Spectroscopic Characterization of Minerals and Their Surfaces

Chapter 13 What

Excites

Triboluminescence?

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on August 20, 2015 | http://pubs.acs.org Publication Date: November 29, 1990 | doi: 10.1021/bk-1990-0415.ch013

Linda M. Sweeting Department of Chemistry, Towson State University, Baltimore, MD 21204 We have examined the spectra emitted by triboluminescent materials which are also photoluminescent and attempted to correlate their crystal structures with their triboluminescence (fractoluminescence). The spectra reveal that the primary event i s charge separation followed by a discharge (lightning); the UV-vis emission of the discharge i s absorbed and excites the photoluminescence of the material. Although a noncentric crystallographic space group resulting i n macroscopic piezoelectricity i s common i n triboluminescent materials, it i s neither necessary nor sufficient for triboluminescence to occur: disorder and impurities may also provide a structural basis for triboluminescence. Triboluminescence, from the Greek word tribein (to rub) i s a term used to describe the visible (and UV) emissions of materials when they are stressed to failure. This phenomenon i s very common among minerals (see Table I ) , and is well known to spelunkers who enjoy smashing fluorite deposits to see the l i g h t . Earthquake lights (1) (2) are probably triboluminescence on a grand scale. The term triboluminescence is often used to describe any light emission occurring upon impact with or grinding of a crystalline material, and is certainly more than one phenomenon (3,). Light emissions caused by heating during fracture, such as thermoluminescence and blackbody radiation, are common, but neither they nor chemical reactions such as oxidation are s t r i c t l y considered triboluminescence; they w i l l not be discussed i n this paper. Triboluminescence is sometimes observed during deformation even without fracture. Salts such as zinc sulfide (4) (5) and sodium chloride (6) (7) which have been doped either by photoluminescent ions or by gamma irradiation have been shown to emit light under elastic or plastic deformation. The emission i s thought to be produced by the recombination of defects of opposite charge which migrate and recombine during strain of the crystal. Eckhardt has also observed that some piezoelectric crystals w i l l emit light when compressed or stretched without fracture (8). This form of triboluminescence w i l l be referred to as deformation luminescence. 0097-6156/90/D415-0245$06.00/0 e 1990 American Chemical Society

In Spectroscopic Characterization of Minerals and Their Surfaces; Coyne, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1990.

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Table I . Triboluminescent M i n e r a l s


a) F r a c t o l u m i n e s c e n t l i t h i u m f l u o r i d e (1) sodium n i t r a t e (2) sodium s u l f a t e (3) potassium n i t r a t e (2) magnesium o x i d e (4) magnesium s u l f a t e (3) a r a g o n i t e (CaC0 ) (5) c a l c i t e (CaC0 ) ( I c e l a n d ) (6) (7) marble (CaC0 ), Y u l e (8) d o l o m i t e (CaMg(C0 ) ) (9) f l u o r i t e (CaF ) (5) (7) (10) ( 1 1 ) , doped (12) c a l c i u m o x i d e (4) b a s a l t , T a b l e M o u n t a i n ( C a ( P 0 ) / e t c ) (8) h y d r o x y a p a t i t e (human bone Ca (P0 ) 0H) (13) (14) a p a t i t e ( p h o s p h o r i t e ) C a ( P 0 ) F (5) gypsum ( s e l e n i t e ) (CaS0 .2H 0) (3) w a l l a s t o n i t e ( C a S i 0 ) (11) c e l e s t i t e (SrS0 ) (3) (5) w i t h e r i t e (BaC0 ) (5) barium c h l o r i d e (11) b a r i t e (BaS0 ) (3) (5) 3

