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Cross-relaxation for Tm3+ ions in indium-based glasses
] O U R N A L OF
NON~LLINE
Journal of Non-Crystalline Solids161 (1993) 294-296
~OLIDS
North-Holland
Cross-relaxation for Tm 3+ ions in indium-based glasses I.R. Mart~n and V.D. Rodrlguez Departamento Fisica Fundamental y Experimental, Unic'ersidad de La Laguna, 38204 La Laguna, Tenerife, Spain
R. Alcal~ and R. Cases ICMA, Universidad de Zaragoza - C.S.I.C., Plaza San Francisco s / n, 50009 Zaragoza, Spain
A spectroscopic study has been performed in indium-based fluoride glasses doped with different Tm 3+ concentrations (0.1, 0.5 and 2.5 mol%). The decay of the luminescence from the 3H 4, IG4, ID 2 and II6-3P0 levels has been measured for every concentration of Tm 3+. These decays are exponential for 0.1 mol% Tm 3+. When the concentration is enlarged, the decay curves become non-exponential because of cross-relaxation and energy diffusion. The decays are analyzed in the frame of the Yokota-Tanimoto energy transfer formula in the range of temperature 10-300 K.
1. Introduction H e a v y m e t a l f l u o r i d e glasses d o p e d with R E ions a r e g o o d c a n d i d a t e s for o p t i c a l devices as solid s t a t e lasers a n d a p p l i c a t i o n s in o p t i c a l fiber technology. In p a r t i c u l a r , T m 3 + ions a r e specially i n t e r e s t i n g b e c a u s e the e m i s s i o n f r o m the 3H 4 level to the g r o u n d state c o i n c i d e s with t h e wind o w o f t h e silica f i b e r n e a r 0.8 p~m. In this work, a s p e c t r o s c o p i c study of T m 3 + - d o p e d i n d i u m b a s e d f l u o r i d e glasses is p r e s e n t e d . S p e c i a l a t t e n tion has b e e n d e v o t e d to t h e excited s t a t e d y n a m ics o f t h e 3H 4 level trying to p r o v i d e new results with r e s p e c t to t h o s e r e p o r t e d in t h e l i t e r a t u r e for Similar glasses [1,2].
x ) I n F 3 , 20ZnF2, 20SrF2, 2 0 B a F 2 a n d x T m F 3 , with x e q u a l to 0.1 , 0.5 a n d 2.5. E m i s s i o n s p e c t r a w e r e o b t a i n e d by exciting the s a m p l e s with light from a 300 W X e arc l a m p p a s s e d t h r o u g h a 0.25 m d o u b l e m o n o c h r o m a t o r . F l u o r e s c e n c e was d e t e c t e d t h r o u g h a 0.25 m m o n o c h r o m a t o r with e i t h e r a p h o t o m u l t i p l i e r with m u l t i a l k a l i p h o t o c a t h o d e o r a r e f r i g e r a t e d PbS d e t e c t o r . S p e c t r a w e r e c o r r e c t e d by instrum e n t r e s p o n s e . L i f e t i m e s a n d emission decays w e r e m e a s u r e d using a flash l a m p with p u l s e s of 3 ~zs a n d a digital s t o r a g e oscilloscope. A cryog e n e r a t o r for the r a n g e o f t e m p e r a t u r e 10-300 K was used.
3. Results 2. Experimental T h e s a m p l e s u s e d in this w o r k w e r e p r e p a r e d with the following c o m p o s i t i o n s in m o l % : ( 4 0 -
Correspondence to: Dr I.R. Martin, Departamento Fisica Fun-
damental y Experimental, Universidad de La Laguna, 38204 La Laguna, Tenerife, Spain. Tel: +34-22 6037 78. Telefax: + 34-22 6300 40.
