Red light emitting long afterglow photoluminescence phosphor...

Details Red light emitting long afterglow photoluminescence phosphor... Red light emitting long afterglow photoluminescence phosphor...

2001-02-20

2003-09-09

O'Shea, Sandra (Department: 2875)

Electric lamp and discharge devices

With luminescent solid or liquid material

With gaseous discharge medium

C313S483000, C313S485000, C252S30140S

Reexamination Certificate

active

06617781

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a red light emitting long afterglow photoluminescence phosphor which emits light being excited by visible rays and ultraviolet rays, and an afterglow lamp coated with this phosphor. More specifically, the present invention relates to the red light emitting long afterglow photoluminescence phosphor which is a rare earth oxysulfide phosphor activated by Europium and coactivated by a specified element, and an afterglow lamp coated with this phosphor.
TECHNICAL BACKGROUND
Phosphors, which are irradiated by the light from sunlight and from artificial lighting, and also phosphors, which exhibit afterglow for a relatively long time in dark places, are among phosphors, which are called light storing phosphors because this phenomenon can be repeated several times. Nowadays, with the ever-increasing complications of life, interest in disaster prevention has increased. Particularly the use of light storing phosphors afterglowing in dark places for disaster prevention has become progressively greater. Furthermore, the mixing of light storing phosphors into plastic allows the making of plates, sheets or the like, broadening their use in many fields.
The conventional substances used green light emitting ZnS: Cu phosphor as a light storing phosphor, but it did not provide sufficient performance. This is because this phosphor has the following intrinsic drawbacks. One is the phosphorescent luminance (luminance of the afterglow) which is not high enough to be found within several tens of hours. Another is the dark coloration of the surface due to the precipitation of colloidal metallic zinc on the surface of the crystal of the phosphor because of the decomposition due to the ultraviolet, the problem being a severe reduction or deterioration of the phosphorescent luminance. This deterioration accelerates particularly under the conditions of high temperature and humidity and usually, to ameliorate this drawback, a light proof treatment is applied on the surface of the ZnS:Cu phosphor, but the complete prevention still remains difficult. For this reason, the use of the ZnS:Cu phosphor has to be avoided in external places directly exposed to the sun's rays.
In this connection, a purplish-blue to green light emitting light storing phosphor in which the main crystals are comprised of a chemical compound represented by MAl
2
O
4
activated by divalent Europium in which M is comprised of at least one metallic element selected from the group consisting of Ca, Sr, Ba, has been disclosed in Japanese Non-examined Patent Publication No. 7-11250 issued in 1995. According to this publication, the phosphor is considered to have solved the intrinsic drawbacks of the here above-mentioned zinc sulfide phosphor. Furthermore, the main component of this phosphor has already been disclosed in U.S. Pat. No. 2,392,814, and in U.S. Pat. No. 3,294,699.
A blue-green light emitting long afterglow phosphor has been disclosed in the Japanese Non-examined Patent Publication No. 8-170076 issued in 1996 in which chemical compound is represented by MO.a(Al
l-b
B
b
)
2
O
3
:cR in which MO is at least one of divalent metallic oxides selected from the group consisting of MgO, CaO, SrO, and ZnO R is at least one of rare earth element selected from the group consisting of Pr, Nd, Dy, and Tm.
The long afterglow light storing phosphor of this type emitting purplish-blue to green light, have been much studied and are presently used, but among light storing phosphors emitting red light, are only known CaS:Eu, Tm which have short afterglow properties and a poor chemical stability. Where the phosphors are used such as decoration purpose, because a variety of tones of afterglow are necessary, the achievement of a chemically stable and long afterglow red light emitting long afterglow photo-luminescence phosphor has been needed. The hereabove long afterglow means the phosphorescence of photoluminescence with long afterglow time.
Furthermore, as phosphor excited by electron rays, a phosphor of rare earth oxysulfide exited by Europium has been developed and is used as the cathode ray tube being the cathode luminescence phosphor. But, because electron rays excite this phosphor, it has been rarely studied as photoluminescence phosphor excited by ultraviolet rays.
The inventors, by further improving this phosphor, have succeeded in developing a red light emitting long afterglow photoluminescence phosphor with fairly long afterglow properties. Therefore the first object of the present invention is to offer a red light emitting long afterglow photoluminescence phosphor excited by ultraviolet rays or the like, not by electron rays.
Incidentally, the purplish-blue to green light emitting light storing phosphors with long afterglow, have already been developed and are used for afterglow type lamps or the like, such as guide lamps.
Guide lamps are required to be installed at places where many people gather, such as theaters or hotels, by fire regulations in each city. In case of disasters such as an earthquake or a fire, or other accident, commercial power sources are shut down and it is assumed that backup power sources automatically switch on to turn such emergency guide lamps on for least 20 minutes. However, if the backup power sources were broken or their circuits were cut by the disaster, the guide lamps would turn off. In such cases, a complex underground street, a long tunnel, nighttime multistory buildings or the like would become very dangerous. Further, because the conventional guide lamps have a complicated structure, it takes much time and high cost to install them. Therefore, such guide lamps are rarely provided except in places where the laws require them.
Further, guide lamps are needed not only in emergency situations, and if most huge buildings, such as department stores, schools or factories, and regular buildings like stores and houses, are equipped with guide lamps with simple structures and lower costs, this would allow users to see their feet from the time when they turn off the switches on the lights of a room, corridor or staircase, until they reach the exit and, they would be more safe and comfortable.
In this connection, providing a light storing substance capable of absorbing and storing optical energy emitted from a light source on a supporting member, and as a shade positioned within where the light from the light source reaches, has been disclosed in Japanese Non-examined Patent Publication No.58-121088 issued Jul. 19, 1983. By using this light storing substance, backup power sources will not be required. However, the conventional light storing substances are disadvantageous in that they are chemically unstable and are apt to be deteriorated by ultra-violet rays, high temperatures, moisture or the like. Further, the afterglow of these light storing substances is dark and short. Furthermore, sufficient light cannot be obtained by coating a supporting member with a light storing substance.
The second object of the present invention is to offer a long afterglow lamp with a long afterglow without the emergency backup power sources.
DESCRIPTION OF THE INVENTION
In order to solve the above-mentioned problem, the present inventors eventually achieved the present invention, finding out that the problem can be solved by introducing a specific coactivator into the rare earth oxysulfide phosphor activated by Europium, as a result of research to improve long afterglow properties and phosphorescent luminance.
In sum, the red light emitting afterglow photoluminescence phosphor of the present invention comprises a rare earth oxysulfide phosphor which chemical formula includes following ranges:
Ln
2
O
2
S:Eu
x1
M
y
0.00001
≦x
≦0.5
0.00001
≦y
≦0.3
wherein Ln in the chemical formula is at least one member selected from the group consisting of Y, La, Gd and Lu; M is a coactivator which is at least one member selected from the group consisting of Nb, Ta and Ga.
 Ln
2
O
2
S:Eu
x
,Mg
y
,M′
z
0.00001
≦x
≦0.5
0.00001
≦y
≦0.3
0.00001
≦z
≦0.3
wherein Ln

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