ИСТИНА

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/CO2 atmosphere, and 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 2F5/2 excited state of Yb3+ ions in the crystals.