T h e e n e r g y level d i a g r a m of T m 3 + is shown in fig. 1. T h e f l u o r e s c e n t levels a r e i n d i c a t e d . F o r t h e s a m p l e s o f 0.1 m o l % o f T m 3+, the decays o f t h e emissions with p u l s e d excitation a r e fitted by single e x p o n e n t i a l . In table 1 t h e lifetimes obtained are presented. W h e n t h e d i f f e r e n t f l u o r e s c e n c e s p e c t r a corres p o n d i n g to 0.1 a n d 2.5 t o o l % T m 3+ a r e comp a r e d , it is f o u n d that in the m o s t c o n c e n t r a t e d
0022-3093/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved
I.R. Mart[net al. / Cross-relaxation for Tm 3 + ions in In-based glasses 40000
m
295
1.0
Sp ~pZ
T i n a÷
3plo,tI 6
3 6g 1 4" ~ "3 M, .
0 1 mol~
30000
"T
l
E o
•
ID2
•
IN4
aF,-baH6
:o., II
//
z . :k %
,,- -
40.6
20000
e,
mol~
25
0.8
DIFFUSION
:<
CROSS-RELAXATION 0.2
t";'
a l l ' - * aF4 '"
10000
__
3H~ 0.0 Z. . . . . . . . . . . . .
~oo
0
- -
~n6
900
~,
=,t ,, , ~ A ~ _ ~
., ,, . . . . . . . . .
11oo
t .....
~l,,,l!
laoo 15oo 17oo 19oo Wavelength (nm) Fig. 2. Emission spectra at room temperature of 0.1 and 2.5 moFA Tm 3+ in an indium-based glass.
SF 4
Fig. 1. Energy levels diagram of Tm 3+. The emitting levels are indicated. The mechanisms for cross-relaxation and diffusion for the 3H 4 level are shown.
teraction, Yokota and Tanimoto [3] obtained the following expression for the emission decay: sample cross-relaxation is involved in the decay. In the N I R emission spectra obtained exciting the 3H 4 level, shown in fig. 2, t h e 3 H 4 , 3H 6 --+3F4, 3F4 cross-relaxation channel permits an understanding of the observed differences. This channel of cross-relaxation is shown in fig. 1. Moreover, the decay curves from the different emitting levels are non-exponential for the sample with the highest concentration of Tm 3+. The decay curves for t h e 3H 4 level at different temperatures are shown in fig. 3.
t I(t)
(x e x p
4 w 3/2
r
3
(1 + 10.87x + ×
)1/2 NA( t C D A
15.50X2)3/4)
1 + 8.743x
,
(1)
where r is the lifetime, N A is the concentration of
acceptors
materials),
(non-excited
CDA
is
the
ions
in
single
donor-acceptor
doped energy
transfer parameter (cross relaxation in single
4. Discussion Migration of energy can be described as a diffusion process. Considering dipole-dipole ind Table 1 Experimental lifetimes for 0.1 mol% Tm 3+ and energy transfer parameters for cross-relaxation and diffusion ( x l 0 -39 cm6s -t) obtained with the 2.5 mol% Tm 3+ sample at room temperature
1I 6 3P0 1D. l G; 3H 4
Texp
CDA
Coo
85 IXS 63 pxs 0.73 ms 1.9 ms
1.35 4.4 7.65 1.3
1.2 0.19 0.0 0.30
e"
..................
0.4
..... 12 ......... 0.8
............ iii ........... / 1.2
1.6
t(ms) Fig. 3. Decay curves corresponding to the 3H 4 ~ 3 H 6 emission in a 2.5 tool% TmF 3 sample at different temperatures.
296
I.R. Mart[net al. / Cross-relaxation for Tm 3 + ions in In-based glasses
T h e decay of the fluorescent emission of the 3H 4 level shows a strong t e m p e r a t u r e dependence as can be seen in fig. 3 where the decay curves are given at four different temperatures. T h e c o r r e s p o n d i n g energy transfer parameters for diffusion (COD) and cross-relaxation (CDA) have b e e n plotted in fig. 4. It can be seen that, except at very low temperatures, cross-relaxation is m u c h larger than energy diffusion. This is in a g r e e m e n t with results obtained by many authors in systems d o p e d with T m 3 + [2].