3

3

3

2

2

3

4

5

5

4

4

2

4

3

3

2

3

4

3

4

c r y o l i t e (Na AlF ) (5) 3

6

q u a r t z ( S i 0 ) ( 5 ) (6) (7) (11) (15) s i l i c a g l a s s ( S i 0 ) ( 6 ) , f u s e d q u a r t z (16) c h a l c e d o n y , amorphous ( S i 0 ) (6) c l a y s , on s o l v a t i o n , m o n t o m o r i l l o n i t e ( A l ( S i 0 ) (0H) ) , k a o l i n ( A l ( S i 0 ) ( 0 H ) ) (17) g r a n i t e , S a l i d a ( S i 0 / A l 0 / e t c . (8) (18) mica ( K S i 0 ? ) (5) k u n z i t e ( L i A l S i 0 w i t h Mn) (11) 2

2

2

4

4

4

1 0

2

2

2

4

1 0

4

8

2

3

5

2

e

a r s e n o l i t e from H C l ( A s 0 ) c l a u d e t i t e (As 0 ) (20) s t i b n i t e (Sb S ) (5) 2

2

2

3

(5) (19)

3

3

r u t i l e ( T i 0 ) (5) manganous s u l f a t e (3) i r o n (21) copper ( I I ) s u l f a t e p e n t a h y d r a t e (3) w i l l e m i t e ( Z n S i 0 ) (6) s p h a l e r i t e , z i n c b l e n d e (ZnS) (5) (6) (11) 2

2

4

Continued on next page



247

What Excites Triboluminescence?

13. SWEETING

Table I. Continued b) Luminescent on D e f o r m a t i o n o r Showing B l a c k Body l i t h i u m f l u o r i d e (22) (23) (24) sodium c h l o r i d e (5) (6) ( 2 5 ) , X - i r r a d i a t e d sodium f l u o r i d e (22) p o t a s s i u m c h l o r i d e (23) (27) p o t a s s i u m f l u o r i d e (27)

Radiation

(26) (27)

c a l c i t e (6) (7) a p a t i t e (6) gypsum (CaS0 ) w i t h manganese (11) f l u o r i t e ( C a F ) ( 5 ) (7) w i t h r a r e e a r t h s (11) t r e m o l i t e (a calcium s i l i c a t e ) ( 1 1 ) 4

2

q u a r t z ( S i 0 ) (5) (6) (11) (15) (28) f u s e d q u a r t z (16) s i l i c a g l a s s (29) t o u r m a l i n e (an a l u m i n o s i l i c a t e w i t h B) (11) f e l d s p a r (an a l u m i n o s i l i c a t e w i t h K, Na, Ca) (6) 2

z i n c o x i d e , doped (30) z i n c s u l f i d e , doped (27) (31)

Continued on next page

American Chemical Society Library 1155 18th St., N.W. In Spectroscopic Characterization of Minerals and Their Surfaces; Coyne, L., et al.; ACS Symposium Series; American D.C. Chemical Society: Washington, DC, 1990. Washington, 20036

248

SPECTROSCOPIC CHARACTERIZATION OF MINERALS AND THEIR SURFACES Table I. Continued. Footnotes to Table I.


1.

