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XES PATTERN OF BaLaGa3O7:Nd SINGLE CRYSTALS
G. Jasiolek, M. Berkowski, W. Piekarczyk
To cite this version:
G. Jasiolek, M. Berkowski, W. Piekarczyk. XES PATTERN OF BaLaGa3O7:Nd SIN- GLE CRYSTALS. Journal de Physique Colloques, 1987, 48 (C9), pp.C9-1063-C9-1066.
�10.1051/jphyscol:19879193�. �jpa-00227310�
JOURNAL DE PHYSIQUE
Colloque C9, suppl6ment au n012, Tome 48, d6cembre ,1987
XES PATTERN OF BaLaGa,O,:Nd SINGLE CRYSTALS
G. JASIQZEK, M. BERKOWSKI and W. PIEKARCZYK
I n s t i t u t e o f P h y s i c s , P o l i s h Academy o f Sciences, A l . ~ o t n i k o w 32/46, PL-02 668 Warsaw, Poland
Rdsum4
Analyse des s p e c t r e s d'emission X de Ba, La ( L & ~ , L & ~ , ~ ) e t Nd (L&,
,
Lp2, 5) e t dans l e s r e g i o n s d e s s e u i l s a #absorption L du La e t L2 du Ba dans BaLaGa307 m o n o c r i s t a u avec Nd (jusqu'au 3 2.1 % a t . ) e s t presentCe. Les r e s u l t a t s s o n t considerds par des d6placements chimiques e t p a r d e s p o s i t i o n s e t i n t e n s i t d s d e s s a t e l l i t e s . It e s t confirme? que l ' i n t e r a c t b n d e La avec de l a r k s e a u c r i s t a l l i n des c r i s t a u x e s t f a i b l e e t que l e niveau 4f du La p a r t i c i p e dans l ' i n t e n s i t 6 d e l a 5d-
2s t r a n s i t i o n . Le niveau 4f du Nd e s t p l u s l o i n de l a bande de valence dans l e cas de 2.1 %at.A b s t r a c t
I n v e s t i g a t i o n h a s been made on t h e L&4 X-ray emission l i n e of barium and lanthanum, on t h e Llj l i n e of lanthanum, La1 and
L 2 , 3
P2,15
l i n e s of neodymium, a s w e l l a s on t h e L emission band o f lanthanum and L2 band o f barium i n t h e BaLaCa 3 0 s i n g l e3 7
c r y s t a l s doped with Nd up t o 2.1 at.%
.
The measurements have b e e n performed using a s i n g l e c r y s t a l spectrometer of t h e Johann type i n t h e e l e c t r o n probe microanalysis mode. The che- m i c a l s h i f t s and t h e s a t e l l i t e s i n t e n s i t i e s observed f o r t h e doped c r y s t a l s i n comparison with t h e r e f e r e n c e samples: BaF2LaF3 and a m e t a l l i c neodymium allowed us t o d e s c r i b e t h e r o l e o f t h e 4f e l e c t r o n s of neodymium and of t h e 4f s h e l l of l a n -
thanum i n t h e valence band of t h e c r y s t a l s . I, I n t r o d u c t i o n
Doping of t h e BaLaGa307 c r y s t a l s w i t h Nd l e a d s t o t h e formation of a new i n t e r e s t i n g l a s e r - m a t e r i a l . On t h e o t h e r hand, it i n v o l v e s some problems i n t h e growth processes, d i f f e r e n t from t h e s e ones connected with t h e p r e p a r a t i o n of t h e h o s t m a t e r i a l [I]
.
Becauseof t h e s m a l l e r i o n i c r a d i u s of neodymium than of lanthanum [2]
,
ani n t e r a c t i o n between c a t i o n s changes. It can be expected t h a t the dop- i n g with Nd, from 0 - 3 at.% t o 2.1 at.%, used by us f o r t h e l a s e r ex- periments, g i v e s a m o d i f i c a t i o n of t h e valence band of t h e m a t e r i a l i n v e s t i g a t e d
[a.
