Influence of fluorescence reabsorption and trapping on solid-state optical cooling

We analyze the random process of fluorescence reabsorption and trapping in solid-state optical materials in general and its influence on the efficiency of optical cooling of solids by anti-Stokes fluorescence in particular. Using the absorption and fluorescence spectra of Yb3+:ZrF4-BaF2LaF3-AlF3-NaF (ZBLAN) as input data, we employ a random-walk model to test analytical approximations of the fluorescence escape efficiency and cooling efficiency, including reflections at the boundary.