UBC Theses and Dissertations

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UBC Theses and Dissertations

The fluorescent spectra of crystals of naphthalene and anthracene with added "impurities" of naphthacene… Lipsett, Frederick Roy 1951

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Iff/ R?. THE FLUORESCENT SPECTRA OF CRYSTALS OF NAPHTHALENE  AND ANTHRACENE WITH ADDED "IMPURITIES" OF NAPHTHACENE  AND1,2,5,6—PIB3NZANTHRACENE, UNDER X-RAY EXCITATION by FREDERICK ROY LIPSETT A THESIS SUBMITTED I N PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE I n t h e Oepartment o f PHYSICS We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e s t a n d a r d r e q u i r e d from c a n d i d a t e s f o r t h e degree o f MASTER OF APPLIES? SCIENCE Members o f t h e Department o f P h y s i c s THE UNIVERSITY OF BRITISH COLUMBIA Aug u s t , 1951 ABSTRACT When a c r y s t a l o f an t h r a c e n e w i t h a s m a l l added " i m p u r i t y " o f naphthacene i s e x c i t e d by X - r a d i a t i o n o r u l t r a -v i o l e t l i g h t t h e f l u o r e s c e n t spectrum i n c l u d e s o r c o n s i s t s almost t o t a l l y o f naphthacene bands. The energy absorbed by the a n t h r a c e n e i s s a i d t o have been t r a n s f e r r e d t o t h e naphthacene. The same r e s u l t i s o b t a i n e d w i t h c e r t a i n o t h e r " i m p u r i t i e s " and m a t r i x compounds. A l t h o u g h t h i s p r o c e s s had been known t o e x i s t f o r some time no d e t a i l e d q u a n t i t a t i v e e x p e r i m e n t s had been performed. The a u t h o r used an arrangement i n c l u d i n g a Beckman Model DU Qua r t z S p e c t r o p h o t o m e t e r used as a mono-chrometer and a 931-A p h o t o m u l t i p l i e r tube as a d e t e c t o r t o o b t a i n f l u o r e s c e n t s p e c t r a . T h i s arrangement combined v e r y g r e a t s e n s i t i v i t y w i t h g r e a t c o n v e n i e n c e o f o p e r a t i o n * The s p e c t r a o f c r y t a l s o f a n t h r a c e n e w i t h naphthacene, naphthalene w i t h naphthacene, and n a p h t h a l e n e w i t h 1,2 , 5 , 6 -d i b e n z a n t h r a c e n e were o b t a i n e d ; The maximum i n t e n s i t y o f -4 f l u o r e s c e n c e o f t h e i m p u r i t y bands o c c u r r e d a t 2 ,93 x 10 moles naphthacene p e r mole an t h r a c e n e i n t h e c r y s t a l s o f a n t h r a c e n e p l u s naphthacene: a t 3»38 x 10 moles naph-thacene p e r mole n a p h t h a l e n e i n the c r y s t a l s o f naphtha--4 l e n e p l u s naphthacene: and a t 1.01 x 10 moles 1,2 , 5 , 6 -d i b e n z a n t h r a c e n e p e r mole n a p h t h a l e n e i n t h e c r y s t a l s o f naphthalene p l u s 1 , 2 , 5 , 6 - d i b e n z a n t h r a c e n e . Tne f l u o r e s c e n t spectrum o f a c r y s t a l o f a n t h r a c e n e was o b t a i n e d u s i n g f i r s t X - r a y e x c i t a t i o n and t h e n u l t r a - v i o l e t e x c i t a t i o n . The two s o u r c e s o f e x c i t a t i o n gave r i s e t o d i f f e r e n t s p e c t r a . A t h e o r y o f t h e mechanism o f energy t r a n s f e r and a h y p o t h e t i c a l s e t o f energy l e v e l s f o r t h e c r y s t a l s w i t h added i m p u r i t i e s a re g i v e n . The method used t o grow some o f t h e c r y s t a l s used i n t h i s r e s e a r c h i s g i v e n i n an Appendix. ACKHOWLEDGBMENTS The a u t h o r w i s h e s t o make g r a t e f u l acknowledgement t o Dr. A. J . Dekker, under whose s u p e r v i s i o n t h e s e experiments were c a r r i e d o u t . The a u t h o r i s g r a t e f u l t o the N a t i o n a l R e s e a r c h C o u n c i l f o r a B u r s a r y and-a S t u d e n t s h i p , and t o t h e Defence R e s e a r c h Board f o r t h e purcha s e o f s u p p l i e s and equipment used i n t h e e x p e r i m e n t s . TABLE OF CONTENTS Page I . -INTRODUCTION 1 I I . EXPERIMENTAL ARRANGEMENT AND PROCEDURE . A. APPARATUS 3 B. PREPERATION OF CRYSTALS 9 I H . RESULTS, OBSERVATIONS, AND DISCUSSION A. RESULTS 1 1 B. OBSERVATIONS 21 C. DISCUSSION 24 I V . APPENDICES I . RESULTS OF OTHER AUTHORS AND RESULTS OF PRESENT EXPERIMENT JO I I . THE GROWTH OF SINGLE ORGANIC CRYSTALS 3 5 ILLUSTRATIONS ELATE PLATE PLATE PLATE PLATE PLATE PLATE PLATE Page I B l o c k Diagram o f A p p a r a t u s 4 I I C i r c u i t Diagram o f D. C. A m p l i f i e r 6 I I I Graph o f C o r r e c t i o n F a c t o r Ji/I v s . Wavelength 8 I V S p e c t r a o f C r y s t a l s o f Naphthelene w i t h Added 1 , 2 , 5 , 6 - d i b e n z a n t h r a c e n e 12 V S p e c t r a o f C r y s t a l s o f Naphthalene w i t h Added Naphthacene 13 VI S p e c t r a o f C r y s t a l s o f A n t h r a c e n e w i t h Added Naphthacene 14 V I I S p e c t r a o f an Anthr a c e n e C r y s t a l w i t h X - r a y E x c i t a t i o n and U l t r a - v i o l e t E x c i t a t i o n 15 V I I I Graph o f I n t e n s i t y o f 1 , 2 , 5 , 6 - d i b e n z a n t h r a c e n e Bands a t 44080 \A°"::and.-4250 A° v s . C o n c e n t r a t i o n i n C r y s t a l s o f Naphthalene w i t h Added 1 , 2 , 5 , 6 - d i b e n z a n t h r a c e n e 16 PLATE I X PLATE X PLATE X I Graph o f I n t e n s i t y o f 1 , 2 , 5 , 6 - d i b e n z a n t h r a c e n e Bands a t 4690 A° and 5040 A° v s . C o n c e n t r a t i o n i n C r y s t a l s o f Naphthalene w i t h Added 1 , 2 , 5 , 6 - d i b e n z a n t h r a c e n e 17 Graph o f I n t e n s i t y o f Naphthacene Bands a t 4965 A° and 5285 A° v s . C o n c e n t r a t i o n i n C r y s t a l s o f Naphthalene w i t h Added Naphthacene 18 Graph o f I n t e n s i t y o f Naphthacene Band a t 568O A° v s . C o n c e n t r a t i o n i n C r y s t a l s o f Naphthalene w i t h Added Naphthacene 19 PLATE X I I Graph o f I n t e n s i t y o f Naphthacene Bands a t 5520 A° and 5735 A° v s . C o n c e n t r a t i o n i n C r y s t a l s o f Ant h r a c e n e w i t h Added Naphthacene 20 PLATE X I I I H y p o t h e t i c a l Set o f Energy L e v e l s PLATE X I V C o n t a i n e r s f o r t h e Growth o f C r y s t a l s PLATE XV Arrangement o f Furnace f o r the Growth o f C r y s t a l s PLATE XVI Graph o f Thermocouple Temperatures i n Furnace v s . H e a t e r v o l t a g e 28 37 39 40 I . INTRODUCTION 1 2 G-anguley and Bowen found t h a t when a s m a l l q u a n t i t y o f naphthacene (about one p a r t i n 10^) i s added t o a n t h r a c e n e t h e f l u o r e s c e n c e o f t h e an t h r a c e n e i s s u p p r e s s e d and naphthacene f l u o r e s c e n e c e o f h i g h e f f i c i e n c y a p p e a r s . As t h e c o n c e n t r a t i o n o f naphthacene i s i n c r e a s e d t h e i n t e n s i t y o f t h e naphthacene f l u o r e s c e n c e i n c r e a s e s and t h a t o f t h e a n t h r a c e n e d e c r e a s e s . F i n a l l y a t a c o n c e n t r a t i o n -4 o f 2.93 x 10 moles naphthacene p e r mole a n t h r a c e n e t