- Email: [email protected]
Differently charged forms of electron centers in KI
Volume 32A, n u m b e r 6
DIFFERENTLY
PHYSICS
CHARGED
FORMS
L. N O S E N Z O ,
LETTERS
OF
24 August 1970
ELECTRON
IN
CENTERS
KI
E. R E G U Z Z O N I a n d G. S A M O G G I A
Istituto di F i s i c a Generale A . Volta, Pavia, Italy Gruppo Nazionale di Struttura della Materia del C . N . R .
V. UDOD T. G . S h e v s c h e n k o State University, K i e v , USSR
Received 8 JuLy 1970
In this p a p e r we give evidence of the existence of new absorption bands a s s o c i a t e d with M+, R +, M' and R' c e n t e r s in KI c r y s t a l s .
It i s w e l l k n o w n t h a t M , R a n d N c e n t e r s a r e e l e c t r i c a l l y n e u t r a l c l u s t e r s of a n i o n v a c a n c i e s a n d t r a p p e d e l e c t r o n s . It i s u s e f u l , a s s h o w n b y B r o t h e r s [1], to t a k e i n t o a c c o u n t d i f f e r e n t l y c h a r g e d f o r m s of F a g g r e g a t e s in o r d e r to s t u d y t h e m o d e l of t h e s e c e n t e r s a n d t h e i r f o r m a t i o n mechanism. All these centers have been extens i v e l y s t u d i e d in KC1, K B r a n d NaC1 b u t d a t a r e g a r d i n g KI a r e l a c k i n g . We report here the modulation spectrum ind u c e d a t L N T b y a n e x t e r n a l e l e c t r i c f i e l d in KI crystals containing by time F, F + M and F + M +
R centers. The technique used has been prev i o u s l y a p p l i e d in t h e c a s e of K C I a n d K B r c r y s t a l s [2]. T h e c u r v e s h a v e b e e n a n a l y s e d b y c o m paring them with the results concerning KCI and K B r r e p o r t e d in r e f . [2]. O u r m e a s u r e m e n t s h a v e b e e n p e r f o r m e d w i t h a n e l e c t r i c f i e l d of 40 k V p / c m a t 35 c p s . T h e w a v e l e n g t h s of t h e o b s e r v e d p e a k s a r e s h o w n in t a b l e 1. T y p i c a l r e s u l t s of o p t i c a l d e n s i t y m e a s u r e m e n t s a t L N T a r e : OD F = 2, OD M = 0.5; OD R = 0.5; OD N -- 0.5. T h e d a s h e d c u r v e in fig. 1 s h o w s t h a t , in
Table 1 Peak position at LNT of optical absorption bands in KC1, KBr and KI given in gin.
Kcl
KBr
K,
"LI
M
0.803
0.888
1.02
1.37
1.44
1.93
M'
1.94
2.15
2.4
R1
0.66
0.73
0.827
4-
R2
0.73
0.81
0.905
6-
R3
0.508
0.63
$-
R4
0.465 0.94
1.01
0.55
R~ R~
0.76 0.54
0.89
R,~ , R1
0.49
1.12
M
l
1
f.-
M+
R~
F
'42 0.8
1
12
1.4
101214
t
-
t
0.6
1.5
1.6
1.76
R2
1.6
1.72
1.91
N1
0.97
1.14
1.23
N1
1.93
2.2
2.29
!
1.6
18
2
2.2
2.4
2.6
),(y.m)--
Fig. 1, Change in the optical absorption of a KI c r y s t a l containing F and M c e n t e r s . 415
Volume 32A, number 6
PHYSICS
c r y s t a l s c o n t a i n i n g only F c e n t e r s , by i n c r e a s ing the e l e c t r i c field, a d e c r e a s e of a b s o r p t i o n in the F band r e g i o n ( A I / I ) F > 0 together with an i n c r e a s e in the F ' r e g i o n ( A I / I ) F , < 0 is o b served. When the c r y s t a l c o n t a i n s M c e n t e r s also, one o b s e r v e s both a d e c r e a s e in the modulation s p e c t r u m in the M r e g i o n Qtmax = 1.02 gm) and two new p o s i t i v e b a n d s in the i n f r a r e d region (fig. 1, d i r e c t curve). T h e s e bands a r e a t t r i b uted to F~. (;tmax = 1.93 gm) and to M' (~max = 2.4 gm) f f e n t e r s r e s p e c t i v e l y . When the c r y s t a l c o n t a i n s R c e n t e r s , m o d u lation in the a b s o r p t i o n of M and d e r i v e d b a n d s is n e g l i g i b l e in c o m p a r i s o n with that of R bands (fig. 2, d i r e c t curve). In this c a s e , the c o m -s
R, R~
R, g, R~ F
u
~
N.
-z
"°r / WIll '
R; !
N~'
-04
/ /
.o.2 1 e~
\ 18
~(,m)-
t
2
t '\
\ 2.6
2.4
),(pro) Fig. 2. Change in the optical absorption spectrum of a KI crystal containing F, M, R and N centers.
