Down-Conversion Luminescence of Yb3+ Ions in Yb:CaWO4 Single Crystals

Ytterbium and ytterbium -niobium doped sheelite single crystals have been grown by the Czochralski method in air and in protective atmospheres and subjected to additional annealing in air, in CO/CO
2
atmosphereand in forevacuum. Comparative investigations of optical absorption and photoluminescence spectra of the crystals in the visible and near-IR spectral regions upon UV excitation were performed. A consistent pattern is proposed, explaining the nature of the donor centers involved into the process of down-conversion population of
²
F
5/2
excited state of Yb
³
+ ions in the crystals.