h e naphthacene f l u o r e s c e n c e i s more t h a n one hundred t i m e s as i n t e n s e as t h e a n t h r a c e n e f l u o r e s c e n c e . The same p r o c e s s t a k e s p l a c e when s m a l l amounts o f naphthacene a r e added t o n a p h t h a l e n e , o r when a n t h r a c e n e i s added t o n a p h t h a l e n e , and so on. I n t h e s e p a r t i c u l a r c a ses t h e p r o c e s s t a k e s p l a c e o n l y i n s o l i d s o l u t i o n s , n o t i n l i q u i d s o l u t i o n s o r i n g e l a t i n s o l u t i o n s . A n e c e s s a r y c o n d i t i o n f o r i t s p r e s e n c e i s t h a t t h e f l u o r e s c e n c e o f t h e i m p u r i t y m o l e c u l e s t a k e p l a c e a t e q u a l o r l o n g e r w avelengths t h a n t h e f l u o r e s c e n c e o f t h e m a t r i x compound. I t does not o c c u r by r e a b s o r b t i o n o f t h e m a t r i x f l u o r e s c e n c e by t h e i m p u r i t y m o l e c u l e s , f o r su c h a p r o c e s s would n ot e x p l a i n t h e h i g h e f f i c i e n c y o f 2 f l u o r e s c e n c e found e x p e r i m e n t a l l y . Hence t h e e x c i t a t i o n energy absorbed by t h e m a t r i x i s s a i d t o have been t r a n s f e r r e d t o t h e i m p u r i t y m o l e c u l e s . A s i m i l a r p r o c e s s t a k e s p l a c e when c e r t a i n 2 l i q u i d s o l u t i o n s a r e e x c i t e d by u l t r a - v i o l e t l i g h t o r 4 gamma-rays . F o r example, when a s o l u t i o n o f about 5 gms, per l i t e r o f t e r p h e n y l i n x y l e n e i s bombarded by gamma-rays, f l u o r e s c e n t l i g h t c h a r a c t e r i s t i c o f t e r p h e n y l appears w h i c h i s o f t h e o r d e r o f one hundred t i m e s as i n t e n s e as would be e x p e c t e d i f t h e amount o f t e r p h e n y l i n s o l u t i o n were bombarded i n t h e s o l i d s t a t e . The energy absorbed by t h e s o l v e n t i s s a i d t o have been t r a n s f e r r e d t o t h e s o l u t e . I t w i l l be seen from t h e f o r e g o i n g t h a t t h e p r o c e s s o f t h e t r a n s f e r o f energy i n c e r t a i n s o l i d and l i q u i d s o l u t i o n s i s a common o c c u r r e n c e . Hence i t i s s u p r i s i n g t h a t p r a c t i c a l l y no q u a n t i t a t i v e i n v e s t i g a t i o n s o f t h i s phenomenon, a t l e a s t i n t h e s o l i d casies, have been c a r r i e d o u t . Such s t u d i e s a r e o b v i o u s l y needed i f a c o r r e c t e x p l a n a t i o n o f t h e t r a n s f e r p r o c e s s i s t o be made. The r e a s o n f o r t h i s l a c k o f r e s e a r c h has been the l a c k o f adequate a p p a r a t u s . The change i n t h e r e l a t i v e i n t e n s i t i e s o f the m a t r i x and i m p u r i t y f l u o r e s c e n c e i s enormous, and cannot be s t u d i e d a d e q u a t e l y by means o f p h o t o g r a p h i c p l a t e s , and t h e p h o t o c e l l s used i n c o m b i n a t i o n w i t h f i l t e r s by some a u t h o r s a r e not adequate f o r s t u d y i n g t h e band s t r u c t u r e o f t h e f l u o r e s c e n c e . The i n t r o d u c t i o n o f t h e new p h o t o m u l t i p l i e r 5 t u b e s ^ has o b v i a t e d t h e p r e v i o u s d i f f i c u l t i e s . When used as d e t e c t o r s i n a monochrometer t h e s e tubes a r e e x t r e m e l y s e n s i t i v e t o a wide range o f i n t e n s i t i e s , and w i t h s u i t a b l e c a l i b r a t i o n t h e y a r e w e l l adapted t o g i v e a l l t h e i n f o r m a t i o n n e c e s s a r y q u a n t i t a t i v e s t u d i e s o f t h e s p e c t r a i n v o l v e d i n t h e t r a n s f e r p r o c e s s . I I . EXPERIMENTAL ARRANGEMENT AND PROCEDURE A» APPARATUS A b l o c k d i a g r a m o f t h e a p p a r a t u s i s g i v e n i n P l a t e I . The c r y s t a l under e x a m i n a t i o n was i r r a d i a t e d w i t h X - r a y s o f 6j> KVP and 15 mA f r o m a P r o f e x r a y p o r t a b l e X - r a y u n i t , i n o r d e r t o produce f l u o r e s c e n t l i g h t . The l i g h t from the c r y s t a l was passed i n t o t he e n t r a n c e s l i t o f a Beckman Model DU Quartz S p e c t r o p h o t o m e t e r , w h i c h was used as a monochrometer. F l u o r e s c e n t lighvb o f a p a r t i c u l a r w a v e l e n g t h was passed f r o m t h e e x i t s l i t o f t h e s p e c t r o p h o t o m e t e r on t o t h e photocathode o f a s e l e c t e d 931-A p h o t o m u l t i p l i e r t u b e . The tube was housed i n a l i g h t - t i g h t b r a s s box w h i c h was screwed d i r e c t l y on t o t h e s p e c t r o p h o t o m e t e r i n p l a c e o f t h e p h o t o c e l l s o r d i n a r i l y used w i t h t h i s i n s t r u m e n t . The o u t p u t o f t h e p h o t o m u l t i p l i e r tube was a m p l i f i e d by a D.C. a m p l i f i e r w i t h t h r e e o v e r l a p p i n g ranges o f s e n s i t i v i t y , and t h e o u t p u t f r o m the a m p l i f i e r was r e a d on a microammeter. The r e a d i n g o f the microammeter, when c o r r e c t e d , gave t h e i n t e n s i t y o f t h e f l u o r e s c e n t l i g h t o f t h e c r y s t a l a t t h e wa v e l e n g t h passed by t h e s p e c t r o p h o t o m e t e r . T h i s arrangement was f i r s t used by B u r d e t t and Jo n e s ^ , a l t h o u g h t h e s e a u t h o r s employed t h e p h o t o c e l l s s u p p l i e d w i t h t h e s p e c t r o p h o t o m e t e r . These were s u f f i c i e n t l y s e n s i t i v e f o r t h e s p e c t r a t h e a u t h o r s were s t u d y i n g , a l t h o u g h t h e y p l a n n e d the s u b s t i t u t i o n BECKMAN MODEL DU QUARTZ SPECTROPHOTOMETER CRYSTAL X-RAY TUBE HEAD HIGH VOLTAGE NEGATIVE D.C. REGULATED SUPPLY D.C. AMPLIFIER MICROAMMETER SELECTED 931-A PHOTOMULTIPLIER TUBE LIGHT-TIGHT BRASS BOX P l a t e I . B l o c k d i a g r a m o f a p p a r a t u s . o f a p h o t o m u l t i p l i e r tube f o r f e e b l e r s p e c t r a . The arrangement has many advantages o v e r t h e c o n v e n t i o n a l use o f a s p e c t r o g r a p h and a mi c r o p h o t o m e t e r . The s e n s i t i v i t y o f t h e p h o t o m u l t i p l i e r tube i s much g r e a t e r t h a n t h a t o f a p h o t o g r a p h i c p l a t e , and t h e range o f i n t e n s i t i e s i t w i l l c o v e r i s much l a r g e r . F o r example, t h e spectrum o f a c r y s t a l o f n a p h t h a l e n e w i t h added 1,2,5,6-dibenzanthracene was o b t a i n e d c o m p l e t e l y i n about two hours w i t h t h e p r e s e n t a p p a r a t u s , w h i l e a n i n e - h o u r i exposure o f a s e n s i t i v e p h o t o g r a p h i c p l a t e i n a q u a r t z s p e c t r o g r a p h s u f f i c e d o n l y t o show t h e n a p h t h a l e n e band i n t h i s c r y s t a l . I n t e n s i t i e s a r e r e a d d i r e c