Optical properties of scintillator material BaBr2 films

The BaBr2 films grown by vacuum thermal evaporation prefer three different completely (hkl) oriented growth at different growth parameters and each orientation develops strain due to residual stress. The optical absorption indicates a direct type band gap for these films. The band gap of each (hkl) orientation varies linearly with its uniaxial strain. The three (hkl) orientations show band gap anisotropy (2.94-4.25 eV). The negative (for (101) and (111)) and positive (for (013)) pressure coefficients of band gap are attributed to the strain in Br-Br and Ba-Br bonds along [hkl] respectively. The average pressure coefficient of band gap of all three orientations found to be significantly smaller than that calculated by volumetric pressure dependence.