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Anti-Stokes laser cooling in Yb3+-doped KPb2Cl5 crystal

We report internal laser cooling in Yb3+ doped KPb2Cl5 crystal. From the quantum efficiency values measured in the heating and cooling regions by using the photothermal deflection technique, we have obtained a room temperature cooling efficiency of 0.2% in a sample doped with about 5 x 1019 ions/cm3. Excitation spectra obtained under high irradiation fluences show an excess of fluorescence with regard to those obtained at low fluences, which agrees with the prediction of a model based on the photon-ion-phonon interaction.