To know an i n f l u e n c e of t h e doping considered on t h e e l e c t r o n i c s t r u c t u r e of BaLaGa30., * . c r y s t a l s , t h e X-ray emission s p e c t r e scopy XES h a s been chosen.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19879193
J O U R N A L DE PHYSIQUE
11. Experimental
Neasurements have been made on the L214 X-ray emiseion l i n e of barium and lanthanum, near a b s o r p t i o n edge Lj band of l a n t h a - num and near a b s o r p t i o n edge L, band o f barium, a s w e l l a s on t h e
L
LP2.., and L&, l i n e s of neoci-ymium and l i n e o f lanthanum.
~ l l ' e k ~ e r i m e n t s have been performed u s i n g a s p e c t r o m e t e r o f t h e J o h a m t y p e w i t h a LiF a n a l y s i n g c r y s t a l ( i n t e r p l a n a r s p a c i n g d -; 2.11135
8 )
i n t h e EPIVIA-JXA-5OA
b] .
A n a c c e l e r a t i n g v o l t a g e of 2 5 kV and e l e c t r o n beam c u r r e n t o f 0.3 pA heve been used. The -Q9 Line of chromium h a s been a p p l i e d a s t h e r e f e r e n c e l i n e f o r t h e j n v e s t j g a t i a n s of t h e n e a r a b s o r p t i o n edge bands. mS s t u d i e s followed t h e a n a l v s i s o f t h e r e a l c o n c e n t r a t i o n s of t h e c a t i o n s forming t h e c r y s t a l s and a t e s t of t h e i s homogeneity, The X-ray emission i n o u r experiments came from t h e 7 )unt h i c k l a y e r s of samples.
A l l measurements were c a r r i e d o u t or, t h e (001) o r i e n t e d surfr?rces,whis,l?
were p e r p e n d i c u l a r t o t h e growth d i r e c t i o n . The samples were t a k e n from t h e c e n t r a l p a r t s of t h e s i n g l e c r y s t a l s grown by t h e C z c c h r a l s k i method, Each spectrum w a s r e g i s t e r e d s t e p by s t e p . F.nergetlc wid.th o f a g i v e n s t e p was d i f f e r e n t f o r v a r i u s s p e c t r a and it came from the ran- ge of 0.34-0.44 eV. The ~ i n g l e c r ~ s t a l s of BaP? and Lap3 a s well a s a m e t a l l i c neodymium were used a s t h e r e f e r e n c e s t a n d a r i a .
111. R e s u l t s
The q u a n t i t a t i v e a n a l y s i s of t h e chemical cornposi.tion of t h e samples showed that; t h e bzrium concentra-tion i s equal t o 20.72 0.2 a t . % i n t h e a l l samples and tine c o n c e n t r a t i o n of t h e r a r e e a r t h s i s equal t o 18.8 f 0.2 at.%
,
w i t h 0.3, 0.5, 1 .1 and 2.1 at.% o f neodymium.The d i s t r i b u t i o n s of t h e c a t i o n elements were homogeneous.
I t was confirmed t h a t t h e energy o f t h e e l e c t r o n t r a n s i . t i o n from 5d s h e l l o f lanthanum, which c o n t r i b u t e s i n t h e chemical bond of l a n t h a - num with oxygen, t o t h e 2~~~~ s u b s h e l l f o r EaLaCa O with t h e h i g h e s t
3 7
c o n c e n t r a t i o n of neodvmium d e c r e a s e s by 2.4 eV, i n comparison with t h e s i t u a t i o n f o r t h e Lap3 c r y s t a l (pig..,)
.
The chemical s h i f t , a l s o to- wa.rds t h e lower e n e r g i e s , connected w i t h t h e 5 s s h e l l was e s t i m a t e d on 1 eV. 1.t can be s e e n t h a t t h e d e v i a t i o n s observed s l i g h t l y i n c r e a s e w i t h t h e neodymium c o n c e n t r a t i o n .The. r e s u l t s o b t a i n e d f o r barium showed t h a t t h e 5s s h e l l (the R maxi- m u m i n Fig.2) s h i f t s by "18 eV towards t h e h i g h e r e n e r g i e s f o r t h e BaLaGa307:Nd c r y s t a l , i n comparison w i t h its p o s i t i o n f o r BaF7.