B e l y a e v , L. M.; M a r t y s h e v , Yu. N. phvs. s t a t . s o l . 1969, 34, 5762. 2. Chandra, B. P.; Z i n k , J . I . J . Phvs. Chem. S o l i d s . 1981, 42, 529532. 3. Chandra, B. P.; Z i n k , J . I . I n o r p . Chem. 1980, 19, 3098-3102. 4. W i l l i a m s , G. P. J r . ; T u r n e r , T. J . S o l . S t a t e Commun. 1979, 29. 201-203. 5. W o l f f , G.; G r o s s , G.; S t r a n s k i . I . Ν. Z. E l e k t r o c h e m i e . 1952, 56. 420-428. 6. Wick, F. G. J . Opt. Soc. Amer. 1937, 27, 275-285. 7. Chapman, G. N. ; W a l t o n , A. J . PACT ( R i x e n s a r t . B e l g i u m ) . 1982, 6, 533-538. 8. C r e s s , G. 0.; Brady, B. T.; R o w e l l , G. A. Geophvs. Res. L e t t . 1987, 14, 331-334. 9. W a l t o n , A. J . Adv. Phvs. 1977, 26, 887-948. 10. Longchambon, H. C. R. Hebdom. Seances Acad. S c i . P a r i s . 1923, 176. 691-693. 11. Wick, F. G. J . Ont. Soc. Amer. 1939, 29, 407-412. 12. Chapman, G. N. ; W a l t o n , A. J . J . Phvs. C S o l . S t a t e . 1983, 16, 5543-5551. 13. K r a u y a , U. E. ; K n e t s , I . V.; L a i z a n , V. B. Mekh. P o l i m e r o v . 1977, 4, 746-749. 14. D i s s o l u t i o n o f i n o r g a n i c s from t h e bone l e a v e s t h e t r i b o l u m i nescence i n t a c t ; , d i s s o l u t i o n o f t h e o r g a n i c m a t e r i a l d e s t r o y s t h e t r i b o l u m i n e s c e n c e . M e i r Lahav, p e r s o n a l communication. 15. Chapman, G. N.; W a l t o n , A. J . J . A P P I . Phvs. 1983, 54, 5961-5965. 16. Kondo, K. ; A h r e n s , T. J . ; Sawaoka, A. J . A P P I . Phvs. 1983, 54, 4382-4385. 17. Coyne, L. M.; Lahav, N.; L a w l e s s , J . G. N a t u r e . 1981, 292, 819 821. Lahav, N. ; Coyne, L. M. ; L a w l e s s , J . G. C l a y s C l a y M i n e r . 1982, 30, 73-75. 18. Brady, B. T.; R o w e l l , G. A. N a t u r e . 1986, 321, 488-492. 19. T r a u t z , Μ., Z. Phvs. Chem. 1905, 53, 1-63. 20. S t r a n s k i , I . N. ; S t r a u s s , E. ; W o l f f , G. Z. E l e k t r o c h e m i e . 1955, 59, 341-350; 1951, 55, 633-636. 21. Ohlman, Y. P h v s i c a S c r i o t a . 1979, 20, 620-622. 22. L i n k e , E. S i t z . Acad. Wissen. 1981, 3N, 105-113. 23. Meyer, K.; P o l l y , F. phvs. s t a t . s o l . 1965, 8, 441-456. 24. Hoffman, K.; L i n k e , E. K r i s t . T e c h n i k . 1976, 11, 835-845; 1977, 12, 495-503. 25. F r o h l i c h , F.; S e i f e r t , P. C r y s t a l L a t t i c e D e f e c t s . 1971, 2, 239242. 26. P i r o g , M.; S u j a k , B. A c t a Phvs. P o l o n . 1968, 33, 863-873. 27. A l z e t t a , G.; Chudacek, I . ; Scarmozzino, R. phvs. s t a t . s o l . 1970, 1, 775-785. 28. Zubov, V. G.; Zakharova, Ε. K.; O s i p o v a , L. P. V e s t . Mosk. U n i v . F i z . 1975, 30, 366-367. 29. Z i n k , J . I . ; Beese, W.; S c h i n d l e r , J . W.; S m i e l , A. J . AppI. Phys. L e t t . 1982, 40, 110-112. S m i e l , A. T.; F i s h e r , T. A. A P P I . Phvs. L e t t . 1982, 4 1 , 324-326. 30. Bhushan, S.; A s a r e , R. P. Czech. J . Phvs. 1981, B31, 913-916. 31. T h i e s s e n , P. Α.; Meyer, K. N a t u r w i s s e n s c h a f t e n . 1970, 57, 423-427. Meyer, K.; O b r i k a t , D. Z. Phvs. Chem. 1969, 240, 309-324.


