Compositions – Inorganic luminescent compositions – Compositions containing halogen; e.g. – halides and oxyhalides
Patent
1985-01-22
1986-12-16
Straub, Gary P.
Compositions
Inorganic luminescent compositions
Compositions containing halogen; e.g., halides and oxyhalides
2523014F, C09K 1108
Patent
active
046295828
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a green-emitting phosphor.
BACKGROUND ART
As a means for simultaneously improving color rendering properties and light output, the three peak emission system is known which uses blue, green and red light-emitting phosphors having relatively narrow light-emission spectra and mixed in a predetermined ratio. In a flourescent lamp of this type which uses a mixture of three types of phosphors emitting light of significantly different colors, misregistration of colors is caused by the difference in decreases in light outputs of the respective phosphors after some operation time of the lamp. The misregistration degrades the product quality of the lamp.
With recent development in office equipment, the number of copying machines used is increasing. Especially, copying machines using fluorescent lamps as light sources are prevailing so much in view of energy conservation. In a copying machine of this type, a decrease in the light output after some ON time of the fluorescent lamp as the light source gives rise to a decrease in the copying speed. For this reason, the decrease in the light output over ON time counts more than the initial light output. However, the flourescent lamps as light sources which are used under high load experience more decreases in light output than the general fluorescent lamps.
An yttrium silicate phosphor {(Ye, Ce, Tb).sub.2 O.sub.3.SiO.sub.2 } activated by cerium and terbium emits green light and has high luminous efficacy, and is therefore used as a fluorescent lamp of the three peak emission type or a flourescent lamp as a copying machine light source. Although the yttrium silicate phosphor has high luminous efficacy, it goes through a relatively great decrease in the light output after some ON time.
The present invention has been made in consideration of this and has for its object to provide a novel green-emitting phosphor in which a decrease in light output during ON time is reduced to the minimum.
DISCLOSURE OF INVENTION
The present invention provides a green-emitting phosphor which is activated by cerium and terbium and which is represented by the general formula: O.sub.5.nSiO.sub.2 ytttrium, lanthanum, and gadolinium; A is at least one member selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs); and a>0, b>0, c>0, 0<a+b+3c<1, 1.times.10.sup.-5 .ltoreq.c.ltoreq.5.times.10.sup.-2, m>0, and n>0.
In the general formula (re.sub.1-a-b-3c Tb.sub.a Ce.sub.b A.sub.3c).sub.2 O.sub.3.mP.sub.2 O.sub.5.nSiO.sub.2, c represents the molar concentration of an alkaline metal defined by A. When the molar concentration c is below 1.times.10.sup.-5, effect of addition of the alkaline metal cannot be obtained. On the other hand, if the molar concentration c exceeds 5.times.10.sup.-2, the solid phase reaction of the alkaline metal is overly facilitated to make control of the solid reaction difficult.
BRIEF DESCRIPTION OF DRAWING
The accompanying FIGURE shows the spectrum of a phosphor according to an example of the present invention.
BEST MODE OF CARRYING OUT THE INVENTION
A fluorescent lamp of 38 W, i.e., FL-40. G/38 was manufactured using a phosphor of the present invention and following the conventional procedures. The obtained lamp was operated at a high load which was 30% higher than the rated load, and the decrease in the light output after 1,000 hour ON time was measured. As a result, the phosphor exhibited only 5 to 12% decrease in the light output while the conventional yttrium silicate phosphor activated by cerium and terbium represented by {(Y, Ce, Tb).sub.2 O.sub.3.SiO.sub.2)} exhibited 15% decrease. The phosphor of the present invention thus shows a considerable improvement in this respect. The light output of the phosphor of the present invention after 1,000 hour ON time is 107% at maximum when that of the conventional yttrium silicate phosphor activated with cerium and terbium was defined as 100%.
Since a phosphor of the present invention is a green-
REFERENCES:
patent: 3481884 (1969-12-01), Palilla et al.
patent: 4151443 (1979-04-01), Van den Boom et al.
patent: 4208611 (1980-06-01), Watanabe et al.
Asada Masao
Kimura Yoshio
Sugano Satoshi
Terashima Kenji
Straub Gary P.
Tokyo Shibaura Denki Kabushiki Kaisha
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