Compositions – Inorganic luminescent compositions – Compositions containing halogen; e.g. – halides and oxyhalides
Reexamination Certificate
2001-09-25
2004-10-12
Koslow, C. Melissa (Department: 1755)
Compositions
Inorganic luminescent compositions
Compositions containing halogen; e.g., halides and oxyhalides
C252S30160F
Reexamination Certificate
active
06802990
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to fluorescent substances, especially suitably used for vacuum ultraviolet radiation excited light-emitting devices such as plasma display panels (hereinafter referred to as “PDPs”) and rare gas lamps.
BACKGROUND OF THE INVENTION
Fluorescent substances that emit light when excited with vacuum ultraviolet radiation or the like include, for example, BaMgAl
10
O
17
:Eu comprising Ba, Mg, Al, O and an activator (Eu) as a blue fluorescent substance for vacuum ultraviolet radiation excited light-emitting devices, and Zn
2
SiO
4
:Mn comprising Zn, Si, O and an activator (Mn) as a green fluorescent substance. As well, (Y,Gd)BO
3
:Eu comprising Y, Gd, B, O and an activator (Eu), for example, has been known as a red fluorescent substance. Such fluorescent substances are also used in rare gas lamps. These prior art fluorescent substances for vacuum ultraviolet radiation excited light-emitting devices, however, are desired to exhibit further enhanced luminance.
In vacuum ultraviolet radiation excited light-emitting devices such as PDPs and rare gas lamps, causing discharge in a rare gas generates plasma and then, vacuum ultraviolet radiation is generated. The prior art fluorescent substances involve a problem that the luminance thereof decreases as they are exposed to plasma. Thus, there is a desire for a fluorescent substance for vacuum ultraviolet radiation excited light-emitting devices of which luminance does not much decrease due to exposure to plasma.
U.S. Pat. No. 5,839,718 discloses a silicate fluorescent substance comprising a compound represented by the general formula: 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
, wherein M
1
is Ba, M
2
is at least one element selected from the group consisting of Be, Zn and Cd, Ln is at least one element selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, B, Al, Ga, In, Tl, Sb, Bi, As, P, Sn, Pb, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Cr and Mn. Specific examples of such silicate fluorescent substances disclosed include Sr
1.995
MgSi
2
O
7
:Eu
0.005
, Dy
0.025
, Cl
0.025
, and Sr
0.445
Ba
1.55
MgSi
2
O
7
:Eu
0.005
, Dy
0.025
, Cl
0.025
. These fluorescent substances are for use as light accumulators for display in dark places or for similar purposes. “Extended abstracts of the sixth international conference on the science and technology of display phosphors”, pages 21-24, discloses CaMgSi
2
O
6
:Eu as a fluorescent substance for vacuum ultraviolet radiation excited light-emitting devices.
Such fluorescent substances comprising silicate still have the problem that their luminance is insufficient and decreases due to exposure to plasma.
It is an object of the present invention to provide a fluorescent substance for vacuum ultraviolet radiation excited light-emitting devices which emits light with a higher luminance and a small decrease in luminance after the exposure to plasma.
SUMMARY OF THE INVENTION
Under such circumstances, the inventors of the present invention have made an intensive and continuous study in pursuit of resolving the foregoing problems and, as a result, have found that, among silicate or germanate fluorescent substances for vacuum ultraviolet radiation excited light-emitting devices, a fluorescent substance having a specific composition comprising: a compound represented by the general formula, mM
1
O·nM
2
O·2M
3
O
2
, wherein M
1
is at least one metal selected from the group consisting of Ca, Sr and Ba, M
2
is at least one metal selected from the group consisting of Mg and Zn, M
3
is at least one metal selected from the group consisting of Si and Ge, and m and n satisfy 0.5≦m≦3.5 and 0.5≦n≦2.5, respectively, provided that when m=n=1, M
1
is either at least two metals selected from the group consisting of Ca, Sr and Ba, or one of Sr and Ba; and either one of Eu or Mn as an activator, emits light with a higher luminance and a smaller decrease in luminance after the exposure to plasma. Thus, the present invention has been completed.
