Optical spectroscopy and four-wave mixing in emerald

The optical-spectroscopic properties of Cr³⁺ ions in Be₃{Al}₂$(${SiO}₃)₆ crystals were investigated using several techniques. The temperature dependencies of the fluorescence intensity and lifetime were measured between 10 and 300 K and shown to be due to thermal population effects in the ⁴T₂ and ²E levels. The results of time-resolved site-selection spectroscopy measurements show that the Cr³⁺ ions occupy several different types of sites having nonequivalent crystal fields, and that spectral energy transfer takes place between ions in different types of sites. The results of four-wave mixing measurements show the presence of long-range resonant energy migration among the chromium ions and provide information about the radiationless relaxation rate from the ⁴T₂ level to the ²E level.