Spontaneous temperature and fluorescence oscillations in CaS:Eu2+ crystals excited in the long-wavelength tail of the absorption spectrum

摘要

The electric dipole allowed 4f(6)5d(1)-f(7) fluorescence of CaS:Eu2+ crystals was studied under excitation in the long-wavelength tail of the absorption spectrum (the regime typical for laser cooling experiments). Though no actual cooling was detected, spectra with a strong anti-Stokes component were observed which demonstrate the possibility to employ electron-phonon bands of electric dipole allowed transitions for optical refrigeration. Under the strong laser excitation, the heating of thermally-isolated crystals was observed accompanied by optical bistability and spontaneous fluorescence oscillations. These unusual effects in fluorescence are ascribed to strong nonlinearities existing in the system. (C) 2015 Elsevier B.V. All rights reserved.