The luminescence centered at about 390nm due to 4f65d→4f7 transition of Eu2+ can be observed without X - ray or UV - light pre - irradiation for BaFBr: Eu2+、Ba0.95Sr0.05 FBr: Eu2 + and Ba0.95Ca0.05FBr: Eu2+ powder samples which can be excited by light with wave length longer than 400nm. It could be attributed to F centers which are formed in the preparation of samples. There are two broad bands in the photo - stimulated spectra. One peaked at 535nm results from the excitation of electrons at F(F- ) center

and the other at 708nm might be originated from the electron excitation of F(Br- ) center or F(Br- ) accumulators. If the Ba2+ (ion’s radius equals to 0. 135nm) in the samples were replaced by about 50% mol. of Sr2 + (ion’s radius equals to 0. 113nm) or Ca2 + (ion ’s radius equals to 0. 099nm)

the intensities of 535nm and 708nm bands decrease with the decrease of ion radius. On the other hand

the shoulders at 580nm and 650nm or 575nm and 645nm can appeare. In absorption spectra of 50 - 400nm range

one can observe the red - shift of 79nm

83nm peaks and new absorption peaks. It means that the new color centers: F(F -

Sr2 + ) .F(Br-

Sr2 + ) or F(F-

Ca2+ ) .F(Br-

Ca2+ ) are formed

when Ba2+ were replaced with Sr2+ or Ca2+ in samples. It corresponds to the shoulders in photo - stimulated spectra.