1.6
D O 1.2
2 O
O
O 30.4
O
O
~0.0
.........
O
O
i ......... 50
O
~ ......... 100
O
i ......... 150
i ......... 200
i ......... 250
i .... 300
T (K) Fig. 4. Energy transfer parameters for cross relaxation (n) and diffusion (©) for the 3H 4 level of Tm3+ in an indiumbased glass as a function of the temperature.
d o p e d materials) and x is given by x = oc~l/3t
2/3,
(2)
where D is the diffusion constant which is related with the d o n o r - d o n o r energy transfer p a r a m e t e r by the expression of Trlifaj [4]: 1
D = 7(4-rr/3)
4/3
4/3 N D CDD,
(3)
where N D is the c o n c e n t r a t i o n of d o n o r ions. T h e decay curves from the LI6-3P0, 1D2, 1G 4 and 3H 4 levels have b e e n fitted to the Y o k o t a T a n i m o t o formula. T h e energy transfer p a r a m e ters COA and C o D at r o o m t e m p e r a t u r e for every level are given in table 1.
5. C o n c l u s i o n s
T h e excited state dynamics of the different emitting levels of the T m 3+ have been studied. By fitting the decay curves of the luminescence to the Y o k o t a - T a n i m o t o expression, the energy transfer p a r a m e t e r s for cross-relaxation and diffusion have b e e n o b t a i n e d for all the emitting levels. F o r t h e 3H 4 level, these p a r a m e t e r s are t e m p e r a t u r e - d e p e n d e n t and the cross-relaxation is the d o m i n a n t process.
References
[1] C. Guery, J.L. Adam and J. Lucas, J. Lumin. 42 (1988) 181. [2] A. Brenier, C. Pedrini, B. Moine, J.L. Adam and C. Pledel, Phys. Rev. B41 (1990) 5364. [3] M. Yokota and O. Tanimoto, J. Phys. Soc. Jpn. 22 (1967) 779. [4] M. Trlifaj, Czech. J. Phys. 8 (1958) 510.
NON~LLINE
Journal of Non-Crystalline Solids161 (1993) 294-296
~OLIDS
North-Holland
Cross-relaxation for Tm 3+ ions in indium-based glasses I.R. Mart~n and V.D. Rodrlguez Departamento Fisica Fundamental y Experimental, Unic'ersidad de La Laguna, 38204 La Laguna, Tenerife, Spain
R. Alcal~ and R. Cases ICMA, Universidad de Zaragoza - C.S.I.C., Plaza San Francisco s / n, 50009 Zaragoza, Spain
A spectroscopic study has been performed in indium-based fluoride glasses doped with different Tm 3+ concentrations (0.1, 0.5 and 2.5 mol%). The decay of the luminescence from the 3H 4, IG4, ID 2 and II6-3P0 levels has been measured for every concentration of Tm 3+. These decays are exponential for 0.1 mol% Tm 3+. When the concentration is enlarged, the decay curves become non-exponential because of cross-relaxation and energy diffusion. The decays are analyzed in the frame of the Yokota-Tanimoto energy transfer formula in the range of temperature 10-300 K.
1. Introduction H e a v y m e t a l f l u o r i d e glasses d o p e d with R E ions a r e g o o d c a n d i d a t e s for o p t i c a l devices as solid s t a t e lasers a n d a p p l i c a t i o n s in o p t i c a l fiber technology. In p a r t i c u l a r , T m 3 + ions a r e specially i n t e r e s t i n g b e c a u s e the e m i s s i o n f r o m the 3H 4 level to the g r o u n d state c o i n c i d e s with t h e wind o w o f t h e silica f i b e r n e a r 0.8 p~m. In this work, a s p e c t r o s c o p i c study of T m 3 + - d o p e d i n d i u m b a s e d f l u o r i d e glasses is p r e s e n t e d . S p e c i a l a t t e n tion has b e e n d e v o t e d to t h e excited s t a t e d y n a m ics o f t h e 3H 4 level trying to p r o v i d e new results with r e s p e c t to t h o s e r e p o r t e d in t h e l i t e r a t u r e for Similar glasses [1,2].