t l y , i n s t e a d o f r e q u i r i n g the use o f a mi c r o p h o t o m e t e r , and t h e h a n d l i n g and d e v e l o p i n g o f p l a t e s i s o m i t t e d . P r a c t i c a l l y a l l : t h e components o f t h e arrangement a r e s t a n d a r d p i e c e s o f equipment s u c h as may be found i n any w e l l equipped l a b o r a t o r y . The o n l y components c o n s t r u c t e d by t h e a u t h o r were t h e l i g h t - t i g h t box h o u s i n g t h e p h o t o m u l t i p l i e r , t u b e and t h e D.C. a m p l i f i e r . A c i r c u i t d i a g r a m o f t h e a m p l i f i e r , i s g i v e n i n P l a t e I I . The r e g u l a t e d h i g h v o l t a g e r D.C. power s u p p l y , used f o r s u p p l y i n g v o l t a g e s t o t h e dynodes o f t h e p h o t o m u l t i p l i e r tube was b u i l t i n t h e Department o f P h y s i c s . A l t h o u g h t h e method used t o o b t a i n t h e f l u o r e s c e n t s p e c t r a i s s u p e r i o r t o c o n v e n t i o n a l methods, t h e p r e s e n t arrangement does n ot f u l l y e x p l o i t a l l t h e p o s s i b i l i t i e s o f t h e method. X - r a y s o f much h i g h e r i n t e n s i t y c o u l d be 6 J 7 G T 6 J 7 G T OLOW 10 Microammeter 0-150,* A 1000 >>— 1 750 1500 =190 Volts oINPUT Coarse 8 fine zero adjustment tor microammeter Selector switch for sensitivity range P l a t e I I . C i r c u i t d i a g r a m o f D. C. a m p l i f i e r . IS, ON 7 used t o produce f l u o r e s c e n t l i g h t o f c o r r e s p o n d i n g l y h i g h e r i n t e n s i t y , and t h e f l u o r e s c e n t l i g h t c o u l d be c o l l e c t e d more e f f i c i e n t l y f r o m p o l i s h e d s i n g l e c r y s t a l s w i t h a r e f l e c t o r and c o l l e c t i n g l e n s . A monochrometer w i t h a more c o n v e n i e n t m e c h a n i c a l arrangement c o u l d be c o n s t r u c t e d , w i t h h i g h e r r e s o l v i n g power i f d e s i r e d . The l i g h t p a s s i n g from t h e e x i t s l i t o f t h e monochrometer c o u l d be f o c u s s e d on t h e e n t i r e p hotocathode o f t h e p h o t o m u l t i p l i e r by a s u i t a b l e l e n s . F i n a l l y , t h e f l u o r e s c e n t l i g h t f r o m t h e c r y s t a l c o u l d be "chopped": t h i s would a l l o w t h e s u b s t i t u t i o n o f an A.C. a m p l i f i e r f o r t h e p r e s e n t D.C. a m p l i f i e r , w i t h the advantages o f h i g h e r g a i n and g r e a t e r s t a b i l i t y . The d i s p e r s i o n o f t h e s p e c t r o p h o t o m e t e r changes w i t h the w a v e l e n g t h o f l i g h t p a s s e d , and t h e s e n s i t i v i t y ^ o f the p h o t o m u l t i p l i e r changes w i t h t h e w a v e l e n g t h o f t h e l i g h t f a l l i n g on the p h o t o c a t h o d e . Hence a t each w a v e l e n g t h a t w h i c h a r e a d i n g i s t a k e n i t i s n e c e s s a r y t o a p p l y a c o r r e c t i o n i n o r d e r t o compensate f o r t h e s e changes. T h i s c o r r e c t i o n was o b t a i n e d as f o l l o w s . L i g h t f r o m a c l e a r t u n g s t e n lamp was passed t h r o u g h t h e s p e c t r o p h o t o m e t e r , and r e a d i n g s were t a k e n o f t h e i n t e n s i t y o f t h e l i g h t a t i n t e r v a l s o f 100 A° o v e r t h e w a v e l e n g t h range 3000 - 6000 A ° . The lamp, when o p e r a t e d a t i t s r a t e d v o l t a g e , was assumed t o be a b l a c k body w i t h a t e m p e r a t u r e o f 2850 °E. The i n t e n s i t y o f r a d i a t i o n o f a b l a c k body o f t h i s t e m p e r a t u r e J , was c a l c u l a t e d a t each w a v e l e n g t h a t .which a r e a d i n g 7 was t a k e n w i t h t h e a i d o f t a b l e s g i v e n by JahrCke and Emde . WAVELENGTH IN A P l a t e I I I . C o r r e c t i o n f a c t o r , J"/I, f o r d i s p e r s i o n o f s p e c t r o p h o t o m e t e r and s p e c t r a l c h a r a c t e r i s t i c s o f p h o t o m u l t i p l i e r t u b e . The i n t e n s i t y J was t h e n d i v i d e d by t h e microammeter r e a d i n g I a t each w a v e l e n g t h , and the r e s u l t i n g c o r r e c t i o n f a c t o r J / I was p l o t t e d on a graph, as shown i n P l a t e I I I . When the spectrum o f a c r y s t a l was, t o be o b t a i n e d , the c u r r e n t r e a d f r o m t h e microammeter was m u l t i p l i e d a t each w a v e l e n g t h by the a p p r o p r i a t e v a l u e o f J/l r e a d f r o m t h e graph. B. PREPERATION OF CRYSTALS I n s t u d i e s o f t h e t r a n s f e r o f energy i t i s e s s e n t i a l t o use o n l y m a t e r i a l s o f t h e h i g h e s t p u r i t y . The a u t h o r was f o r t u n a t e l y a b l e t o o b t a i n m a t e r i a l s f o r t h e p r e s e n t e x p e r i m e n t s c o m m e r c i a l l y . The s o u r c e s o f s u p p l y were as f o l l o w s : N a p h t h a l e n e : s u b l i m e d i n a i r from s t o c k s u p p l i e d by t h e Eastman Kodak Co., R o c h e s t e r , N. Y., A n t h r a c e n e : " S c i n t i l l a t i o n Grade" s u p p l i e d by the R e i l l y Tar and Ch e m i c a l C o r p o r a t i o n , New Y o r k , N. Y., Naphthacene: s u p p l i e d by t h e Eastman Kodak Co., 1 , 2 , 5 , 6 - d i b e n z a n t h r a c e n e : s u p p l i e d by t h e Eastman Kodak Co. A sample o f the ant h r a c e n e used was s u b j e c t e d t o f u r t h e r p u r i f i c a t i o n i n a ch r o m a t o g r a p h i c column by Dr. C. R e i d , o f the.Department o f C h e m i s t r y , U n i v e r s i t y o f B r i t i s h Columbia, and showed no e v i d e n c e o f change. Some n a p h t h a l e n e o b t a i n e d f r o m a w e l l known company showed v i s i b l e f l u o r e s c e n c e bands a t t r i b u t a b l e t o i m p u r i t i e s o f naphthacene, 10 1,2,5»6-dibenzanthracene, and a t h i r d u n i d e n t i f i a b l e ~ i m p u r i t y . I t was d i s c a r d e d i n f a v o u r o f n a p h t h a l e n e s u p p l i e d by t h e Eastman Kodak Co. Some an t h r a c e n e p u r c h a s e d f r o m t h e R e i l l y Tar and C h e m i c a l C o r p o r a t i o n subsequent t o t h e e x c e c u t i o n o f the ex p e r i m e n t s was o f much l o w e r p u r i t y t h a n t h a t o r i g i n a l l y p u r c h a s e d . The p r o c e d u r e adopted f o r p r e p a r i n g c r y s t a l s was as f o l l o w s . About 0.0200 gms. o f i m p u r i t y and 20.00 gms. o f m a t r i x compound were c a r e f u l l y weighed on an a c c u r a t e b a l a n c e . These compounds were t h e n p l a c e d c o n s e c u t i v e l y i n a t e s t - t u b e o r s p e c i a l c o n t a i n e r and rew e i g h e d . The m i x t u r e was then- h e a t e d s u f f i c i e n t l y t o m e l t t h e compounds . and t o a l l o w t h e i m p u r i t y t o d i s s o l v e * The i m p u r i t i e s go i n t o s o l u