Phonon-assisted anti-Stokes excitation of the fluorescence of Mn 2+ ions in the CsMnCl 3 ⋅2H 2 O crystal

We demonstrate that anti-Stokes excitation of Mn 2+ ions in the CsMnCl 3 ⋅2H 2 O crystal can occur through multiphonon addition to the energy of the photons of exciting light. The deficit dE between the energy of the Mn 2+ 4 T 1 exciton and the photon energy of the He–Ne laser used as the source of illumination is compensated by simultaneous annihilation of several thermally activated lattice phonons. The absence of two-photon activation of the fluorescence was verified by measurement of the dependence of the fluorescence intensity on the intensity of the exciting light, which appears linear at a fixed energy mismatch dE.