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Raman spectrum of VK centers in KCl:Ag crystals
Volume 31A, number 8
PHYSICS LETTERS
s u r r o u n d i n g this s a m p l e as a function of t e m p e r a ture. T h e r e i s a d i s t i n c t l y m a r k e d m a x i m u m of the s u s c e p t i b i l i t y and, s e p a r a t e d by about 2 deg r e e s , a s u p e r c o n d u c t i n g t r a n s i t i o n . The v a l u e s of Tc, 0c and ×max lie on the c o r r e s p o n d i n g c u r v e s in fig. 1. T h i s r e s u l t was r e p r o d u c e d by another s a m p l e of the s a m e composition. In this case the s u p e r c o n d u c t i n g t r a n s i t i o n was also chequed by the d i s a p p e a r a n c e of the e l e c t r i c a l r e s i s t i v i t y . T h e r e f o r e , f r o m these m e a s u r e m e n t s , c o e x i s t e n c e s e e m s to be p o s s i b l e , but is not proven. One cannot exclude an inhomogeneous Tb d i s t r i b u t i o n on a s u b m i c r o s c o p i c scale. The m e a s u r e d change in the s u s c e p t i b i l i t y i n d i c a t e s a c o m plete shielding in the s u p e r c o n d u c t i n g state in c o n t r a s t to the alloys of CeRu 2 with Gd. The diff e r e n t b e h a v i o u r of the alloys containing Gd and Tb r e s p e c t i v e l y is not understood. One r e a s o n ***
RAMAN
SPECTI~UM
OF
20 April 1970
may be another type of m a g n e t i c o r d e r i n g (e.g. s p i r a l or f e r r o m a g n e t i c ) which may be not as des t r u c t i v e for s u p e r c o n d u c t i v i t y as a f e r r o m a g netic one. A s i m i l a r c u r v e as in fig. 2 was publ i s h e d by W i l l e n s and Buehler [5] for MoC with 2- at% Fe.
Refer~ces 1. B.T. Matthias, H. Suhl and E. Corenzwit, Phys. Rev. Letters 1 (1958) 449. 2. R.M. Bozorth, D. D. Davis and A. J. Williams, Phys. Rev. 119 (1961) 1570. 3. M. Wilhelm and B. Hitlenbrand, J. Phys. Chem. Solids 31 (1970) 559. 4. M. Wilhelm and B. Hiltenbrand, Stanford Conf. on Superconductivity, August 1969. 5. R. H. Willens and E. Buehler, J. Appl. Phys. 38 (1967) 405. *
V K CENTERS
IN K C I : A g
CRYSTALS
*
A. N. J E T T E , J. BOHANDY, J. C. MURPHY
Applied Physics Laboratory, Johns Hopkins University, Silver spring, Maryland 20910, USA and D. C. O'SHEA ** and C. M. WILSON
Physics Department, Johns Hopkins University, Baltimore, Maryland 21218, USA Received 10 March 1970
Raman spectra from an X-irradiated KCI:Ag crystal at 77°K is reported. A signal at 235 cm -1 is assigned to the VK center on the basis of experimental and theoretical considerations.