t i o n v e r y q u i c k l y . The m i x t u r e was t h e n a l l o w e d t o c o o l t o f o r m a s t a n d a r d p o l y c r y s t a l l i n e s o l i d s o l u t i o n , o f a c c u r a t e l y known c o n c e n t r a t i o n . M i x t u r e s o f n a p h t h a l e n e p l u s an i m p u r i t y were h e a t e d i n a i r by means o f a bunsen b u r n e r , w h i l e t h e s t a n d a r d m i x t u r e o f a n t h r a c e n e p l u s naphthacene was placed- i n a c o n t a i n e r w h i c h was eva c u a t e d w i t h a fore-pump, .sealed o f f , and h e a t e d i n a f u r n a c e . The m i x t u r e s were removed f r o m t h e c o n t a i n e r s by sawing t h e g l a s s f rom around them w i t h a diamond saw. I n d i v i d u a l c r y s t a l s f o r ex p e r i m e n t s were made by co m b i n i n g a s m a l l amount o f t h e s t a n d a r d m i x t u r e w i t h s u f f i c i e n t o f the m a t r i x compound t o g i v e a c r y s t a l o f t h e r e q u i r e d c o n c e n t r a t i o n . Some o f t h e s e mixes were t h e n t r e a t e d i n t h e same manner as t h e s t a n d a r d m i x t u r e s , 11 w h i l e o t h e r s were grown i n t o s i n g l e c r y s t a l s by a method d e s c r i b e d i n A p p e n d i x I I . There was no n o t i c e a b l e d i f f e r e n c e between t h e s p e c t r a produced by t h e p o l y c r y s t a l l i n e samples and t h e s i n g l e c r y s t a l samples. I I I . RESULTS. OBSERVATIONS. AND DISCUSSION  A. RESULTS The spectrum o f a s i n g l e c r y s t a l o f na p h t h a l e n e and t h e s p e c t r a o f a s e l e c t i o n o f c r y s t a l s o f n a p h t h a l e n e w i t h added 1 , 2,5,6-dibenzanthracene a r e g i v e n i n P l a t e I V . S i m i l a r s p e c t r a f o r n a p h t h a l e n e w i t h added naphthacene a r e g i v e n i n P l a t e V, and f o r a n t h r a c e n e w i t h added naphthacene i n P l a t e V I . The s p e c t r a o f a c r y s t a l o f an t h r a c e n e under e x c i t a t i o n f r om X-rays and fr o m u l t r a - v i o l e t l i g h t ©'f 3650 A° a r e shown i n P l a t e V I I . A graph showing t h e v a r i a t i o n w i t h c o n c e n t r a t i o n o f t h e i n t e n s i t y o f t h e 1 , 2,5>6-dibenzanthracene bands a t 4080 A° and 4250 A° r e l a t i v e t o t h e nap h t h a l e n e band a t 3410 A° i s g i v e n i n P l a t e V I I I , w h i l e a gra p h f o r t h e 1 , 2,5,6-dibenzanthracene bands a t 4690 A° and 5040 A° i s g i v e n i n P l a t e I X . S i m i l a r graphs f o r t h e naphthacene bands a t 4965 A 0 and 5285 A° r e l a t i v e t o the n a p h t h a l e n e band a t 3415 A° a r e g i v e n i n P l a t e X, and f o r t h e naphthacene band a t 568O A° i n P l a t e X I . A gra p h showing t h e v a r i a t i o n w i t h c o n c e n t r a t i o n o f t h e naphthacene bands a t 5320 A° and 5735 A? r e l a t i v e t o the anthracene band a t 4445 A° i s g i v e n i n P l a t e X I I . WAVELENGTH IN I P l a t e I V . S p e c t r a o f c r y s t a l s o f naphthalene w i t h added 1,2,5,6-dibenzanthracene, w i t h t h e f o l l o w i n g c o n c e n t r a t i o n s i n moles 1,2,5,6-dibenzanthracene p e r mole n a p h t h a l e n e : A. 0 Bi 4.14 x 1 0 ~ 6 C. 1.01 x 10"-5 D. 7.42 x 10"-5 E. 1.01 x 1 0 ~ 4 E. 1 .39 x 1 0 ~ 4 H WAVELENGTH IN % P l a t e V. S p e c t r a o f c r y s t a l s o f naphthalene w i t h added naphthacene, w i t h t h e f o l l o w i n g c o n c e n t r a t i o n s i n moles naphthacene-per mole n a p h t h a l e n e : A. 0 c B.. 5.62 x 10-7 c. 5.67 x 10-6 D. 3.38 x 1 0 " 5 E„ 8.43 x 10"> F. 1.70 x 10 H 4 * WAVELENGTH IN A P l a t e V I . Spectra of c r y s t a l s of anthracene w i t h added naphthacene, w i t h the f o l l o w i n g concentrations i n moles naphthacene per mole anthracene: A. 0 B. 8.68 x 10~ 7 C. 2.24 x 10"-5 D. 1.04 x 1 0 " 4 E. 2.93 x 10" 4 F.. 9.54 x 10~ 4 1 5 WAVELENGTH IN A P l a t e V I I . Spectra of an anthracene c r y s t a l : A. under X-ray e x c i t a t i o n B. under e x c i t a t i o n from u l t r a - v i o l e t l i g h t of 3 6 5 0 A° -5 -4-4 5 6 7 8 10 2 3 4 5 6 78 10 2 CONCENTRATION - MOLES 1,2,5.6-DIBENZANTHRACENE PER MOLE N A P H T H A L E N E P l a t e V I I I . I n t e n s i t i e s o f 1,2,j?>6-dibenzanthracene bands a t 4080 A° and 42j?0 A ° , r e l a t i v e t o na p h t h a l e n e band a t 3410 A°. 3 -17 I I 1 1 M l 1 I 1 1 1 M i l 1 - 1 4 5 6 7 8 I 0 5 2 3 4 5 6 7 8 I 0 " 4 2 3 CONCENTRATION - MOLES 1 ,2 ,5 ,6-DIBENZANTHRACENE PER MOLE NAPHTHALENE P l a t e I X . I n t e n s i t i e s o f 1,2,5,6-dibenzanthracene bands a t 4690 A° and 5040 A ° , r e l a t i v e t o n a p h t h a l e n e band a t 5410 A°. 18 7 r— 6 — O in2' M i l l I I I I I M i l 1 1 1 1 1 1 1 1 1 I 5 6 8 id" 6 2 3 4 5 6 8 I0~S 2 3 4 5 6 8 i d " 4 2 CONCENTRATION-MOLES NAPHTHACENE/MOLE NAPHTHALENE P l a t e X. I n t e n s i t i e s of naphthacene bands at 4965 A° and 5285 A 0, r e l a t i v e to naphthalene band at J415 A 0. 19 5 6 8 I0"6 2 3 4 5 6 8 10*5 2 3 4 5 6 8 lO*4" 2 CONCENTRATION-MOLES N A P H T H A C E N E / M O L E NAPHTHALENE P l a t e X I . I n t e n s i t y o f naphthacene band a t 5680 A°, r e l a t i v e t o naphthalene band a t 3415 A ° . 2 20 LLI i MI m u i i i 11 m i i i 11 i i i i i -6 -5 - 4 -3 10 2 3 4 5 7 10 2 3 4 5 7 10 2 3 4 5 7 10 CONCENTRATION-MOLES NAPHTHACENE / MOLE ANTRRACENE P l a t e X I I . I n t e n s i t i e s o f naphthacene bands a t 5320 A° and 5735 A°, r e l a t i v e t o anthracene band at 4445 A ° . 21 The p r i n c i p l e r e s u l t s o f t h e experiment a r e summarised i n Table I . The d e t a i l e d r e s u l t s f o r a l l s p e c t r a o b t a i n e d a r e t a b u l a t e d i n Appendix 1, t o g e t h e r w i t h some r e s u l t s o b t a i n e d by o t h e r a u t h o r s . B. OBSERVATIONS The s p e c t r a o f t h e c r y s t a l s o f n a p h t h a l e n e w i t h added naphthacene and o f anthracene w i t h added naphthacene ( P l a t e s V, V I , and T a b l e I ) show t h a t t h e w a v e l e n g t h s o f t h e naphthacene i m p u r i t y bands are s h o r t e r when th e naphthacene i s i n s o l i d s o l u t i o n i n n a p h t h a l e n e t h a n when i t i s i n s o l i d s o l u t i o n i n a n t h r a c e n e . Thus i t may be c o n c l u d e d t h a t t h e wavelengths e x h i b i t e d by t h e naphthacene depend upon the m a t r i x i n w h i c h t h e naphthacene i s d i s s o l v e d . That t h e naphthacene and 1 , 2 , 5 , 6 - d i b e n z a n t h r a c e n e bands appear a t s t i l l d i f f e r e n t w a velengths i n l i q u i d s o l u t i o n s i s shown f r o m t h e r e s u l t s o f o t h e r a u t h o r s i n T a b l e I I , A ppendix I . These r e s u l t s i n d i c a t e t h e p o s s i b i l i t y t h a t i n g e n e r a l f o r s u c c e s s i v e l y s h o r t e r w a v e l e n g t h s o f m a t r i x f l u o r e s c e n c e , t h e f l u o r e s c e n c e o f t h e i m p u r i t y moves t o s h o r t e r w a v e l e n g t h s . The s p e c t r a o f t h e c r y s t a l s w i t h added i m p u r i t i e s ( P l a t e s I V , V, and V I ) show t h a t t h e p r o p o r t i o n o f energy t r a n s f e r r e d t o t h e v a r i o u s i m p u r i t y bands i s not e q u a l a t a l l c o n c e n t r a t i o n s . F o r example, i n the s p e c t r a o f t h e c r y s t a l s o f a n t h r a c e n e w i t h added naphthacene ( P l a t e V I ) the naphthacene band a t 5035 A° becomes almost c o m p l e t e l y o b s c u r e d by t h e l o n g e r w a v e l e n g t h bands as t h e c o n c e n t r a t i o n T a b l e I . P r i n c i p l e R e s u l t s M a t r i x I m p u r i t y M a t r i x bands A° I m p u r i t y bands A : 0 C o n c e n t r a t i o n f o r maximum t r a n s f e r , moles i m p u r i t y p e r mole m a t r i x Naphthalene 3430 Naphthalene 1 , 2 , 5 , 6 - d i b e n z -anthrac ene 3410 3 5 2 0 , 3 7 2 0 , 4080 4 2 5 0 , 4690, 5040 1 . 