PRESSURE-DEPENDENCE AND THERMAL QUENCHING OF CHROMIUM PHOTOLUMINESCENCE IN CS2NAYCL6CR3+

Photoluminescence spectra of the chromium-doped elpasolite Cs2NaYCl6:Cr3+ were measured at ambient and near liquid nitrogen temperatures as a function of pressure in a diamond anvil cell. A pressure-induced blue shift of the broad 4T2g --> 4A2g fluorescence band was observed, culminating in a crossing of the 4T2g and 2E(g) excited states as evidenced by the appearance of a structured E(g) --> 4A2g phosphorescence spectrum. Resolved vibronic structure of the latter permitted determination of vibration frequencies at high pressure. Evidence of a phase transition was observed near the highest pressures attained, almost-equal-to 11 GPa. The pressure dependence of the peak energy of the broad band was interpreted in terms of a pressure-dependent local compressibility. Measurements of photoluminescence lifetimes as functions of pressure and temperature established that the activation energy for thermal fluorescence quenching increases linearly at the rate of 1668 +/- 52 cm-1/GPa. A semi-empirical, two-accepting mode, linear- and quadratic-coupling model, calibrated at ambient pressure, predicts a rate of 1758 cm-1/GPa, in substantial agreement with experiment,