Anti-stokes luminescence in europium monochalcogenides

Anti-Stokes luminescence or up-conversion has been observed in the europium monochalcogenides. The emission occurs from localized regions in the crystals and may be assigned to transitions within the 4f⁶ configurations of Eu³⁺. In addition, we have studied the temperature and magnetic field dependence of the previously reported luminescence within the 4f⁷ configurations of Eu²⁺. The data show that its previous interpretation in terms of magnon sidebands is questionable. A mechanism requiring the presence of impurities or defects is proposed for the spin-flip transitions involved in both luminescence processes.