0 1 x 1 0 ~4 Naphthalene Naphthac ene 3415 4 9 6 5 , 5 2 8 5 , 5680 3 . 3 8 x l O " 5 Anthracene (36^0 A° e x c i t a t i o n ) 4040, 4220, 4460, 4690 A n t h r a c ene (X - r a y e x c i t a t i o n ) 4 4 7 5 , 4 7 1 0 , 5040 Anthracene Naphthacene 4 4 4 5 , 4710 5 0 3 5 , 5 3 2 0 , 5735 2.93 x 1 0 " 4 25 o f naphthacene i n c r e a s e s . I n t h e c r y s t a l s o f n a p h t h a l e n e p l u s naphthacene ( P l a t e V) the s h o r t w a v e l e n g t h hand a t 4965 A° i s more i n t e n s e t h a n t h e hand a t 5285 A° a t a -7 c o n c e n t r a t i o n o f ^ x 10 moles naphthacene p e r mole n a p h t h a l e n e , w h i l e a t l a r g e r c o n c e n t r a t i o n s t h e hand a t 5285 A° i s more i n t e n s e . The same change i n r e l a t i v e i n t e n s i t i e s o c c u r s between the bands a t 4080 A° and 4250 A° i n t h e c r y s t a l s o f n a p h t h a l e n e p l u s 1 , 2 , 5 , 6 - d i b e n z a n t h r a c e n e ( P l a t e I T ) . The c o n c e n t r a t i o n s f o r maximum t r a n s f e r o f energy ( T a b l e I ) show no o b v i o u s r e l a t i o n s h i p t o one a n o t h e r , a p a r t f r o m the f a c t t h a t a l l t h e s e c o n c e n t r a t i o n s a r e v e r y s m a l l . The t r a n s f e r i s most e f f i c i e n t i n t h e c r y s t a l s o f anthracene p l u s naphthacene ( P l a t e X I I ) . The wave l e n g t h r e g i o n between t h e i m p u r i t y f l u o r e s c e n t bands and t h e m a t r i x f l u o r e s c e n t bands i s i n t h i s case t h e s h o r t e s t o f any o f the t h r e e c o m b i n a t i o n s i n v e s t i g a t e d . The graphs showing t h e i n t e n s i t i e s o f t h e i m p u r i t y bands r e l a t i v e t o t h e m a t r i x band ( P l a t e s V I I I t o X I I ) a r e s i m i l a r t o one a n o t h e r i n t h e i r g e n e r a l appearance, but the s l o p e s o f t h e c u r v e s on e i t h e r s i d e o f the maxima a r e v e r y l a r g e f o r the c r y s t a l s o f n a p h t h a l e n e p l u s 1 , 2 , 5 , 6 - d i b e n z a n t h r a c e n e ( P l a t e s V I I I and I X ) , s m a l l e r f o r the c r y s t a l s o f a n t h r a c e n e p l u s naphthacene ( P l a t e t . x i l ) , and, c o m p a r i t i v e l y , v e r y s m a l l f o r t h e c r y s t a l s o f n a p h t h a l e n e p l u s naphthacene ( P l a t e s X and X I ) . F o r each o f the c o m b i n a t i o n s o f m a t r i x p l u s i m p u r i t y s t u d i e d t h e two 24 i m p u r i t y bands o f l o n g e s t w a v e l e n g t h form a d o u b l e t , t h e components o f w h i c h ( e x c e p t i n the case o f c r y s t a l s o f n a p h t h a l e n e p l u s naphthacene a t v e r y low c o n c e n t r a t i o n s ) m a i n t a i n v e r y n e a r l y t h e same r e l a t i v e i n t e n s i t i e s t o one a n o t h e r over t h e c o n c e n t r a t i o n ranges i n v e s t i g a t e d . 0. DISCUSSION I n o r d e r t o be complete any t h e o r y o f the t r a n s f e r o f energy must e x p l a i n why t h e r e s h o u l d be any t r a n s f e r , o f energy a t a l l , and why t h e p r o c e s s s h o u l d be so e f f i c i e n t . I t must e x p l a i n why t h e wavelengths o f t h e i m p u r i t y f l u o r e s c e n c e bands s h o u l d depend upon t h e m a t r i x i n w h i c h the i m p u r i t y i s d i s s o l v e d , and why the i n t e n s i t i e s o f t h e i m p u r i t y f l u o r e s c e n c e bands depend upon the c o n c e n t r a t i o n t h e way t h e y do. There a r e t h r e e p o s s i b l e ways i n w h i c h t h e t r a n s f e r o f energy might t a k e p l a c e . 1. E x c i t a t i o n energy absorbed by t h e m a t r i x might be r e e m i t t e d as f l u o r e s c e n t l i g h t by t h e m a t r i x , and . t h i s f l u o r e s c e n t l i g h t might be r e a b s o r b e d by the i m p u r i t y m o l e c u l e s and s u b s e q u e n t l y r e e m i t t e d by t h e i m p u r i t y m o l e c u l e s . Such a p r o c e s s , however, would not account f o r t h e h i g h e f f i c i e n c y o f t h e i m p u r i t y f l u o r e s c e n c e , s i n c e a t t h e c o n c e n t r a t i o n s f o r maximum t r a n s f e r t h e r e i s o n l y one i m p u r i t y m o l e c u l e i n about t e n thousand m a t r i x m o l e c u l e s , and t h e a b s o r b t i o n by t h e i m p u r i t y m o l e c u l e s would be v e r y s m a l l . T h i s p r o c e s s was d i s c u s s e d i n g r e a t e r d e t a i l by p Bowen , and r e j e c t e d as a p o s s i b l e e x p l a n a t i o n o f t h e 25 t r a n s f e r p r o c e s s . 2. The p r o c e s s might be e x p l a i n e d by t h e movement o f an e l e c t r o n and a p o s i t i v e h o l e t h r o u g h t h e l a t t i c e o f the c r y s t a l , w h i c h recombine i n the i m p u r i t y m o l e c u l e t o produce f l u o r e s c e n c e c h a r a c t e r i s t i c o f t h e i m p u r i t y . Such a p r o c e s s o c c u r s i n c e r t a i n i n o r g a n i c m i x t u r e s , f o r example i n ZnS phosphors a c t i v a t e d w i t h a m e t a l , and i n c e r t a i n pure i n o r g a n i c c r y s t a l s , f o r example NaCl w h i c h has been a c t i v a t e d by X - r a d i a t i o n . T h i s p r o c e s s , however, i s i n v a r i a b l y a s s o c i a t e d w i t h o t h e r s w h i c h have no a n a l o g y i n t h e o r g a n i c m i x t u r e s i n v e s t i g a t e d . The ZnS phosphors e x h i b i t no f l u o r e s c e n c e i n t h e pure s t a t e , w h i l e t h e anthracene and na p h t h a l e n e m a t r i c e s o f t h i s experiment e x h i b i t a v i g o u r o u s f l u o r e s c e n c e o f t h e i r own. I n pure i n o r g a n i c c r y s t a l s s uch as Na C l p h o t o c o n d u c t i v i t y and thermoluminescence o c c u r , and t h e s e phenomena a r e e v i d e n c e used t o s u p p o r t t h e arguments i n