x ) I n F 3 , 20ZnF2, 20SrF2, 2 0 B a F 2 a n d x T m F 3 , with x e q u a l to 0.1 , 0.5 a n d 2.5. E m i s s i o n s p e c t r a w e r e o b t a i n e d by exciting the s a m p l e s with light from a 300 W X e arc l a m p p a s s e d t h r o u g h a 0.25 m d o u b l e m o n o c h r o m a t o r . F l u o r e s c e n c e was d e t e c t e d t h r o u g h a 0.25 m m o n o c h r o m a t o r with e i t h e r a p h o t o m u l t i p l i e r with m u l t i a l k a l i p h o t o c a t h o d e o r a r e f r i g e r a t e d PbS d e t e c t o r . S p e c t r a w e r e c o r r e c t e d by instrum e n t r e s p o n s e . L i f e t i m e s a n d emission decays w e r e m e a s u r e d using a flash l a m p with p u l s e s of 3 ~zs a n d a digital s t o r a g e oscilloscope. A cryog e n e r a t o r for the r a n g e o f t e m p e r a t u r e 10-300 K was used.
3. Results 2. Experimental T h e s a m p l e s u s e d in this w o r k w e r e p r e p a r e d with the following c o m p o s i t i o n s in m o l % : ( 4 0 -
Correspondence to: Dr I.R. Martin, Departamento Fisica Fun-
damental y Experimental, Universidad de La Laguna, 38204 La Laguna, Tenerife, Spain. Tel: +34-22 6037 78. Telefax: + 34-22 6300 40.
T h e e n e r g y level d i a g r a m of T m 3 + is shown in fig. 1. T h e f l u o r e s c e n t levels a r e i n d i c a t e d . F o r t h e s a m p l e s o f 0.1 m o l % o f T m 3+, the decays o f t h e emissions with p u l s e d excitation a r e fitted by single e x p o n e n t i a l . In table 1 t h e lifetimes obtained are presented. W h e n t h e d i f f e r e n t f l u o r e s c e n c e s p e c t r a corres p o n d i n g to 0.1 a n d 2.5 t o o l % T m 3+ a r e comp a r e d , it is f o u n d that in the m o s t c o n c e n t r a t e d
0022-3093/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved
I.R. Mart[net al. / Cross-relaxation for Tm 3 + ions in In-based glasses 40000
m
295
1.0
Sp ~pZ
T i n a÷
3plo,tI 6
3 6g 1 4" ~ "3 M, .
0 1 mol~
30000
"T
l
E o
•
ID2
•
IN4
aF,-baH6
:o., II
//
z . :k %
,,- -
40.6
20000
e,
mol~
25
0.8
DIFFUSION
:<
CROSS-RELAXATION 0.2
t";'
a l l ' - * aF4 '"
10000
__
3H~ 0.0 Z. . . . . . . . . . . . .
~oo
0
- -
~n6
900
~,
=,t ,, , ~ A ~ _ ~
., ,, . . . . . . . . .
11oo
t .....
~l,,,l!
laoo 15oo 17oo 19oo Wavelength (nm) Fig. 2. Emission spectra at room temperature of 0.1 and 2.5 moFA Tm 3+ in an indium-based glass.
SF 4
Fig. 1. Energy levels diagram of Tm 3+. The emitting levels are indicated. The mechanisms for cross-relaxation and diffusion for the 3H 4 level are shown.
teraction, Yokota and Tanimoto [3] obtained the following expression for the emission decay: sample cross-relaxation is involved in the decay. In the N I R emission spectra obtained exciting the 3H 4 level, shown in fig. 2, t h e 3 H 4 , 3H 6 --+3F4, 3F4 cross-relaxation channel permits an understanding of the observed differences. This channel of cross-relaxation is shown in fig. 1. Moreover, the decay curves from the different emitting levels are non-exponential for the sample with the highest concentration of Tm 3+. The decay curves for t h e 3H 4 level at different temperatures are shown in fig. 3.