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249


M a t e r i a l s w h i c h emit l i g h t on f r a c t u r e are s a i d t o be f r a c t o l u m i n e s c e n t and may be c l a s s i f i e d by t h e i r e m i s s i o n s p e c t r a . Nonphotoluminescent s o l i d s such as q u a r t z , s u c r o s e and t a r t a r i c a c i d have a t r i b o l u m i n e s c e n c e spectrum i n d i s t i n g u i s h a b l e from the 7r π e m i s s i o n o f d i n i t r o g e n c h a r a c t e r i s t i c o f l i g h t n i n g ( F i g u r e 1) (9) . I t i s c l e a r t h a t charge s e p a r a t i o n i s the p r i m a r y event, f o l l o w e d by e l e c t r o n bombardment o f d i n i t r o g e n i n the a i r n e a r the c h a r g e d (presumably new) s u r f a c e . The e m i s s i o n i s accompanied by the e x p e c t e d r a d i o s i g n a l s , and e l e c t r o n and p o s i t i v e i o n r e l e a s e (10) » and thus w i l l be c a l l e d " l i g h t n i n g " throughout t h i s paper. Most o f the c r y s t a l s i n t h i s group are n o n c e n t r i c and thus p i e z o electric. I n f a c t sucrose has been shown t o emit l i g h t o n l y f o r c l e a v a g e w i t h a component p e r p e n d i c u l a r t o i t s p y r o e l e c t r i c a x i s ( 9 ) . The o b s e r v a t i o n o f l i g h t n i n g p r o v i d e s c l e a r e v i d e n c e f o r charge s e p a r a t i o n and thus good e v i d e n c e f o r f r a c t u r e . F o r p h o t o l u m i n e s c e n t c r y s t a l s , the l i g h t e m i t t e d i s v e r y s i m i l a r t o the f l u o r e s c e n c e o r phosphorescence e m i s s i o n o f the s o l i d , w i t h l i t t l e e v i d e n c e o f the l i g h t n i n g t h a t might i n d i c a t e charge s e p a r a t i o n . F i g u r e 2 g i v e s two examples o f t r i b o p h o t o l u m i nescence s p e c t r a (Photoluminescence s p e c t r a were o b t a i n e d on a P e r k i n Elmer LS5B. T r i b o l u m i n e s c e n c e s p e c t r a were o b t a i n e d on an EG&G PARC 1421 HQ i n t e n s i f i e d diode a r r a y d e t e c t o r w i t h a s s o c i a t e d model 1460 OMA I I I o p t i c a l m u l t i c h a n n e l a n a l y z e r and model 1229 o r 1234 s p e c t r o m e t e r . ) We have f o c u s s e d our r e s e a r c h on t h i s p o o r l y u n d e r s t o o d form o f t r i b o l u m i n e s c e n c e . We propose the f o l l o w i n g mechanism f o r t r i b o p h o t o l u m i n e s c e n c e , o r i g i n a l l y p r o p o s e d by Longchambon (11) and Harvey ( 1 2 ) : 1. B r e a k i n g a t r i b o l u m i n e s c e n t c r y s t a l s e p a r a t e s charge a c r o s s the growing c r a c k o r between s u r f a c e p a t c h e s . 2. Charge can accumulate i f the m a t e r i a l i s p i e z o e l e c t r i c o r i f t h e r e are d e f e c t s i n the c r y s t a l s u f f i c i e n t t o p e r m i t s i g n i f i c a n t charge s e p a r a t i o n . 3. When the v o l t a g e i s g r e a t enough ( 1 3 ) , e l e c t r o n s escape from the s u r f a c e ( e x o e l e c t r o n e m i s s i o n ) and a d i s c h a r g e o c c u r s t h r o u g h the atmosphere near the new s u r f a c e . 11.5 eV i s needed t o e x c i t e the d i n i t r o g e n bands o b s e r v e d from s u c r o s e and o t h e r nonphotoluminescent c r y s t a l s . 4. Gas m o l e c u l e s ( u s u a l l y d i n i t r o g e n ) i n the gap a r e e x c i t e d by e l e c t r o n bombardment. 5. The U V - v i s e m i s s i o n o f the gas ( l i g h t n i n g ) e x c i t e s the m o l e c u l e s o f the c r y s t a l i f they absorb i n t h i s r e g i o n (250 450 nm). 6. The m o l e c u l e s o f the c r y s t a l f l u o r e s c e o r phosphoresce (tribophotoluminescence). The e x c i t a t i o n o f the m o l e c u l e s o f the c r y s t a l c o u l d a l s o o c c u r by e l e c t r o n bombardment, w h i c h would produce s p e c t r a d i f f e r e n t from p h o t o l u m i n e s c e n c e i n some c a s e s . 3

