Abstract

Be₃Al₂(SiO₃)₆:Cr³⁺ (emerald) has important potential applications as a tunable vibronic laser material. The spectra of emerald exhibit structure which can be attributed to Cr³⁺ ions occupying three nonequivalent crystal field sites. We present here the results of characterizing the optical properties of the Cr³⁺ ions in emerald using time-resolved site-selection (TRSS) spectroscopy and four-wave mixing (FWM) spectroscopy techniques. The temperature and crossing angle dependence of the FWM signal decay rate are consistent with scattering of the probe beam from a laser-induced population grating of Cr³⁺ ions. The time evolution of the FWM signal at low temperatures is consistent with the theory of partially coherent exciton migration. The diffusion coefficient D for spatial migration of energy was determined from theoretical fits to the FWM data. D was found to increase exponentially with temperature, consistent with phonon-assisted energy transfer processes. TRSS results demonstrate the presence of short-range energy transfer between ions in nonequivalent types of site, which is significantly different from the long-range migration process probed by FWM measurements.

© 1987 Optical Society of America