in color of phosphorescence by adding a certain rare earth metal or Mn and that Zn
2
SiO
4
and/or ZnGa
2
O
4
crystal or crystals are formed by crystallizing these glasses whereby glass-ceramics having even better long-lasting phosphorescence characteristics can be realized.
According to the invention, there are provided long-lasting phosphorescent glasses and glass-ceramics having a composition comprising in mol %:
SiO
2
30-65%
ZnO
20-50%
Al
2
O
3
0-20%
Ga
2
O
3
0-20%
B
2
O
3
0-15%
MO
0-20%
where M is an element or elements selected from the group consisting of Mg, Ca, Sr and Ba
R
2
O
0-15%
where R is an element or elements selected from the group consisting of Li, Na and K, and
P
2
O
5
+ ZrO
2
+ SnO
2
0-8%
said composition further comprising 0-5 mol % of Ln
x
O
y
as an activator or auxiliary activator where Ln is an element or elements selected from the group consisting of Y, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Mn.
In one aspect of the invention, M in the composition is an element or elements selected from the group consisting of Ca, Sr and Ba.
In another aspect of the invention, Ln in the composition is an element or elements selected from the group consisting of Y, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Mn and, in case Eu or Dy is added, said glass or glass-ceramics contain either Eu or Dy only.
In another aspect of the invention, Ln is Tb and/or Mn.
In another aspect of the invention, the glass or glass-ceramics comprise Zn
2
SiO
4
and/or ZnGa
2
O
4
crystal phase or phases.
In comparison to ceramics which are made by sintering, glass-ceramics have the following five advantages:
(1) No troublesome mixing of raw materials is required.
(2) By stirring during melting of raw materials to glass, a very homogeneous product can be obtained and hence irregularity in the product can be avoided.
(3) A desire shape can be realized easily by utilizing the features of glass.
(4) A transparent product can be obtained by controlling conditions of heat treatment.
(5) In a case where powder is required, glass-ceramics can be easily crushed to powder since the temperature of final heat treatment is relatively low.
For these reasons, if long-lasting phosphorescent glass-ceramics are realized, improvement in the physical properties and wide applications utilizing the above described advantages of glass-ceramics over ceramics can be expected for such long-lasting phosphorescent glass-ceramics.
The inventors of the present invention have conducted experiments about glasses having SiO
2
and alkaline earth metal oxides as its basic ingredients and being added with a rare earth metal element and found that, by heat treating glass having a specific composition, long-lasting phosphorescent glass-ceramics can be obtained which exhibit long-lasting phosphorescence, high brightness and rich variety in color of the phosphorescence. Further, the inventors have found that long-lasting phosphorescent glass-ceramics obtained by mixing a base glass of these glass-ceramics with other specific materials and sintering the mixture have significantly improved lasting phosphorescence characteristics over the prior art long-lasting phosphors made of ceramics which are made by the sintering process.
Long-lasting phosphorescent glass-ceramics in this aspect of the invention have a composition in mol % of:
SiO
2
30-70%
GeO
2
0-10%
MgO
5-40%
MO
10-55%
where M is an element or elements selected from the group consisting of Ca, Sr and Ba
B
2
O
3
0-15%
Y
2
O
3
0-10%
Sc
2
O
3
0-10%
Al
2
O
3
0-10%
Ga
2
O
3
0-15%
MeO
0-10%
where Me is an element or elements selected from the group consisting of Be, Zn, Cd and Pb
R
2
O
0-6%
where R is an element or elements selected from the group consisting of Li, Na and K
Cl + F
0-8%
Bi
2
O
3
0-8%
P
2
O
5
+ ZrO
2
+ SnO
2
0-6% and
Sb
2
O
3
+ As
2
O
3
0-4%,
said composition further comprising in
Fu Jie
Ochi Yasuo
Uehara Susumu
Hedman & Costigan PC
Kabushiki Kaisha Ohara
Koslow C. Melissa
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