LUMINESCENCE OF MnF2 SAMPLES CONTAINING OXYGEN

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LUMINESCENCE OF MnF2 SAMPLES

CONTAINING OXYGEN

F. Rodriguez, M. Moreno, J. Baruchel, J. Henry

To cite this version:

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JOURNAL

DE

PHYSIQUE

Colloque

C7,

suppl6ment au nOIO, T o m e

46,

octobre 1985 page C7-155

LUMINESCENCE OF MnF2 SAMPLES CONTAINING OXYGEN

++

F. Rodriguez, M. Moreno, J. ~aruchel+ and J.Y. Henry

Dpto de Optica y E.M., FacuZtad de Ciencias, 39005 Santander, Spain ' ~ n s t i t u t Laue-Langevin, 156X, 38042 GrenobZe Cedex, France

++

_{LEZ'I-IRDI, CENG,} _85X,_{38041 GrenobZe Cedex, France}

Abstract

-

A deep trap, having a depth A=1200f 100 cm-I ,has been identi- fied in five MnF2 samples containing different concentrations of oxygen. In these samples above 40K the emission band is always peaked at 605 nm and the quenching temperature can be up to 150K.

5

-

INTRODUCTION

Above 4K the luminescence of MnF2 is essentially determined by the kind and concentration of impurities present in the sample. The results by Goldberg et a1 /1/ indi- &ate that below 25K the emission band i2+peaked at-580 nm, this emission b ing

8+

ass ciated to shaliom traps formed by Mn ions perturbed by unintentional Mg

,

2+

Zn

'*,

and Ca ions in close positions /1,2/. Above -25K it has been found that the emitted intensity decreases progressively when temperature is raised and it is com- pletely quenched at-105K /I/. At the same time in this range of temperature the ma-

Ximum of the emission band goes progressively from -580 run to -660 nm. This fact indicates the existence of several deeper traps, which up to now, have not been iden- tified /2/. In this work we report the identificatjon of a deep trap in MnF2

I1

-

EXPERIMENTAL

we have investigated five samples (A,B,C,D and E) of MnF extracted from a Bridgman 2

grown single where analysis indicates the presence of oxygen (an impurity very di- fficult to avoid in MnF2 / 3 , 4 / ) : a few small green points which where characterized @s being MnO, were observed on the surface of the upper region of the rod. Samples

A , B and C correspond to the initial state of growth while sample E has the highest oxygen concentration. Lumirescence in the range 10

-

150 K has been measured uslng a Jobin-Ivon JY-3D spectrofluorimeter and an Air-Products closed circuit cryostat.

I11

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RESULTS

On figure 1 is depicted the emission spectrum for sample E for 10 < T < 115 K. While the features o6served below -25K are similar to those reported by Goldberg et a1 /1/ in the 40 - 120 K range, the emission band is always peaked at 605 nm. The variation of the emission spectrum with temperature for the other samples is similar to that given in figure 1 as regards the peak position but not, their intensity.

On figure 2 is plotted Ct~e vuriution ol' Lire c~~~iLtecl ir~Lenvity a L 605 n l n (tukir~g us unity the corresponding at 10K) for the five samples. It can be seen that this relative intensity increases for samples D and E which are the closest to the end of crystallization.

On figure 3 it is plotted the decay of luminescence in the 90

-

120 K region for

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JOURNAL DE PHYSIQUE

-1 for sample D. The value of the trap depth,A, derived from it, i s A = 1200+ 100 cm

.

The same value is also obtained for the other samples.

Concerning zero-phonon emission lines, we have detecfed in our samples at 10K, only ons+placed at 552.5 nm involving a value

A

= 324 cm which could be associated to Ca traps.

IV

-

DISCUSSION

At variance with previous results on other MnF2 samples, the emission spectrum of our five samples above-40K is governed by trap. The increase of the relative intensity at 605 nm for samples D and E can be explained assuming a) that the ki-

ller concentration is quite similar for all samples, b ) that the trap associated to the 605 nm emission involves oxygen.

It is noteworthy that the subtitution of 'F by 02- as ligagd of ~ n * + tends to increase lODq and then to decrease the energy of the6,$ ( S ) + T ( G ) transition giving rise the formation of a trap. Concerning

,

this valje can aiso be estimated from spectroscopic dfta. Taking S E w 2. 850 cm-' we find that the zero-phonon line should

be at 17348 cm- for the 3rap. Vlhen this figure is compareP to 18424 cm- corres- ponding to unperturbed Mn + ions, we estimate

A

2.1050 cm in agreement with the value derived from the luminescence decay.

6 6 0 6 0 0 6 5 0 7 0 0

W A V E L E N G T H ( n m )

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T E M P E R A T U R E ( K )

Fig. 2

-

Relative intensity of emission at 605 nm as a function of temperature for sample A ( + ) , B ( A ) ,

C

( * ) ,

D

( a ) and

E

( e ) .

Sample

E

is the furthest from the sharp end while A is the nearest.

Fig. 3

-

Plot of the Ln (I /I

-

1) vs the inverse of temperature.

I

.

is the highest observedointensity of the 605 nm emission band.

REFERENCES

/1/ Goldberg, V. et a1 in Luminpscence of Inorganic Solids, Ed by B. Di Bartolo, Plenum (New York 19781, p 603.

/2/ Wilson, B., Yen, W., Hegarty, J. and Imbusch, G., Phys. Rev. (1979) 4238. /3/ Park, D.S. and Nowick, A.S., J. Phys. Chem. Solids, 37 (1976) 607.