Effect of hydrostatic and chemical pressure on BaF2 and BaF2: Eu2+ crystals

Abstract

The effect of hydrostatic pressure on a BaF2 crystal was studied within the shell model in the pair-wise potential approximation. The structural phase transition from the cubic to orthorhombic phase was simulated. The behavior of the unit-cell parameters of the α-and β-BaF2 phases under hydrostatic pressure (from 0 to 12 GPa) was investigated. The fundamental vibration frequencies of BaF2 under hydrostatic pressure (0–3.5 GPa) were calculated for both phases. The effect of chemical pressure on the BaF2 crystal was studied by simulating Ba1−xMexF2 mixed crystals (Me=Ca, Sr). It was shown that at impurity concentrations up to 15–20 at. % the lattice constant varies in the same way as it does when hydrostatic pressure increases to Pc, which corresponds to a phase transition to the orthorhombic phase. The effect of chemical and hydrostatic pressure on BaF2: Eu2+ doped crystals was also studied. The dependence of the absorption and luminescence zero-phonon line shift on the Eu2+-ligand distance was calculated.