416
24 August 1970
plexity of the modulation s p e c t r u m r e q u i r e s a m o r e detailed a n a l y s i s . F i r s t we s h a h d i s c u s s n e g a t i v e bands a s s o c i a t e d with n e u t r a l R c e n t e r t r a n s i t i o n s . B e s i d e s the R 1 (;tmax = 0.827 ~m) and R 2 (kma x = 0.905 ~m) b a n d s , a negative a b s o r p t i o n change about 0.56 ~tm is o b s e r v e d , together with a shift of the F band. This shift is shown in detail in the i n s e r t of fig. 2, w h e r e the dashed and d i r e c t c u r v e s show the modulation effect when a c r y s t a l c o n t a i n s only F c e n t e r s and F + R c e n t e r s r e s p e c t i v e l y . The dotted line shows the d i f f e r e n c e between the two c u r v e s . T h e s e changes a r e to be a s c r i b e d to R 3 I;tmax = 0.63 bLm) and R 4 (kmax = 0.55 /~m) bands. In the 0.5-1.2 ~ m r a n g e a set of p o s i t i v e bands a s s o c i a t e d with R c e n t e r s a r e s u p e r i m posed on the F ' band. The f i r s t positive band which we call R~ (~tmax = 1.12 ~m) c o r r e s p o n d s to the optical abkorption band a s s o c i a t e d with F~ c e n t e r s by Kouvalis and H e r s h [3]. The other b a n d s can be a t t r i b u t e d to e l e c t r o n i c t r a n s i t i o n s of ionized R c e n t e r s to higher excited s t a t e s . We note that the a b s o r p t i o n change at 0.95 ~ m is too l a r g e to be a t t r i b u t e d to F ' modulation only. As in KC1 and KBr, p r o b a b l y the R~ t r a n s i t i o n is s u p e r i m p o s e d on the R 2 band. In the n e a r i n f r a f r e d region the R~ (~tmax = 1.76 ~tm) and R 2 (~max = 1.91 ~m) bands a r e seen. When N 1 c e n t e r s a r e also p r e s e n t , b e s i d e s an i n c r e a s e of t r a n s m i s s i o n in the N 1 r e g i o n , a p o s i t i v e band about 2.3 ~ m has been o b s e r v e d , p r o b a b l y a s s o c i a t e d with N~ c e n t e r s (dashed c u r v e in fig. 2).
\
/ 2.2
ET T E RS
Reference s [1] A.D.Brothers and D.W.Lynch, Phys. Rev. 174 (1968) 958. [2] L. Nosenzo, E. Reguzzoni and G. Samoggia, Phys. Status Solidi 38. (1970) 369. [3] A.Kouvalis and H. Hersh, Phys. Rev. 188 0969) 1439.
DIFFERENTLY
PHYSICS
CHARGED
FORMS
L. N O S E N Z O ,
LETTERS
OF
24 August 1970
ELECTRON
IN
CENTERS
KI
E. R E G U Z Z O N I a n d G. S A M O G G I A
Istituto di F i s i c a Generale A . Volta, Pavia, Italy Gruppo Nazionale di Struttura della Materia del C . N . R .
V. UDOD T. G . S h e v s c h e n k o State University, K i e v , USSR
Received 8 JuLy 1970
In this p a p e r we give evidence of the existence of new absorption bands a s s o c i a t e d with M+, R +, M' and R' c e n t e r s in KI c r y s t a l s .
It i s w e l l k n o w n t h a t M , R a n d N c e n t e r s a r e e l e c t r i c a l l y n e u t r a l c l u s t e r s of a n i o n v a c a n c i e s a n d t r a p p e d e l e c t r o n s . It i s u s e f u l , a s s h o w n b y B r o t h e r s [1], to t a k e i n t o a c c o u n t d i f f e r e n t l y c h a r g e d f o r m s of F a g g r e g a t e s in o r d e r to s t u d y t h e m o d e l of t h e s e c e n t e r s a n d t h e i r f o r m a t i o n mechanism. All these centers have been extens i v e l y s t u d i e d in KC1, K B r a n d NaC1 b u t d a t a r e g a r d i n g KI a r e l a c k i n g . We report here the modulation spectrum ind u c e d a t L N T b y a n e x t e r n a l e l e c t r i c f i e l d in KI crystals containing by time F, F + M and F + M +
R centers. The technique used has been prev i o u s l y a p p l i e d in t h e c a s e of K C I a n d K B r c r y s t a l s [2]. T h e c u r v e s h a v e b e e n a n a l y s e d b y c o m paring them with the results concerning KCI and K B r r e p o r t e d in r e f . [2]. O u r m e a s u r e m e n t s h a v e b e e n p e r f o r m e d w i t h a n e l e c t r i c f i e l d of 40 k V p / c m a t 35 c p s . T h e w a v e l e n g t h s of t h e o b s e r v e d p e a k s a r e s h o w n in t a b l e 1. T y p i c a l r e s u l t s of o p t i c a l d e n s i t y m e a s u r e m e n t s a t L N T a r e : OD F = 2, OD M = 0.5; OD R = 0.5; OD N -- 0.5. T h e d a s h e d c u r v e in fig. 1 s h o w s t h a t , in
Table 1 Peak position at LNT of optical absorption bands in KC1, KBr and KI given in gin.