f a v o u r o f t h e pr e s e n c e o f an e l e c t r o n and a p o s i t i v e h o l e . P h o t o c o n d u c t i v i t y o f t h e type encountered i n i n o r g a n i c c r y s t a l s does n o t o c c u r i n c r y s t a l s o f anthracene and n a p h t h a l e n e , and thermoluminescence has not been r e p o r t e d . F i n a l l y , t h e t r a n s f e r o f energy by means o f t h e movement o f an e l e c t r o n and a p o s i t i v e h o l e t h r o u g h the l a t t i c e i s much s l o w e r t h a n the t r a n s f e r o f energy i n the mixed o r g a n i c c r y s t a l s s t u d i e d . When c r y s t a l s o f a c t i v a t e d ZnS a r e i r r a d i a t e d w i t h gamma-rays t h e d u r a t i o n -3 o f the l i g h t p u l s e s produced i s o f the o r d e r o f 10 seconds, w h i l e t h e d u r a t i o n o f p u l s e s from a n t h r a c e n e o r na p h t h a l e n e is of the order of 10 seconds. I f the pulses of l ight produced in-an anthracene crystal are detected by means of a photomultiplier tube and the amplified e lectr ica l pulses are viewed on the screen of a fast oscilloscope, these pulses are of the same duration as those produced i n the same manner by a crystal of. anthracene with added ^ naphthacene. From the foregoing evidence i t may.be concluded energy that the transfer of excitation/!by .means of an electron and a positive hole moving through the crystal l a t t ice i s highly improbable in the organic crystals which are the subject of this research. 3. The transfer process may be explained i f the matrix and impurity are assumed to form a sort of conducting system. The orbitals of the outer electrons of atoms in 9. 10 benzene ring compounds are known to overlap . I f in the solid state the orbitals of the outer electrons of adjacent molecules overlap, then i t would be possible for excitation energy absorbed by any particular molecule to be passed along to other molecules by a process analogous to the flow of an electric current by the displacement of electrons. F inal ly the energy would be dissipated by radiation. This flow or transfer of excitation energy could take place whether or not an impurity were present, but i f an impurity, were present i t would be possible for the electron orbitals of the impurity molecule to overlap with the orbitals of the adjacent matrix molecules. Hence the impurity molecules . would be able to accept energy from the matrix molecules 27 v e r y e f f i c i e n t l y * As the c o n c e n t r a t i o n o f i m p u r i t y m o l e c u l e s i s i n c r e a s e d t h e p r o b a b i l i t y o f t h e e x c i t a t i o n energy b e i n g t r a n s f e r r e d t o the i m p u r i t y m o l e c u l e s would be i n c r e a s e d , u n t i l a t a c e r t a i n c o n c e n t r a t i o n a maximum o f e x c i t a t i o n energy i s t r a n s f e r r e d t o the i m p u r i t y m o l e c u l e s . When t h e c o n c e n t r a t i o n passes beyond t h a t n e c e s s a r y f o r maximum t r a n s f e r the i m p u r i t y m o l e c u l e s , i t i s assumed, would remove a g r e a t e r p r o p o r t i o n o f e x c i t a t i o n energy as heat t h a n do the m a t r i x m o l e c u l e s . Hence t h e t r a n s f e r p r o c e s s would become l e s s e f f i c i e n t and the l i g h t o u t p u t o f t h e c r y s t a l as a whole, and o f t h e i m p u r i t y m o l e c u l e s i n p a r t i c u l a r would become s m a l l e r . T h i s t r a n s f e r p r o c e s s , t h e n , e x p l a i n s s a t i s f a c t o r i l y t h e h i g h e f f i c i e n c y o f t r a n s f e r found e x p e r i m e n t a l l y , and a l s o t h e v a r i a t i o n o f t r a n s f e r w i t h i m p u r i t y c o n c e n t r a t i o n as shown i n P l a t e s - V I I I t o X I I . The absence o f t h e p r o c e s s i n l i q u i d and g e l a t i n s o l u t i o n s o f anthracene p l u s naphthacene i s a l s o e x p l a i n e d by t h i s p r o c e s s , i f i t i s assumed t h a t t h e o v e r l a p o f t h e o r b i t a l s i n t h e s e s o l u t i o n s i s much s m a l l e r t h a n t h e o v e r l a p i n the s o l i d s t a t e . The i n t e r a c t i o n o f t h e i m p u r i t y m o l e c u l e e l e c t r o n o r b i t a l s w i t h the m a t r i x o r b i t a l s s h o u l d l e a d t o a s h i f t o f the e l e c t r o n i c energy l e v e l s o f b o t h m a t r i x and i m p u r i t y . Such a s h i f t i s i l l u s t r a t e d by t h e h y p o t h e t i c a l energy l e v e l d i a g r a m shown i n P l a t e X I I I . I n t h e d i a g r a m t h e m a t r i x l e v e l s A a r e s h i f t e d t o l o w e r e n e r g i e s A» and the i m p u r i t y l e v e l s B a r e s h i f t e d t o h i g h e r l e v e l s B T when t h e m a t r i x 28 B B B / B' B* B' o cc UJ UJ 4 IMPURITY MIXTURE MATRIX P l a t e X I I I . H y p o t h e t i c a l energy l e v e l d i a g r a m f o r an o r g a n i c m a t r i x w i t h an added i m p u r i t y . 2? and i m p u r i t y a r e combined i n a s o l i d s o l u t i o n . The s h i f t o f th e m a t r i x l e v e l s i s much s m a l l e r t h a n t h e s h i f t o f t h e i m p u r i t y l e v e l s , because t h e i n t e r a c t i o n o f a g i v e n m a t r i x m o l e c u l e w i t h i m p u r i t y m o l e c u l e s i s much l e s s t h a n t h e i n t e r a c t i o n o f an i m p u r i t y m o l e c u l e w i t h t h e s u r r o u n d i n g m a t r i x m o l e c u l e s . When t h e i m p u r i t y i s d i s s o l v e d i n d i f f e r e n t m a t r i c e s t h e s h i f t i n energy l e v e l s BB» w i l l depend on t h e i n t e r a c t i o n w i t h the m a t r i x , and t h e f l u o r e s c e n c e o f t h e i m p u r i t y w i l l appear a t d i f f e r e n t w a v e l e n g t h s . T h i s e x p l a i n s t h e d i f f e r e n c e i n wav e l e n g t h s o f t h e naphthacene bands i n ant h r a c e n e and na p h t h a l e n e ( T a b l e I ) . When t h e m a t r i x i s e x c i t e d the t r a n s i t i o n GA' t a k e s p l a c e . The r a d i a t i o n l e s s t r a n s i t i o n A TB* t h e n t a k e s p l a c e by t r a n s f e r o f energy and d i s s i p a t i o n o f energy as h e a t : a t t h e same t i m e t h e t r a n s i t i o n A'G o c c u r s , and t h e r e l a t i v e numbers o f t h e s e t r a n s i t i o n s w i l l depend upon t h e c o n c e n t r a t i o n o f t h e i m p u r i t y . F i n a l l y t h e t r a n s i t i o n B TG t a k e s p l a c e . The s u p e r i o r e f f i c i e n c y o f t h e t r a n s f e r i n the c r y s t a l s o f a n t h r a c e n e w i t h added naphthacene may be e x p l a i n e d w i t h t h e a i d o f P l a t e X I I I , because the i n t e r v a l A'B* i s much s m a l l e r f o r t h i s m i x t u r e t h a n f o r t h e o t h e r m i x t u r e s i n v e s t i g a t e d . IV. APPENDICES I . RESULTS OE OTHER AUTHORS AND RESULTS OF PRESENT