u

3


9

Crystallography To examine the c o r r e l a t i o n between c r y s t a l s t r u c t u r e and t r i b o l u m i nescence we p r e p a r e d and s t u d i e d two s e r i e s o f compounds w i t h some b r i g h t l y t r i b o l u m i n e s c e n t members: 9 - s u b s t i t u t e d a n t h r a c e n e s (14) ( S e r i e s I ) and alkylammonium t e t r a k i s ( d i b e n z o y l m e t h a n a t o ) e u r o p a t e s and o t h e r l a n t h a n a t e s ( S e r i e s I I ) .



250

SPECTROSCOPIC CHARACTERIZATION OF MINERALS AND THEIR SURFACES

F i g u r e 1. T r i b o l u m i n e s c e n c e Spectrum o f S u c r o s e . Spectrum o b t a i n e d w i t h 5, 10 sec a c q u i s i t i o n s and a 25 /im s l i t u s i n g a 142X c h e v r o n d e t e c t o r .


SWEETING



a

300

400

500

λ

600

(nm)

b

300

400

500 λ

600

700

(nm)

F i g u r e 2. T r i b o l u m i n e s c e n c e and P h o t o l u m i n e s c e n c e S p e c t r a . _·_·-_ p h o t o l u m i n e s c e n c e e x c i t a t i o n , photoluminescence emission, triboluminescence. a) 1 - ( 9 - A n t h r y l ) e t h a n o l , t r i b o l u m i n e s c e n c e w i t h 10, 10 sec scans and a 25 μϊΆ s l i t . ( C o p y r i g h t 1988 A m e r i c a n C h e m i c a l Society.) b) Triethylammonium t e t r a k i s ( d i b e n z o y l m e t h a n a t o ) e u r o p a t e , t r i b o l u m i n e s c e n c e w i t h 10, 0.5 sec scans and a 25 μπι s l i t . In Spectroscopic Characterization of Minerals and Their Surfaces; Coyne, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1990.