We wish to r e p o r t the R a m a n s p e c t r a [1] of c r y s t a l s of KC1 doped with 0.5% m o l a r AgC1. The c r y s t a l s were X - i r r a d i a t e d at 77°K f r o m a tungsten t a r g e t (50 kV, 40 mA) for t i m e s r a n g i n g f r o m o n e - h a l f to s e v e r a l hours. S p e c t r a were t a k e n u s i n g the 5145 /~ line of an argon ion l a s e r (~500 mW) and counting t e c h n i q u e s to r e c o r d the data. Fig. 1 shows typical s p e c t r a taken at 77°K before and after X - i r r a d i a t i o n . After X - i r r a d i a tion, a s m a l l Stokes peak at 5208/~, 235 cm -1 f r o m the Rayleigh line, i s s u p e r i m p o s e d on the b r o a d l a s e r - i n d u c e d r e d f l u o r e s c e n c e . T h i s peak b l e a c h e d r a p i d l y with continued l a s e r radiation. It was e x p e r i m e n t a l l y c o n f i r m e d by us utilizing optical a b s o r p t i o n m e a s u r e m e n t s , that the two p r e d o m i n a n t color c e n t e r s p r o d u c e d in KChAg c r y s t a l s X - i r r a d i a t e d at 77°K a r e s i l v e r a t o m s
at s u b s t i t u t i o n a l s i t e s [2] and VK c e n t e r s [3]. Decay of these color c e n t e r populations at 77°K occ u r s via r e c o m b i n a t i o n of photochemically r e l e a s ed Ag ° e l e c t r o n s with VK c e n t e r s or v i a an Ag ° VK c e n t e r t u n n e l i n g p r o c e s s which p r o d u c e s a yellow p h o s p h o r e s c e n c e . Both the 235 cm -1 Stokes peak and the yellow p h o s p h o r e s c e n c e were locally b l e a c h e d by the 5145 ~ l a s e r line in a g r e e m e n t with t h e i r a s s i g n m e n t to a c o m m o n o r i g i n [4]. The close a g r e e m e n t of the 235 cm -1 to the 265 cm -1 peak o b s e r v e d by Hass and G r i s c o m [5] for C12 in * Work supported in part by the Naval Ordnance Systems Command, U.S. Department of the Navy, under Contract NOw 62-0604-c. ** Present address: Gordon McKay Laboratory, Harvarc~ University, Cambridge, Massachusetts 02138. 449
Volume 31A, number 8
PHYSICS LETTERS
20April1970
nantly due to the dipolar coupling of the excited 2 + 2 TM ~.g state to the ~'u ground state. The f i r s t o r d e r c r o s s section for R a m a n s c a t t e r i n g i s : T - 77eK BEFORE X - Irradiation
Q(o~)
4 4 e oJ -
-
/ °~2-+ u + / ~u"2; g
/
-
12.2c 1
2P/R 2 1 - e-fl Stokes x ~ ::~6--~-ox e-~ anti-Stokes 1 - e -fl where fl =- ~iwo/kT, Ro i s the i n t e r n u c l e a r distance of the m o l e c u l e - i o n , and Mo i s the r e d u c e d m a s s of the o s c i l l a t o r . Here, o~ i s the l a s e r f r e quency ¢o2~+, 2 ~ i s the uv t r a n s i t i o n frequency,
T • 77"K
AFTER X - IrradiatiOn at 7 7 ° K
and S is the s c a l a r magnitude of the Poynting vector. Substituting the p a r a m e t e r s for the V~- c e n t e r [7], and a s s u m i n g 1017 c e n t e r s per cm 3, ~ie expected n u m b e r of photons per second p e r unit solid angle in this e x p e r i m e n t would be 107 and 105 for the Stokes and a n t i - S t o k e s shifts r e s p e c t i v e l y . T h i s a c c o u n t s for the a b s e n c e of the anti-Stokes line in our data.
Fig. 1. Raman spectra at N2 temperature of KCI:Ag.
References
p o t a s s i u m - c h l o r i d e - b o r a t e g l a s s e s in which no s i l v e r i s p r e s e n t t e n d s to c o n f i r m the p r e s e n t assignment. T h e o r e t i c a l l y , the magnitude of the v i b r a t i o n a l f r e q u e n c y given by the R a m a n e x p e r i m e n t s a g r e e s f a v o r a b l y with the 260 c m - 1 for free C12 as d e t e r m i n e d by the SCF-MO c a l c u l a t i o n s of Wahl and G i l b e r t [6]. The expected r e l a t i v e i n t e n s i t i e s of the Stokes and a n t i - S t o k e s l i n e s can be e s t i m a t e d by c o n s i d e r i n g an o r i e n t e d gas of CI~. m o l e c u l e s and a s s u m i n g that the p o l a r i z a b i l i t y i s p r e d o m i * * * * *
450
1. This work was briefly reported at the March 1969 meeting of the American Physical Society: J. Bohandy, J. C. Murphy, A. N. Jette, D. C. O'Shea and C. M. Wilson, Ball. Am. Phys. Soc. 14 (1969) 343. 2. C.J. Delbeeq, W.Hayes, M.C.M.O'Brien and P.H. Yuster, Proc. Roy. Soc. (London) 271 (1963) 243. 3. T.G. Castner and W. K ~ z i g , J. Phys. Chem. Solids 3 (1957) z78. 4. c . J . Delbecq, A. K. Ghosh and P. H. Yuster, Hull. Am. Phys. Soc. 9 (1964) 629. 5. M. H a s s and D. L. G r i s c o m , J. Chem. Phys. 51 (1969) 5185. 6. A.C. Wahl and T. L. Gilbert, unpublished. 7. A.N. Jette, T. L. Gilbert and T. P. Das, Phys. Rev. 184 (1969) 884.