EXPERIMENT T a b l e I I . R e s u l t s o f o t h e r a u t h o r s Compound ; C o n d i t i o n o f compound i Source o f E x c i t a t i o n Wavelengths o f Bands A 0 A u t h o r Naphthalene S o l i d X - r a y s 3430 W r i t e r UV# 5385, 3 4 3 0 , 3490 B u r d e t t and 6 Jones L i q u i d s o l n . o f e t h e r , i s o p e n t a n e , and a l c o h o l a t -180 °C. UV 3355, 5400, 3475, 3 5 2 0 , 3 5 7 5 , 3650 R e i d 1 1 A n t h r a c e n e S o l i d i X - r a y s 4475, 4 7 1 0 , 5040 W r i t e r UV 4040, 4220, 4460, 4690 W r i t e r UV 4000, 4200, 4400, 4 7 0 0 , 4950 Kortum and F i n c k h 1 2 G-amma-rays, d e u t e r o n s , X-rays 4240, 4440, 4700 R o t h 1 5 # U l t r a - v i o l e t l i g h t T a b l e I I . ( C o n t i n u e d ) Compound ; C o n d i t i o n o f compound! Source o f E x c i t a t i o n ! Wavelengths o f Bands A-° A u t h o r Anthracene S o l i d j • uv# 14030, 4220, 4380, 4450 ' G a n g u l e y ^ uv '4025, 4220, 4450, 4735, 5090 15 P r i n g s h e i m L i q u i d s o l n . i n benzene uy ;3828, 4042,' 4280, 4547 • and ;Sambursky W o l f s o n 16 uv •3855, 4065, 4285, 4565, 4870 15 P r i n g s h e i m , ; L i q u i d s o l n . i n a l c o h o l uv ,3790, 4000, 4240, 4500 14 | Ganguley , ; S o l i d s o l n . i n n a p h t h a l ene UV '3965, 4140^ 4395, 4680 15 P r i n g s h e i m Naphthacene I ' i ; i S o l i d s o l u t i o n i n anthrac ene X - r a y s 5035, 5320, 5735 W r i t e r UV 4980, 5330, 5740 n -, 14 Ganguley S o l i d s o l n . i n n a p h t h a l e ne X-rays 4965, 5285, 5680 W r i t er . L i q u i d s o l n . i n e t h e r , ; i s o p e n t a n e , and a l c o h o l a t -180 °C. and 20 °C. ! UV 4780, 5130, 5400 4730, 5070, 5450 R e i d ' L i q u i d s o l n . i n a l c o h o l UV 4750, 5080, 5460 14 Ganguley 1 , 2,5,6-di-b e n z a n t h r a -cene ; S o l i d s o l n . i n n a p h t h a l ene X - r a y s '3520, 3720, 4080, 4250, 4690, 5040 W r i t e r L i q u i d s o l n . . i n e t h e r , i s o p e n t a n e and a l c o h o l ! a t -180 °C. ! _.. ... J UV i 3950, 4080, 4180, 43IO, 4440 11 R e i d 1 # U l t r a - v i o l e t l i g h t 32 T a b l e I I I . Wavelengths and r e l a t i v e i n t e n s i t i e s o f bands i n i c r y s t a l s o f nap h t h a l e n e w i t h added 1 , 2 , 5 , 6 - d i b e n z a n t h r a c e n e _> C o n c e n t r a t i o n Wavelength o f maxima o f bands - A° Moles 1,2,5,6- 3410 3520 3720 4080 4250 4690 5040 p e r mole naphthalene R e l a t i v e i n t e n s i t i e s o f bands A r b i t r a r y u n i t s 0 5000 4.14 X 10~6 5000 99.3 45.9 15.6 7.28 9.45 X 10"6 5000 142 1.99 X io-* 5000 174 no 50.0 22.1 2.77 X io-5 5000 295 224 68.8 28.6 3.23 X lo"* 5000 412 250 88.5' 50.0 4.61 X 10-5 5000 X , 481 364 242 116 5.?53 X lo"* 5000 740 856 880 459 1.01 X io" 4 5000 2650 1280 5560 ; 7970: 2620 1460 1.39 X i o " 4 5000 977 1140 768 388 2.21 X lo" 4 i 5000 509 277 199 Band a t t r i b u t e d t o n a p h t h a l e n e 1,2,5 , 6-dibenzanthracene 33 Table IV. Wavelengths and r e l a t i v e i n t e n s i t i e s o f bands i n c r y s t a l s o f na p h t h a l e n e w i t h added naphthacene C o n c e n t r a t i o n Wavelengths o f maxima'of bands - A° Moles naphthacene per mole naphthalene 3 4 1 5 ' 4 9 6 5 5 2 8 5 5 6 8 0 R e l a t i v e i n t e n s i t i e s o f bands A r b i t r a r y u n i t s 0 5 0 0 0 5 . 6 2 x l O " ? 5 0 0 0 1 6 4 1 3 9 3 6 . 7 -G 5 . 6 7 x 1 0 • 5 0 0 0 616 8 6 0 263 1 . 4 7 x 1 0 " 5 5 0 0 0 565 1 0 5 0 3 5 4 3 . 3 8 x 1 0 ~ 5 5 0 0 0 927 2 1 7 5 8 8 0 5 . 6 7 x 1 0 ~ 5 5 0 0 0 7 5 8 1 8 1 5 9 2 9 8 . 4 3 x 1 0 " - 5 5 0 0 0 667 . 1 4 5 0 1 0 2 0 1 . 2 8 x 1 0 " 4 5 0 0 0 5 1 5 1145 9 2 7 1 . 7 0 x 1 0 " 4 5 0 0 0 422 912 1 0 2 0 Band a t t r i b u t e d t o Naphthalene Naphthacene I 34 Table V. Wavelengths and r e l a t i v e i n t e n s i t i e s of bands i n c r y s t a l s of anthracene w i t h added naphthacene Concentration Wavelengths of maxima of b ands - A 0 Moles naphtha-cene per mole anthrac ene 4 4 4 5 4 7 1 0 5 0 4 0 ( ? ; 5 0 3 5 5 3 2 0 5 7 3 5 R e l a t i v e i n t e n s i t i e s of bands Arbitra3?y u n i t s 0 5 0 0 0 1 7 4 0 ' 3 4 8 8 . 6 8 x 1 0 " 7 5 0 0 0 1 4 6 0 1 7 8 0 1390 3 8 0 7 . 6 6 x 1 0 ~ 6 5 0 0 0 1 2 1 0 4 6 3 0 6190 1 6 1 5 2.24 x 1 0 " - 5 5 0 0 0 1 8 7 0 4 6 7 5 7 4 8 0 2 5 2 0 8.29 x 1 0 " 5 5 0 0 0 1425 1 6 , 7 0 0 4 3 , 0 0 0 1 0 , 0 0 0 1.04 x 1 0 ~ 4 5 0 0 0 1 1 7 , 0 0 0 4 5 4 , 0 0 0 1 2 8 , 5 0 0 1 . 6 9 x 1 0 " 4 ; 5 0 0 0 j.. 1. , 5 1 3 , 0 0 0 2 5 2 , 0 0 0 2 . 9 3 x 1 0 " 4 ! 5 0 0 0 1 , 7 4 0 , 0 0 0 5 1 6 , 0 0 0 4 . 7 1 x 10*" v ! 5 0 0 0 789 ,ooo 249 ,000 9.34 x 1 0 ~ 4 5 0 0 0 59,800 2 0 3 , 5 0 0 6 7 , 2 0 0 Band a t t r i b u t e d t o Anthrac ene Naphthacene 35 I I . THE GROWTH OF SINGLE ORGANIC CRYSTALS The growth of single crystals of organic materials such as anthracene and naphthalene was undertaken for two reasons. The increasing use of s c in t i l l a t ion counters in nuclear physics made i t desirable to grow such crystals for use in the Department of Physics and for studying their properties when used in a s c in t i l l a t ion counter. Secondly, the growth of the crystals with added impurities would fac i l i ta te the studies being made of the transfer of energy. The lat ter investigation, of course, might lead to tb.e discovery of improved crystals for use in s c in t i l l a t i on counters. Many methods have been described for the growth of single crystals of various materials. Each of these methods is usually best suited to a certain class of substances. For example, crystals of high melting point compounds such as CaWO^ may be grown by blowing the powdered compound across a flame, or Rochelle salts may be grown by slow cooling from a supersaturated solution. Obviously neither of these methods i s suitable for anthracene or naphthalene. Huber and his colleagues 1^ have described a method of growing single crystals of anthracene.. In this method a container f i l l e d with anthracene is placed in a silvered enclosure in a furnace, and the furnace is cooled at the rate of about 1 ° C . per hour. The crystal starts growing from the bottom of the c o n t a i n e r and the growth proceeds v e r t i c a l l y . Huber's reas o n s f o r u s i n g t h i s arrangement a r e not c l e a r l y 18 e x p l a i n e d . S t o c k b a r g e r has d e s c r i b e d a method f o r growing s i n g l e c r y s t a l s o f L i F w h i c h t h e a u t h o r has adapted f o r t h e p r o d u c t i o n o f o r g a n i c s i n g l e c r y s t a l s . I n S t o c k b a r g e r ' s method a c o n t a i n e r f i l l e d w i t h L i F was s l o w l y l o w e r e d t h r o u g h two f u r n a c e s s e p e r a t e d by a p l a t i n u m b a f f l e . The f u r n a c e s were kept a t d i f f e r e n t t e m p e r a t u r e s so t h a t a l a r g e t e m p e r a t u r e g r a d i e n t e x i s t e d between them, i n w h i c h f r e e z i n g o f t h e m o l t e n s a l t t o o