Fig.1. La L, emission
J
band of BaLaGa3Q7:2.?at.Y/o of Nd (I)
,
:?.? at.% o f Nd (2) and LaF (3).
5493 5473 5453 5433
ENERGY Lev1
Fig.2. Ba L2 emission band o f BaLaGa307:2.1 at.% of ne- odymium (1) and BaF2 (2)
.
The A maximum i s connected with t h e overlap of barium and ox gen va-
l e n c e o r b i t a l s . Furthermore, t h e C maximum i s caused by t h e ~ , L ~ N & - ~ Coster-Kronig t r a n s i t i o n . They s h i f t e d a l s o towards t h e higher aneGgy s i d e . I n t h e c r y s t a l s i n v e s t i g a t e d t h e energy of t h e e l e c t r o n t r a n s i - t i o n between 6s s h e l l and t h e 2p,l7 subshell i s disguised ( ~ i g . 2 ) by t h e 4s
-
2pqI7 t r a n s i t i o n of lan<hanum electrons. Therefore, it i s n o t possible' t o d e t e c t t h e e n e r g e t i c s h i f t of t h e considered t r a n s i - t i o n , However, it can be expected t h a t a shift towards t h e higher energy .of about 2 eV takes place i n t h i s case.The main maximum of each spectrum i n t h e f i g u r e 3 and i n t h e next one has been located a t t h e zero p o s i t i o n on t h e energy scale. The s p e c t r a have been normalized t o t h e main maximum. The shape of t h e Lk4 l i n e obtained f o r barium ( ~ i ~ . 3 ) revealed, a f t e r the deconvolution proce- dure, t h e s a t e l l i t e maximum a t +8 eV and t h e D maximum a t +14.3 eV.
This l a s t maximum i s v i s i b l e only f o r t h e heavyly doped c r y s t a l . This maximum i s connected with t h e i n t e r a c t i o n between barium and oxygen electrons. I t corresponds t o t h e B maximum i n Fig.2
.
RELATIVE ENERGY lev1 Fig.3. The BaLa4 emission
RELATIVE ENERGY I ~ V I
Fig.4. The LaLh4 emission s p e c t r a f o r : BaLaGa307:
2.1 at.% N d (1) and BaLaCap7: 0.5 at.% Nd (2)
s p e c t r a for: BaLaGa 0 2.1 at.% Nd (1) and 3 7:
BaLaGa307: 1.1 at.% ~ d f 2 )
JOURNAL DE PHYSIQUE
The half-width of t h e l i n e considered i n c r e a s e d by 0.9 eV, i n compari- son with undoped c r y s t a l [3]
.
The shape of t h e L& l i n e of La ( ~ i ~ . 4 ) showed t h e s a t e l l i t e maximum, E, a t + I 2 eV f o r t h e sample doped with 1 .I at.% and a t +I 5 eV f o r t h e sample w i t h 2.1 a t . % .This maximum i s connected with t h e 5d-
2s t r a n s i t i o n , The r e l a t i v e i n t e n s i t y of t h i s maximum d e c r e a s e s markedly coming t o t h e heavyly doped sample. The half-width of t h i s l i n e d i d n o t change markedly,
i n comparison with t h e s i t u a t i o n f o r t h e pure c r y s t a l .A s a t e l l i t e appeared a t t h e low energy s i d e of t h e La, spectrum of Nd.
I t i s connected with t h e m u l t i p l e t s p l i t t i n g of t h e 4d s u b s h e l l [5]*
Such s a t e l l i t e i s r e g i s t e r e d a l s o f o r a m e t a l l i c sample, However, 312 it d i d n o t appear f o r t h e sample w i t h 1 .I at.% of Nd. The p o s i t i o n of t h i s s a t e l l i t e i s equal t o + I 8 eV f o r t h e doped c r y s t a l and t o + I 6 eV f o r t h e r e f e r e n c e sample, The half-width of t h i s l i n e f o r t h e c r y s t a l s i s wider by 2 eV t h a n f o r a m e t a l l i c Nd.