Accordingly, the present invention provides a fluorescent substance for vacuum ultraviolet radiation excited light-emitting devices, comprising: a compound represented by the general formula, mM
1
O·nM
2
O·2M
3
O
2
, wherein M
1
is at least one metal selected from the group consisting of Ca, Sr and Ba, M
2
is at least one metal selected from the group consisting of Mg and Zn, M
3
is at least one metal selected from the group consisting of Si and Ge, and m and n satisfy 0.5≦m≦3.5 and 0.5≦n≦2.5, respectively, provided that when m=n=1, M
1
is either at least two metals selected from the group consisting of Ca, Sr and Ba, or one of Sr and Ba; and either one of Eu or Mn as an activator. The present invention also provides a vacuum ultraviolet radiation excited light-emitting device comprising the fluorescent substance defined above.
DETAILED DESCRIPTION OF THE INVENTION
The fluorescent substance for vacuum ultraviolet radiation excited light-emitting devices according to the present invention is characterized by comprising: a base crystal formed of a compound represented by the general formula: mM
1
O·nM
2
O·2M
3
O
2
, wherein M
1
is at least one metal selected from the group consisting of Ca, Sr and Ba, M
2
is at least one metal selected from the group consisting of Mg and Zn, M
3
is at least one metal selected from the group consisting of Si and Ge, and m and n satisfy 0.5≦m≦3.5 and 0.5≦n≦2.5, respectively, provided that when m=n=1, M
1
is either at least two metals selected from the group consisting of Ca, Sr and Ba, or one of Sr and Ba; and either one of Eu or Mn as an activator.
When m=n=1 in the above-noted general formula, M
1
is selected from the group consisting of Sr, Ba, the combination of Sr, Ba and Ca, combination of Sr and Ca, combination of Ba and Sr, and combination of Ba and Ca.
Preferably, the fluorescent substance for vacuum ultraviolet radiation excited light-emitting devices according to the present invention has a crystal structure as same as diopside, akermanite, or merwinite.
Among fluorescent substances having the same crystal structure as diopside, one comprising a compound of the above-noted general formula where m=n=1 is preferable. A more preferable one as a fluorescent substance for vacuum ultraviolet radiation excited light-emitting devices is of a composition in which M
1
is partially replaced with the activators Eu, or M
2
is partially replaced with the activators Mn, and which is represented by the general formula: (M
1
1-a
Eu
a
)M
2
M
3
2
O
6
or M
1
(M
2
1-b
Mn
b
)M
3
2
O
6
, wherein M
1
is either at least two metals selected from the group consisting of Ca, Sr and Ba, or one of Sr and a, M
2
is at least one metal selected from the group consisting of Mg and Zn, M
3
is at least one metal selected from the group consisting of Si and Ge, and a and b satisfy 0≦a≦0.5 and 0≦b≦0.5, respectively.
A still preferred one of fluorescent substances having the same crystal structure as diopside and comprising a compound of the above-noted general formula where m=n=1 has a composition in which M
1
is Ca and Sr, M
2
and M
3
are Mg and Si, respectively, and Ca is partially replaced with the activator Eu and which is represented by the general formula: Ca
1-c
Sr
c
Eu
d
MgSi
2
O
6
, wherein c and d satisfy 0<c≦0.1 and 0<d≦0.1, respectively.
Among fluorescent substances having the same crystal structure as akermanite, one comprising a compound of the above-noted general formula where m=2 and n=1 is preferable. A more preferable one as a fluorescent substance for vacuum ultraviolet radiation excited light-emitting devices has a composition in which M
1
is partially replaced with the activators Eu, or M
2
is partially replaced with the activators Mn, respectively, and which is represented by the general formula: (M
1
1-e
Eu
e
)
2
M
2
M
3
2
O
7
or M
1
2
(M
2
1-f
Mn
f
)M
3
2
O
7
, wherein M
1
is at l
Miyazaki Susumu
Ono Keiji
Sato Mineo
Takeda Takashi
Toda Kenji
Koslow C. Melissa
Sumitomo Chemical Company Limited
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