PHYSICS LETTERS
s u r r o u n d i n g this s a m p l e as a function of t e m p e r a ture. T h e r e i s a d i s t i n c t l y m a r k e d m a x i m u m of the s u s c e p t i b i l i t y and, s e p a r a t e d by about 2 deg r e e s , a s u p e r c o n d u c t i n g t r a n s i t i o n . The v a l u e s of Tc, 0c and ×max lie on the c o r r e s p o n d i n g c u r v e s in fig. 1. T h i s r e s u l t was r e p r o d u c e d by another s a m p l e of the s a m e composition. In this case the s u p e r c o n d u c t i n g t r a n s i t i o n was also chequed by the d i s a p p e a r a n c e of the e l e c t r i c a l r e s i s t i v i t y . T h e r e f o r e , f r o m these m e a s u r e m e n t s , c o e x i s t e n c e s e e m s to be p o s s i b l e , but is not proven. One cannot exclude an inhomogeneous Tb d i s t r i b u t i o n on a s u b m i c r o s c o p i c scale. The m e a s u r e d change in the s u s c e p t i b i l i t y i n d i c a t e s a c o m plete shielding in the s u p e r c o n d u c t i n g state in c o n t r a s t to the alloys of CeRu 2 with Gd. The diff e r e n t b e h a v i o u r of the alloys containing Gd and Tb r e s p e c t i v e l y is not understood. One r e a s o n ***
RAMAN
SPECTI~UM
OF
20 April 1970
may be another type of m a g n e t i c o r d e r i n g (e.g. s p i r a l or f e r r o m a g n e t i c ) which may be not as des t r u c t i v e for s u p e r c o n d u c t i v i t y as a f e r r o m a g netic one. A s i m i l a r c u r v e as in fig. 2 was publ i s h e d by W i l l e n s and Buehler [5] for MoC with 2- at% Fe.
Refer~ces 1. B.T. Matthias, H. Suhl and E. Corenzwit, Phys. Rev. Letters 1 (1958) 449. 2. R.M. Bozorth, D. D. Davis and A. J. Williams, Phys. Rev. 119 (1961) 1570. 3. M. Wilhelm and B. Hitlenbrand, J. Phys. Chem. Solids 31 (1970) 559. 4. M. Wilhelm and B. Hiltenbrand, Stanford Conf. on Superconductivity, August 1969. 5. R. H. Willens and E. Buehler, J. Appl. Phys. 38 (1967) 405. *
V K CENTERS
IN K C I : A g
CRYSTALS
*
A. N. J E T T E , J. BOHANDY, J. C. MURPHY
Applied Physics Laboratory, Johns Hopkins University, Silver spring, Maryland 20910, USA and D. C. O'SHEA ** and C. M. WILSON
Physics Department, Johns Hopkins University, Baltimore, Maryland 21218, USA Received 10 March 1970
Raman spectra from an X-irradiated KCI:Ag crystal at 77°K is reported. A signal at 235 cm -1 is assigned to the VK center on the basis of experimental and theoretical considerations.
We wish to r e p o r t the R a m a n s p e c t r a [1] of c r y s t a l s of KC1 doped with 0.5% m o l a r AgC1. The c r y s t a l s were X - i r r a d i a t e d at 77°K f r o m a tungsten t a r g e t (50 kV, 40 mA) for t i m e s r a n g i n g f r o m o n e - h a l f to s e v e r a l hours. S p e c t r a were t a k e n u s i n g the 5145 /~ line of an argon ion l a s e r (~500 mW) and counting t e c h n i q u e s to r e c o r d the data. Fig. 1 shows typical s p e c t r a taken at 77°K before and after X - i r r a d i a t i o n . After X - i r r a d i a tion, a s m a l l Stokes peak at 5208/~, 235 cm -1 f r o m the Rayleigh line, i s s u p e r i m p o s e d on the b r o a d l a s e r - i n d u c e d r e d f l u o r e s c e n c e . T h i s peak b l e a c h e d r a p i d l y with continued l a s e r radiation. It was e x p e r i m e n t a l l y c o n f i r m e d by us utilizing optical a b s o r p t i o n m e a s u r e m e n t s , that the two p r e d o m i n a n t color c e n t e r s p r o d u c e d in KChAg c r y s t a l s X - i r r a d i a t e d at 77°K a r e s i l v e r a t o m s
