The BaF X(X= Cl

Br

I):Eu

2+

is a kind of photo stimulated luminescence (PSL) material.The electron and hole traps play an important role in the mechanism of PSL.Both electron and hole leave respectively their traps by photo stimulation

then recombine with light emission at the luminescence center.In BaF X :Eu

2+

the vacancy of anion will attract an electron and form the F colour center which could be electron trap.Nevertheless

what will be the hole trap? It is not clear up to now.In this paper

the emission and absorption spectra of BaFBr and BaFBr:O

2-

samples have been investigated in order to ascertain the origin of hole traps in BaF X :Eu

2+

.In BaFBr:O

2-

sample

in which the concentration of O

2-

is about 8×10

-3

at%

the O

2-

ions occupy the site of fluorine ion.At room temperature

without pre irradiation

there are some emission peaks (at 330

345 and 540nm

respectively) and shoulders (near 440

480 and 502nm

respectively) in the emission spectra of BaFBr:O

2-

under the excitation of 240nm

as shown in Fig.1.But

no luminescence can be observed for BaFBr.However

for both BaFBr and BaFBr:O

2-

similar luminescence can be seen

after the pre irradiation with ultraviolet and vacuum ultraviolet(VUV) light of 50～400nm and/or 185nm

under the exitation of 240nm.Their emission peaks locate at 332

348

390

442

467

502 and 540nm approximately

although

the relative intensities of these peaks have minor differences for both samples(Fig.2).We believe that the origin of the luminescence of BaFBr and BaFBr:O

2-

is due to the oxygen impurity. Furthermore

taking the reflection spectrum of Au thin film as reference

the reflection spectra of BaFBr and BaFBr:O

2-

samples are measured in the range of 100～400nm at U10B station of the National Synchrotron Radiation Laboratory(NSRL).The absorption spectra are calculated from these reflection spectra by using K-K relation.It is found that there are four broad absorption sub bands in the absorption spectra of BaFBr

as well as in that of BaFBr:O

2-

(Fig.4).It means that the electron can be excited or ionized from the oxygen impurity into F center by UV and VUV light.These results support that the oxygen impurity could act as the hole trap in PSL materials.