Kcl
KBr
K,
"LI
M
0.803
0.888
1.02
1.37
1.44
1.93
M'
1.94
2.15
2.4
R1
0.66
0.73
0.827
4-
R2
0.73
0.81
0.905
6-
R3
0.508
0.63
$-
R4
0.465 0.94
1.01
0.55
R~ R~
0.76 0.54
0.89
R,~ , R1
0.49
1.12
M
l
1
f.-
M+
R~
F
'42 0.8
1
12
1.4
101214
t
-
t
0.6
1.5
1.6
1.76
R2
1.6
1.72
1.91
N1
0.97
1.14
1.23
N1
1.93
2.2
2.29
!
1.6
18
2
2.2
2.4
2.6
),(y.m)--
Fig. 1, Change in the optical absorption of a KI c r y s t a l containing F and M c e n t e r s . 415
Volume 32A, number 6
PHYSICS
c r y s t a l s c o n t a i n i n g only F c e n t e r s , by i n c r e a s ing the e l e c t r i c field, a d e c r e a s e of a b s o r p t i o n in the F band r e g i o n ( A I / I ) F > 0 together with an i n c r e a s e in the F ' r e g i o n ( A I / I ) F , < 0 is o b served. When the c r y s t a l c o n t a i n s M c e n t e r s also, one o b s e r v e s both a d e c r e a s e in the modulation s p e c t r u m in the M r e g i o n Qtmax = 1.02 gm) and two new p o s i t i v e b a n d s in the i n f r a r e d region (fig. 1, d i r e c t curve). T h e s e bands a r e a t t r i b uted to F~. (;tmax = 1.93 gm) and to M' (~max = 2.4 gm) f f e n t e r s r e s p e c t i v e l y . When the c r y s t a l c o n t a i n s R c e n t e r s , m o d u lation in the a b s o r p t i o n of M and d e r i v e d b a n d s is n e g l i g i b l e in c o m p a r i s o n with that of R bands (fig. 2, d i r e c t curve). In this c a s e , the c o m -s
R, R~
R, g, R~ F
u
~
N.
-z
"°r / WIll '
R; !
N~'
-04
/ /
.o.2 1 e~
\ 18
~(,m)-
t
2
t '\
\ 2.6
2.4
),(pro) Fig. 2. Change in the optical absorption spectrum of a KI crystal containing F, M, R and N centers.
416
24 August 1970
plexity of the modulation s p e c t r u m r e q u i r e s a m o r e detailed a n a l y s i s . F i r s t we s h a h d i s c u s s n e g a t i v e bands a s s o c i a t e d with n e u t r a l R c e n t e r t r a n s i t i o n s . B e s i d e s the R 1 (;tmax = 0.827 ~m) and R 2 (kma x = 0.905 ~m) b a n d s , a negative a b s o r p t i o n change about 0.56 ~tm is o b s e r v e d , together with a shift of the F band. This shift is shown in detail in the i n s e r t of fig. 2, w h e r e the dashed and d i r e c t c u r v e s show the modulation effect when a c r y s t a l c o n t a i n s only F c e n t e r s and F + R c e n t e r s r e s p e c t i v e l y . The dotted line shows the d i f f e r e n c e between the two c u r v e s . T h e s e changes a r e to be a s c r i b e d to R 3 I;tmax = 0.63 bLm) and R 4 (kmax = 0.55 /~m) bands. In the 0.5-1.2 ~ m r a n g e a set of p o s i t i v e bands a s s o c i a t e d with R c e n t e r s a r e s u p e r i m posed on the F ' band. The f i r s t positive band which we call R~ (~tmax = 1.12 ~m) c o r r e s p o n d s to the optical abkorption band a s s o c i a t e d with F~ c e n t e r s by Kouvalis and H e r s h [3]. The other b a n d s can be a t t r i b u t e d to e l e c t r o n i c t r a n s i t i o n s of ionized R c e n t e r s to higher excited s t a t e s . We note that the a b s o r p t i o n change at 0.95 ~ m is too l a r g e to be a t t r i b u t e d to F ' modulation only. As in KC1 and KBr, p r o b a b l y the R~ t r a n s i t i o n is s u p e r i m p o s e d on the R 2 band. In the n e a r i n f r a f r e d region the R~ (~tmax = 1.76 ~tm) and R 2 (~max = 1.91 ~m) bands a r e seen. When N 1 c e n t e r s a r e also p r e s e n t , b e s i d e s an i n c r e a s e of t r a n s m i s s i o n in the N 1 r e g i o n , a p o s i t i v e band about 2.3 ~ m has been o b s e r v e d , p r o b a b l y a s s o c i a t e d with N~ c e n t e r s (dashed c u r v e in fig. 2).
\
/ 2.2
ET T E RS
Reference s [1] A.D.Brothers and D.W.Lynch, Phys. Rev. 174 (1968) 958. [2] L. Nosenzo, E. Reguzzoni and G. Samoggia, Phys. Status Solidi 38. (1970) 369. [3] A.Kouvalis and H. Hersh, Phys. Rev. 188 0969) 1439.