Interaction of triplet excitons with excited naphthalene and deuteronaphthalene molecules in benzophenone crystals
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OF
TRIPLET
EXCITONS
WITH
EXCITED
AND DEUTERONAPHTHALENE IN B E N Z O P H E N O N E
CRYSTALS UDC 535.343.2
A. S. G a e v s k i i , V. 1R. P r i i m a c h e k , a n d A. N. F a i d y s h
An i n c r e a s e in the intensity of the exciting light is shown to cause a significant d e c r e a s e in the quantum yield and r i s e t i m e of the sensitized p h o s p h o r e s c e n c e of impurity C10H8 and C10D8 in benzophenone c r y s t a l s . Nonlinear quenching of the impurity p h o s p h o r e s c e n c e occ u r s b e c a u s e one or two excitations a r e quenched in the interaction of triplet excitons with impurity molecules in the excited state in which they a r e left a f t e r the f i r s t exciton capture. E x p e r i m e n t s show the nature of the changes in the quantum yield and the r i s e t i m e of the i m p u r i t y p h o s p h o r e s c e n c e as the exciting-light intensity is varied f r o m 3.6 9 1012 to 6" 1016 p h o t o n s / c m 2. sec depends strongly on the impurity concentration, the c r y s t a l thickness, and the lifetime of the t r i p l e t state of the impurity molecules. The e x p e r i m e n t a l r e s u l t s a r e in good a g r e e m e n t with a proposed theory for the kinetics of the interaction of triplet excitons with impurity m o l e c u l e s in the ground and t r i p l e t states. 1. It has been shown [1-4] that the interaction of singlet [1, 2] and triplet [3, 4} excitons with excited m o l e c u l e s c a u s e s a significant d e c r e a s e in the quantum yields and r i s e t i m e s of impurity p h o s p h o r e s c e n c e when t h e r e is an i n c r e a s e in the intensity L of the exciting light. This quenching of impurity p h o s p h o r e s cence o c c u r s b e c a u s e one or two excitations a r e quenched in an interaction of excitons with i m p u r i t y m o l e cules in the excited state in which they a r e left a f t e r the f i r s t exciton capture 9 We r e p o r t h e r e a study of the quasinonlinear nature of naphthalene and deuteronaphthalene impurity p h o s p h o r e s c e n c e in benzophenone c r y s t a l s at 77~149 The high quantum yield of C10D8 (0.4-9.5) and the long lifetime of the triplet state (16 sec) p e r m i t o b s e r v a t i o n of a d e c r e a s e by a factor of hundreds in the quantum yield and p h o s p h o r e s c e n c e r i s e t i m e for an i n c r e a s e by a f a c t o r of thousands in the intensity of the exciting light. Purified benzophenone [5] is used in the study; in this m a t e r i a l the intensity of the p h o s p h o r e s cence of unknown i m p u r i t i e s (Z) does not exceed 10% of the intensity of the intrinsic p h o s p h o r e s c e n c e of the benzophenone c r y s t a l s . P h o s p h o r e s c e n c e of these c r y s t a l s is excited by DRSh-1000 lamp through a filter passing 365 am. An a b s o r b e r between the lamp and the s a m p l e p e r m i t s adjustment of the intensity of the light incident on the c r y s t a l . The p h o s p h o r e s c e n c e s p e c t r a a r e r e c o r d
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