The Lf$2,15 l i n e of Nd was r e g i s t e r e d c l o s e t o t h e L& l i n e of La.
I t was confirmed t h a t t h e half-width of t h e LP2,? l i n e f o r t h e crys- 293 t a l s i s 1 eV narrower t h a n i n t h e c a s e of m e t a l l i c Nd.
The o b s e r v a t i o n of t h e s a t e l l i t e maximum a t t h e low energy s i d e of t h e Lx2,3 l i n e of La, connected with t h e e n e r g e t i c a l l y forbidden L L M
'1 3 4 Coster-Kronig t r a n s i t i o n and a n e l e c t r o n t r a n s f e r of t h e 3d e l e c t r o n s t o t h e o u t e r s h e l l s and with t h e L1L3N4,5 t r a n s i t i o n , allows us t o t h e conclusion t h a t t h e r e l a t i v e i n t e n s i t y of t h i s s a t e l l i t e i s t h e same a s f o r a lowly doped c r y s t a l [3] , I t is by 8-70 % h i g h e r t h a n f o r t h e pure c r y s t a l .
I V . Discussion
Because of t h e 3dq0
-
3dl0-%fn t r a n s i t i o n and t h e 4f- 5d e l e c t r o n i c t r a n s f e r t h e d e c r e a s e of t h e E maximum w i t h t h e conceri- t r a t i o n of Nd can be t r e a t e d a s a d e c r e a s e of t h e e f f i c e n c y of t h e bond of La. I f t h e E maximum c o n s i d e r a s a r e s u l t of t h e t r a n s i t i o n between 2p s h e l l of oxygen and t h e 2s s h e l l of La only, t h e above con- c l u s i o n w i l l be s t i l l v a l i d.
The o v e r l a p between lanthanum and oxygen valence o r b i t a l s becomes s l i g h t e r with t h e neodymium concentration.The o p p o s i t e conclusion t a k e s place f o r t h e barium i n t e r a c t i o n i n t h e BaLaGa 0 l a t t i c e . These behaviours a r e confirmed by an i n c r e a s e of
3 7
t h e binding energy of t h e 2p312 e l e c t r o n s of La. I n comparison w i t h t h e s i t u a t i o n f o r LaF t h e 4f s h e l l of La i n t h e BaLaGa307:Nd c r y s t a l s
can be considered through t h e 5d 3
-
4f t r a n s i t i o n a s 4fn,
with l>n>O.
The 4f e l e c t r o n s of Nd a r e s t r o n g l y bonded i n t h e c r y s t a l s only i n t h e c a s e of t h e Nd c o n c e n t r a t i o n below 1 .I at.%. For t h e h i g h e s t i n v e s t i g a - t e d c o n c e n t r a t i o n of Nd t h e 4f e l e c t r o n s a r e l o c a l i z e d c l o s e r t o t h e i n n e r s h e l l s t h a n t o t h e valence band.
The high d e v i a t i o n of t h e La c o n c e n t r a t i o n i n t h e c r y s t a l s from t h e s t o i c h i o m e t r i c one i s caused by t h e s l i g h t bond of La i n t h e l a t t i c e .
References
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71
(1985) 395
.
2. Shannon, R.D. and P r e w i t t , C.T., Acta C r y s t a l l .
B25
(1969) 925 3. Jasiolek,G. ,Berkowski,M. and Piekarczyk,W., Chemtronics1
(I 986) 121 4< Reed,S,J,B, i n : E l e c t r o n Microbeam Analysis,Cambridge U n i v e r s i t yP r e s s , Cambridge, U.K. 1975
,
p.765.Salem, S.I. and S c o t t , B.L. Phys.Rev.