252

SPECTROSCOPIC CHARACTERIZATION OF MINERALS AND THEIR SURFACES Ar

o-c NR

+ 4

,C

Eu! o—C

R


Series I

/

\Ar

4

Series I I

L i t e r a t u r e r e p o r t s o f c r y s t a l space groups o f t r i b o l u m i n e s c e n t m a t e r i a l s p r o v i d e e v i d e n c e f o r a modest c o r r e l a t i o n between t r i b o l u m i n e s c e n c e and n o n c e n t r i c space group ( 1 5 ) : o f 36 t r i b o l u m i n e s c e n t i n o r g a n i c s u l f a t e s ( 1 6 ) , 21 a r e n o n c e n t r i c and 15 a r e c e n t r i c ; o f 19 t r i b o l u m i n e s c e n t a r o m a t i c o r g a n i c c r y s t a l s (12) o f known c r y s t a l s t r u c t u r e , 13 a r e n o n c e n t r i c and 6 a r e c e n t r i c . Many compounds c r y s t a l l i z e i n more t h a n one space group; t h u s t h e l i t e r a t u r e c r y s t a l s t r u c t u r e s may n o t be r e l e v a n t t o t h e t r i b o l u m i n e s c e n t m a t e r i a l s . We t h e r e f o r e examined samples from the same b a t c h o f c r y s t a l s f o r t r i b o l u m i n e s c e n c e a c t i v i t y and c r y s t a l s t r u c t u r e . The r e s u l t s a r e shown i n T a b l e I I , a l o n g w i t h some r e l a t e d compounds ( 6 , 12, 13) whose c r y s t a l s t r u c t u r e s were o b t a i n e d from the l i t e r a t u r e . Our r e s u l t s show a poor c o r r e l a t i o n o f t r i b o l u m i n e s c e n c e w i t h n o n c e n t r i c space group and r e v e a l a p o s s i b l e source o f dissymmetry i n the c r y s t a l t h a t c o u l d p e r m i t s i g n i f i c a n t charge s e p a r a t i o n d i s o r d e r . We found, f o r example, t h a t t r i b o l u m i n e s c e n t c r y s t a l s o f t r i e t h y l a m m o n i u m t e t r a k i s ( d i b e n z o y l m e t h a n a t o ) e u r o p a t e were d i s o r d e r e d ( p h e n y l r i n g s and alkylammonium c h a i n s ) ; c r y s t a l s c o n t a i n i n g d i c h l o r o m e t h a n e were p h o t o l u m i n e s c e n t b u t n o t t r i b o l u m i n e s c e n t and were n o t d i s o r d e r e d ( 1 8 ) . T r i b o l u m i n e s c e n c e and d i s o r d e r were a l s o o b s e r v e d i n the isomorphous l a n t h a n i d e s a l t s ( K i n g , W. ; R h e i n g o l d , A. L.; S w e e t i n g , L. M. u n p u b l i s h e d s t u d y ) . D i s o r d e r i s n o t common i n the 9 - s u b s t i t u t e d a n t h r a c e n e s , b u t i s o b s e r v e d f o r a n t h r y l e s t e r s 7 and 9. We c o n c l u d e t h a t d i s o r d e r may p r o v i d e l o c a l dissymmetry, d e f o r m i n g the l a t t i c e and a l l o w i n g charge a c c u m u l a t i o n . Unfor t u n a t e l y c r y s t a l l o g r a p h y cannot determine how the s i t e s o f d i f f e r e n t c o n f o r m a t i o n a r e d i s t r i b u t e d i n the c r y s t a l . We examined the l o c a l environment b y t e s t i n g some o f the m a t e r i a l s f o r t h e g e n e r a t i o n o f a second harmonic on l a s e r i r r a d i a t i o n ; no c o r r e l a t i o n w i t h t r i b o l u m i nescence was found. Some c r y s t a l s a r e o n l y t r i b o l u m i n e s c e n t when i m p u r i t i e s a r e p r e s e n t ; t h e i m p u r i t i e s may deform the l a t t i c e t o g e n e r a t e dissym metry and/or may p r o v i d e a p h o t o l u m i n e s c e n t s i t e . We have no r e a s o n t o b e l i e v e t h a t t h e c e n t r i c t r i b o l u m i n e s c e n t c r y s t a l s (e.g. 4) i n T a b l e I I a r e any l e s s pure t h a n the c e n t r i c n o n t r i b o l u m i n e s c e n t c r y s t a l s (e.g. 1 ) . T a b l e I I a l s o c o n t a i n s s e v e r a l examples o f n o n c e n t r i c c r y s t a l s w h i c h a r e n o t t r i b o l u m i n e s c e n t (e.g. 5, 1 3 ) . We a r e p a r t i c u l a r l y i n t r i g u e d b y the c o n t r a s t between 4 and 5: t h e r a c e m i c , c e n t r i c form i s t r i b o l u m i n e s c e n t b u t t h e e n a n t i o m e r i c a l l y homogeneous, n o n c e n t r i c form i s n o t . Spectroscopy The t r i b o l u m i n e s c e n c e spectrum can p r o v i d e i n f o r m a t i o n about s e v e r a l s t e p s i n the mechanism. F i g u r e 2a shows a t y p i c a l t r i b o l u m i -



13. SWEETING

Table I I . P r o p e r t i e s of P o t e n t i a l Materials Substituent

253


Space Group (1)

Tribolumin. Intensity (3)

Triboluminescent

Photolum. Emission Max.(nm)

SHG (2)

S e r i e s I : 9-• S u b s t i t u t e d A n t h r a c e n e s 1. C(CH ) 0H

C: P2 /c (4)

2. CH(CH )0H

N: I4,cd (4)

3. CH 0H

437,57

Spectroscopic Characterization of Minerals and Their Surfaces

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