Rare-earth-doped oxysulfides for GaAs-pumped luminescent devices
- PDF / 480,355 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 19 Downloads / 201 Views
J - H E R E has b e e n much i n t e r e s t in p h o s p h o r s that e m i t v i s i b l e r a d i a t i o n when excited with i n f r a r e d light f r o m a s e m i c o n d u c t o r diode s o u r c e . 1 T h i s was s t i m u lated by the d e m o n s t r a t i o n 2 that y t t e r b i u m ions could be u s e d as an efficient s e n s i t i z e r , a b s o r b i n g r a d i a t i o n n e a r 9600A and t r a n s f e r r i n g it, by r a d i a t i o n l e s s c o u p l i n g , to v i s i b l e light e m i t t i n g a c t i v a t o r ions. The m o s t efficient h o s t s r e p o r t e d to date have a l l b e e n h a l i d e s : LaF3, s BaYFs, 4 YF3, s's and Y o x y c h l o r i d e s , s'7 In this p a p e r we r e p o r t a new c l a s s of p h o s p h o r h o s t s , the o x y s u l f i d e s of Y, La, and Gd: Y202S, La202S, and Gdg)2S. PREPARATION
OF
MATERIALS
That rare earth oxysulfides are an efficient family of phosphors is evident from the use of Y202S:Eu in color T V tubes. 8 Like Y202S:Eu, the oxysulfides studied here with ytterbium and either erbium or thulium activators, require careful control of synthesis conditions. One must avoid strongly reducing conditions, such as Hz or H2S atmospheres, probably because ytterbium and europium have stable divalent states. The synthesis used is the sulfur-carbonate flux method described by Royce, Smith, T h o m s e n and Yocom. 9 The Y203 used was of six 9's purity and the La2Os and GdzO3 were of five 9's purity, as was the YbzO3. The EreOs was of four 9's and the Tm203 was only three 9's. The compositions desired were prepared as mixed oxides by dissolving the required amount of each oxide in n i t r i c acid and then p r e c i p i t a t i n g the m i x e d o x a l a t e , which was d e c o m p o s e d to the oxide by f i r i n g in a i r at 750~ The oxides a r e t h o r o u g h l y mixed with NazCO~, S, and KzPO4 in the r a t i o of 5:2:2:1 by w e i g h t , r e s p e c t i v e l y ; P. N. YOCOM, J. P. WITTKE, and I. LADANY are Members of the Staff of RCA Laboratories, Princeton, N. J. This manuscript is based on a paper presented at the annual conference sponsored by the Electronic Materials Committee of the Institute of Metals Division of the MetallurgicalSociety of AIME and held August 30-September 2, 1970, in New York, City.
METALLURGICAL
TRANSACTIONS
and the m i x t u r e is f i r e d in a n A12Os c r u c i b l e with a tight fitting lid at l l 0 0 ~ for 1 hr in a i r . The flux to oxide r a t i o g i v e s only a s m a l l e x c e s s of flux for the y t t r i u m and l a r g e r e x c e s s e s for l a n t h a n u m and gadol i n i u m a s a c o n s e q u e n c e of the d i f f e r e n t a t o m i c w e i g h t s ; h o w e v e r u n l e s s the f i r i n g s a r e done u n d e r i n e r t a t m o s p h e r e this e x c e s s of flux is quite helpful to p r e v e n t oxidation. If a f t e r cooling the c h a r g e has a definite y e l low c o l o r , it can be s a f e l y a s s u m e d that no d e t r i m e n t a l oxidation has o c c u r r e d . The o
Data Loading...
