Pressure evolution of LiBaF3:Eu2+ luminescence

We investigated the single crystals of LiBaF3 doped with Eu2+ using high pressure spectroscopy, where high pressure was applied in a diamond anvil cell. Photoluminescence, time-resolved luminescence and luminescence kinetics at pressures from ambient to 200 kbar and at temperatures from 10 K to ambient were studied. At ambient conditions the luminescence spectra consisted of sharp lines peaked at 360 nm attributed to the P-6(7/2) --> S-8(7/2) transitions in the 4f(7) electronic configuration of Eu2+ (the zero-phonon line and five single-phonon repetitions) and a broad band extending between 375 and 475 nm attributed to Eu2+ trapped exciton recombination. When pressure was increased the Eu2+ trapped exciton emission disappears and was replaced by the sharper band peaked at 355 nm, attributed to the 4f(6)5d(1)(eg). 4f(7)(S-8(7/2)) transition in Eu2+. To analyze the pressure dependence of luminescence spectra a model of impurity trapped excitons was developed. At temperatures lower than 50 K only the sharp lines related to P-6(7/2) --> S-8(7/2) transitions were observed for all pressures considered. Analysis of low temperature spectra allowed us to estimate the energies of the fifth phonon modes and the values of the Gruneisen parameters.