Pressure dependence of the alexandrite emission spectrum

The dependence on hydrostatic pressure of the photoluminescent spectrum of alexandrite has been measured to 40 kbar, at 300 and 167 K. The R₁ and R₂ lines red shift linearly 0.27±{}0.01 and 0.33±{}0.01 {}/kbar, the same for both temperatures. Narrowing of the R lines with pressure is observed. The phonon sidebands are blue shifted with pressure. By analysis of these spectral shifts we calculate the anharmonicities of the ⁴A₂ and ²E states and explain the line narrowing. Thus from these analyses we propose that the linear dependency of the R-line transition energies on hydrostatic pressure results from anharmonic effects on the zero-point levels of the ⁴A₂ and ²E states, for Cr³⁺-doped materials in general.