Pressure-Induced Transformation of Excitons in AgBr_1−xCl_x

Abstract

Pressure dependence of photoluminescence and absorption spectra in AgBr_1−xCl_x (x=1.0, 0.6 and 0.15) is investigated, using a diamond anvil cell with N₂ as pressure medium in order to generate good quality of hydrostatic pressure at 1.5 K. Pressure coefficients of self-trapped exciton states in AgCl, AgBr_0.4Cl_0.6 and that of free exciton state in AgBr_0.85Cl_0.15 are determined. After initial self-trapped exciton disappears at high pressures, new emission bands are found to appear in AgCl and AgBr_0.4Cl_0.6. These phenomena are ascribed to pressure-induced phase transition of excitons without accompanying a change of crystal structures.