t I(t)
(x e x p
4 w 3/2
r
3
(1 + 10.87x + ×
)1/2 NA( t C D A
15.50X2)3/4)
1 + 8.743x
,
(1)
where r is the lifetime, N A is the concentration of
acceptors
materials),
(non-excited
CDA
is
the
ions
in
single
donor-acceptor
doped energy
transfer parameter (cross relaxation in single
4. Discussion Migration of energy can be described as a diffusion process. Considering dipole-dipole ind Table 1 Experimental lifetimes for 0.1 mol% Tm 3+ and energy transfer parameters for cross-relaxation and diffusion ( x l 0 -39 cm6s -t) obtained with the 2.5 mol% Tm 3+ sample at room temperature
1I 6 3P0 1D. l G; 3H 4
Texp
CDA
Coo
85 IXS 63 pxs 0.73 ms 1.9 ms
1.35 4.4 7.65 1.3
1.2 0.19 0.0 0.30
e"
..................
0.4
..... 12 ......... 0.8
............ iii ........... / 1.2
1.6
t(ms) Fig. 3. Decay curves corresponding to the 3H 4 ~ 3 H 6 emission in a 2.5 tool% TmF 3 sample at different temperatures.
296
I.R. Mart[net al. / Cross-relaxation for Tm 3 + ions in In-based glasses
T h e decay of the fluorescent emission of the 3H 4 level shows a strong t e m p e r a t u r e dependence as can be seen in fig. 3 where the decay curves are given at four different temperatures. T h e c o r r e s p o n d i n g energy transfer parameters for diffusion (COD) and cross-relaxation (CDA) have b e e n plotted in fig. 4. It can be seen that, except at very low temperatures, cross-relaxation is m u c h larger than energy diffusion. This is in a g r e e m e n t with results obtained by many authors in systems d o p e d with T m 3 + [2].
1.6
D O 1.2
2 O
O
O 30.4
O
O
~0.0
.........
O
O
i ......... 50
O
~ ......... 100
O
i ......... 150
i ......... 200
i ......... 250
i .... 300
T (K) Fig. 4. Energy transfer parameters for cross relaxation (n) and diffusion (©) for the 3H 4 level of Tm3+ in an indiumbased glass as a function of the temperature.
d o p e d materials) and x is given by x = oc~l/3t
2/3,
(2)
where D is the diffusion constant which is related with the d o n o r - d o n o r energy transfer p a r a m e t e r by the expression of Trlifaj [4]: 1
D = 7(4-rr/3)
4/3
4/3 N D CDD,
(3)
where N D is the c o n c e n t r a t i o n of d o n o r ions. T h e decay curves from the LI6-3P0, 1D2, 1G 4 and 3H 4 levels have b e e n fitted to the Y o k o t a T a n i m o t o formula. T h e energy transfer p a r a m e ters COA and C o D at r o o m t e m p e r a t u r e for every level are given in table 1.
5. C o n c l u s i o n s
T h e excited state dynamics of the different emitting levels of the T m 3+ have been studied. By fitting the decay curves of the luminescence to the Y o k o t a - T a n i m o t o expression, the energy transfer p a r a m e t e r s for cross-relaxation and diffusion have b e e n o b t a i n e d for all the emitting levels. F o r t h e 3H 4 level, these p a r a m e t e r s are t e m p e r a t u r e - d e p e n d e n t and the cross-relaxation is the d o m i n a n t process.
References
[1] C. Guery, J.L. Adam and J. Lucas, J. Lumin. 42 (1988) 181. [2] A. Brenier, C. Pedrini, B. Moine, J.L. Adam and C. Pledel, Phys. Rev. B41 (1990) 5364. [3] M. Yokota and O. Tanimoto, J. Phys. Soc. Jpn. 22 (1967) 779. [4] M. Trlifaj, Czech. J. Phys. 8 (1958) 510.