at s u b s t i t u t i o n a l s i t e s [2] and VK c e n t e r s [3]. Decay of these color c e n t e r populations at 77°K occ u r s via r e c o m b i n a t i o n of photochemically r e l e a s ed Ag ° e l e c t r o n s with VK c e n t e r s or v i a an Ag ° VK c e n t e r t u n n e l i n g p r o c e s s which p r o d u c e s a yellow p h o s p h o r e s c e n c e . Both the 235 cm -1 Stokes peak and the yellow p h o s p h o r e s c e n c e were locally b l e a c h e d by the 5145 ~ l a s e r line in a g r e e m e n t with t h e i r a s s i g n m e n t to a c o m m o n o r i g i n [4]. The close a g r e e m e n t of the 235 cm -1 to the 265 cm -1 peak o b s e r v e d by Hass and G r i s c o m [5] for C12 in * Work supported in part by the Naval Ordnance Systems Command, U.S. Department of the Navy, under Contract NOw 62-0604-c. ** Present address: Gordon McKay Laboratory, Harvarc~ University, Cambridge, Massachusetts 02138. 449
Volume 31A, number 8
PHYSICS LETTERS
20April1970
nantly due to the dipolar coupling of the excited 2 + 2 TM ~.g state to the ~'u ground state. The f i r s t o r d e r c r o s s section for R a m a n s c a t t e r i n g i s : T - 77eK BEFORE X - Irradiation
Q(o~)
4 4 e oJ -
-
/ °~2-+ u + / ~u"2; g
/
-
12.2c 1
2P/R 2 1 - e-fl Stokes x ~ ::~6--~-ox e-~ anti-Stokes 1 - e -fl where fl =- ~iwo/kT, Ro i s the i n t e r n u c l e a r distance of the m o l e c u l e - i o n , and Mo i s the r e d u c e d m a s s of the o s c i l l a t o r . Here, o~ i s the l a s e r f r e quency ¢o2~+, 2 ~ i s the uv t r a n s i t i o n frequency,
T • 77"K
AFTER X - IrradiatiOn at 7 7 ° K
and S is the s c a l a r magnitude of the Poynting vector. Substituting the p a r a m e t e r s for the V~- c e n t e r [7], and a s s u m i n g 1017 c e n t e r s per cm 3, ~ie expected n u m b e r of photons per second p e r unit solid angle in this e x p e r i m e n t would be 107 and 105 for the Stokes and a n t i - S t o k e s shifts r e s p e c t i v e l y . T h i s a c c o u n t s for the a b s e n c e of the anti-Stokes line in our data.
Fig. 1. Raman spectra at N2 temperature of KCI:Ag.
References
p o t a s s i u m - c h l o r i d e - b o r a t e g l a s s e s in which no s i l v e r i s p r e s e n t t e n d s to c o n f i r m the p r e s e n t assignment. T h e o r e t i c a l l y , the magnitude of the v i b r a t i o n a l f r e q u e n c y given by the R a m a n e x p e r i m e n t s a g r e e s f a v o r a b l y with the 260 c m - 1 for free C12 as d e t e r m i n e d by the SCF-MO c a l c u l a t i o n s of Wahl and G i l b e r t [6]. The expected r e l a t i v e i n t e n s i t i e s of the Stokes and a n t i - S t o k e s l i n e s can be e s t i m a t e d by c o n s i d e r i n g an o r i e n t e d gas of CI~. m o l e c u l e s and a s s u m i n g that the p o l a r i z a b i l i t y i s p r e d o m i * * * * *
450
1. This work was briefly reported at the March 1969 meeting of the American Physical Society: J. Bohandy, J. C. Murphy, A. N. Jette, D. C. O'Shea and C. M. Wilson, Ball. Am. Phys. Soc. 14 (1969) 343. 2. C.J. Delbeeq, W.Hayes, M.C.M.O'Brien and P.H. Yuster, Proc. Roy. Soc. (London) 271 (1963) 243. 3. T.G. Castner and W. K ~ z i g , J. Phys. Chem. Solids 3 (1957) z78. 4. c . J . Delbecq, A. K. Ghosh and P. H. Yuster, Hull. Am. Phys. Soc. 9 (1964) 629. 5. M. H a s s and D. L. G r i s c o m , J. Chem. Phys. 51 (1969) 5185. 6. A.C. Wahl and T. L. Gilbert, unpublished. 7. A.N. Jette, T. L. Gilbert and T. P. Das, Phys. Rev. 184 (1969) 884.