Annina Aebischer, Oliver S. Wenger and Hans U. Güdel
Near-infrared to visible photon up-conversion in V³⁺, Re⁴⁺ co-doped Cs₂NaYCl₆
J. Lumin. 102-103, 48-53 (2003)                 

Abstract: Cs₂NaYCl₆ co-doped with V³⁺ and Re⁴⁺ was studied by optical absorption and luminescence spectroscopy. In the cubic host lattice both dopant ions substitute for the octahedrally coordinated Y³⁺. Visible by eye red up-conversion luminescence centered around 14 000 cm^–1 is observed upon near-infrared excitation within the energy range from 10 000 to 12000 cm^–1 between 15 and 300 K. For V^{3+ 3}T_2g excitation at 11 350 cm^–1, the efficiency of this up-conversion process increases with increasing temperature. An energy transfer step from V³⁺ to Re⁴⁺ followed by an energy transfer up-conversion process on the Re⁴⁺ system is shown to be the likely mechanism responsible for this phenomenon.