Temperature dependence of the chromium(III) R1 linewidth in emerald

► Temperature dependence of the R1 linewidth in emerald is reported. ► The temperature dependent contribution to the linewidth varies from 0.6 MHz at 6.5 K to ∼420 GHz at 240 K. ► A line shift of ∼570 GHz towards the red is observed from 6 to 240 K. ► Two-phonon Raman scattering and the direct one-phonon process dominate above and below 60 K, respectively. ► Low-energy phonon leads to deviation of standard behavior at lowest temperatures.