k p l a c e . I n b o t h t h e above methods th e shape o f the c o n t a i n e r i s o f i m p o r t a n c e , and the c r y s t a l l i z a t i o n proceeds i n a p l a n e . The method employed t o grow th e c r y s t a l s , t h e n , was t o l o w e r s l o w l y a s p e c i a l l y shaped c o n t a i n e r f u l l o f th e m o l t e n compound t h r o u g h a s h a r p t e m p e r a t u r e g r a d i e n t i n w h i c h f r e e z i n g t o o k p l a c e . When t h i s method i s used i t i s i m p o r t a n t t o o b t a i n c e r t a i n c o n d i t i o n s i n o r d e r t o ensure c o r r e c t g r o w t h : t h e c o n t a i n e r must be shaped so as t o s t a r t t h e growth o f t h e c r y s t a l p r o p e r l y ; t h e i s o t h e r m a l s i n the f u r n a c e must be h o r i z o n t a l so t h a t t h e growth o f t h e c r y s t a l w i l l p r o c e e d v e r t i c a l l y ; and the temperature g r a d i e n t must be as l a r g e as p o s s i b l e so t h a t t h e heat o f f o r m a t i o n o f t h e c r y s t a l w i l l be r a p i d l y conducted away, l e a v i n g t h e i s o t h e r m a l s u n d i s t u r b e d . The shapes o f s e v e r a l t y p e s o f c o n t a i n e r s a r e shown i n P l a t e XIV. I n P l a t e XIV c o n t a i n e r A i s o f t h e t y p e used by Ruber and h i s a s s o c i a t e s , t y p e B i s t h a t used by 37 B P l a t e XIV. C o n t a i n e r s f o r the growth o f c r y s t a l s 38 S t o c k b a r g e r , and t y p e s C and D were employed by t h e a u t h o r . A l l shapes were t r i e d by t h e a u t h o r , who found t y p e D t o be t h e most s u c c e s s f u l f o r t h e growth o f anthracene and n a p h t h a l e n e c r y s t a l s . S e v e r a l f u r n a c e s were employed by t h e a u t h o r . The f i r s t was a t hand when t h e r e s e a r c h began. One p e r f e c t c r y s t a l o f n a p h t h a l e n e was grown i n t h i s furnace,- but i t c o u l d not be d u p l i c a t e d . Two f u r n a c e s were s u b s e q u e n t l y d e s i g n e d and c o n s t r u c t e d . These were t e s t e d and a l t e r e d so t h a t c o n s i s t e n t l y good r e s u l t s were f i n a l l y o b t a i n e d w i t h t h e f u r n a c e shown s c h e m a t i c a l l y i n P l a t e XV. The h e a t i n g element i n t h i s f u r n a c e i s p l a c e d a t t h e t o p so t h a t h o r i z o n t a l i s o t h e r m a l s may o b t a i n i n . t h e f u r n a c e . The s t e e l t u b i n g was c u t assshown and i n s u l a t i o n o m i t t e d from t h e bottom s e c t i o n o f t h e f u r n a c e i n o r d e r t o produce t h e h i g h e s t p o s s i b l e t e m p e r a t u r e g r a d i e n t a c r o s s t h e gap. The t e m p e r a t u r e s o f t h e thermocouples f o r d i f f e r e n t h e a t e r v o l t a g e s a r e shown i n P l a t e X V I . Assuming t h a t t h e g r e a t e s t p a r t o f t h e t e m p e r a t u r e drop t a k e s p l a c e a c r o s s t h e gap t h e temperature g r a d i e n t w i l l be seen t o be o f t h e o r d e r o f 200 t o 1000 °C. p e r i n c h a c r o s s t h e gap, depending on t h e h e a t e r v o l t a g e . The c o n t a i n e r s were s u p p o r t e d i n t h e f u r n a c e by means o f a f i n e w i r e passed t h r o u g h t h e copper t u b i n g . The w i r e was wound around a wheel w h i c h r e p l a c e d the hour hand of a c l o c k . The c o n t a i n e r was l o w e r e d m e r e l y by o p e r a t i n g the c l o c k . Rates o f d e s c e n t v a r y i n g f r o m .06.5 t o .26 i n c h e s 59 i 8 O.D. COPPER TUBING ROCK WOOL INSULATION HEATING ELEMENT ALUMINUM PLATE STEEL TUBING 3" 3" 2 T t.D. X 3 4 O.D. ROCK WOOL INSULATION COPPER-CONSTANTIN THERMOCOUPLE r 4 TRANSITE 12 DIAM. FURNACE SMOKE PIPE P l a t e XV. Arrangement o f f u r n a c e f o r the growth o f c r y s t a l s , 40 3 0 0 r -3 0 4 0 5 0 H E A T E R V O L T A G E 70 P l a t e XVI. Temperatures o f thermocouples i n f u r n a c e of P l a t e XV. 41 p e r hourwere r e a d i l y o b t a i n e d by u s i n g wheels o f d i f f e r e n t d i a m e t e r s . The f u r n a c e s were p l a c e d i n a c o n s t a n t i _ p tempe r a t u r e chamber i n o r d e r t o o b v i a t e d a i l y v a r i a t i o n s i n room t e m p e r a t u r e , and power f o r the h e a t e r s was s u p p l i e d by a c o n s t a n t v o l t a g e t r a n s f o r m e r . C r y s t a l s w i t h d i a m e t e r s o f l / 2 i n . , § i n . , and 2 i n . were grown. Those o f 1/2 , i n . diam. were s t i k i n g l y s u p e r i o r t o t h e r e s t , many b e i n g p e r f e c t . However, 1 i n . diam. i n g o t s o f n a p h t h a l e n e w h i c h c o n s i s t e d o f two o r t h r e e p i e c e s , and a 2 i n . diam. i n g o t o f a n t h r a c e n e were grown. The l a t t e r gave s a t i s f a c t o r y performance when used i n a s c i n t i l l a t i o n c o u n t e r . I t i s b e l i e v e d t h a t f u r n a c e s o f l a r g e r i n s i d e d i a m e t e r would be r e q u i r e d t o grow p e r f e c t s i n g l e c r y s t a l s o f d i a m e t e r s l a r g e r t h a n l / 2 i n . I n such f u r n a c e s t h e d i s t o r t i o n o f the i s o t h e r m a l s by the c o n t a i n e r would be c o n s i d e r a b l y l e s s t h a n i n t h e f u r n a c e s o f 2f i n . i n s i d e diam., and the c o n d i t i o n s f o r c r y s t a l growth would thus be much s u p e r i o r f o r l a r g e c r y s t a l s . 42 BIBLIOGRAPHY 1. S. C. Ganguley, J . C. P. 2JL» 128 (1945). 2. E. J . Bowen, Nature 159. 706 (1947). 3. T. F o r s t e r , Z. E l e k t r o c h e m . £5. , 93 (1949). 4. H. K a l l m a n n , M. F u r s t , P. R. Jit 8 5 7 (1950).. 5. R. W. Engstrom, J . 0. S. A. 57, 420 (1 9 4 7 ) . 6. R. A. B u r d e t t , L. C. J o n e s , J r . , J . 0. S. A. 534 (1947). 7.. E. Jahnke, F. Emde, F u h k t i o n o n t a f e l n m i t Formeln und K u r v e n , New Y o r k , Dover, 1943. 8. G. F. J . G a r l i c k , Luminescent M a t e r i a l s , Chapter I I , O x f o r d , The C l a r e n d o n P r e s s , 1949. 9. J . P i a t t , R eport f o r P e r i o d J u n e l . 1949 t o March 31. 1950. P h y s i c s Department, S p e c t r o s c o p y L a b o r a t o r y , U n i v e r s i t y of Chi c a g o . 10. H. Sponer, E. T e l l e r , R. M. P. 1J5., 76 (1941). 11. C. R e i d , P r i v a t e Communication, Vancouver. 12. G. Kortum, A. F i n c k h , Z. P. C. B 52. 263 (1942). 13. L. Ro t h , P. R. 21t 983 (1949). 14. S. C. Ganguley, N a t u r e 153. 652 ( 1 9 4 4 ) . 15. P. P r i n g s h e i m , T r a n s . F a r . Soc. 28 (1939). 16. S. Sambursky, J . W o l f s o n , T r a n s . F a r . Soc. £6. , 427 (1940). 17. 0. Huber, F. Humble, H. S c h n e i d e r , R. S t e f f e n , H e l v . Phy. A c t a 22., 4l8 (1949). 18. D. C. S t o c k b a r g e r , R. S. I . 2, 133 (1936). 

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