Photoluminescence in Zn1-xCoxSe under hydrostatic pressure.

Abstract

We report on low temperature measurements of the pressure dependence of the photoluminescence (PL) associated with ${\mathrm{Co}}^{2+}$ in ZnSe performed in a diamond anvil cell. Two sharp emission peaks at \ensuremath{\sim}2.36 eV, labeled L and ${\mathit{L}}^{\ensuremath{'}}$, show a weak redshift under pressure with rapidly decreasing peak intensities. These results, together with the excitation energy and temperature dependence of the PL at 1 bar, allow for a critical examination of previous models proposed for these optical transitions. The PL data are discussed within the framework of conventional crystal-field theory based on the Racah and crystal-field parameters B, C, and \ensuremath{\Delta}(=10Dq). From this analysis, the normalized energy E/B is determined as a function of the normalized crystal field parameter Dq/B. Thus quantitative estimates for the enhancement in the p-d hybridization with pressure (evident in the line-shape profiles of the spectra) are deduced. The energy separation between L and ${\mathit{L}}^{\ensuremath{'}}$ decreases continuously for modest pressures (\ensuremath{\sim}1 GPa), and raises questions about the role of spin-orbit coupling in accounting for the splitting of this emission doublet. \textcopyright{} 1996 The American Physical Society.