Anti-Stokes fluorescent cooling by energy transfer

A new model on the mechanism of anti-Stokes fluorescent cooling is proposed, based on which incident laser induces a phonon-assisted energy transfer from one luminescent center to another in an optical medium and causes medium cooling when the energy transfer is an anti-Stokes process and absorbs phonons. Here, we develop the model in two cases: two-phonon-assisted energy transfer for a small energy mismatch and one-phonon-assisted energy transfer for a large energy mismatch. The dependence of relative cooling efficiency on photon energy and temperature is also discussed in evaluating the new mechanism.