| Autor: |
Subbotin, K. A., Titov, A. I., Lis, D. A., Chernova, E. V., Lis, O. N., Smirnov, V. A., Zharikov, E. V., Shcherbakov, I. A. |
| Zdroj: |
Physics of Wave Phenomena; Jul2021, Vol. 29 Issue 3, p187-198, 12p |
| Abstrakt: |
Yb:CaWO4 and Yb, Nb:CaWO4 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. The optical absorption spectra in the range from 250 to 1500 nm and the luminescence spectra of these crystals in the visible and near-IR spectral regions upon UV excitation have been investigated. It is shown that additional introduction of Nb5+ ions into Yb:CaWO4 crystal increases by an order of magnitude (almost to unity) the Yb3+ distribution coefficient between CaWO4 crystal and melt. It is found that optical excitation of the crystals in the range of 260–355 nm induces down-conversion luminescence of Yb3+ ions from the 2F5/2 level in the vicinity of 1 µm. An increase in the oxidative potential of synthesis atmosphere, as well as the introduction of niobium into the crystal composition, weakens this luminescence. A consistent pattern explaining the nature of the donor centers involved in down-conversion population of excited state 2F5/2 of Yb3+ in the crystals is proposed. Within this pattern, Yb2+ ions play the role of these donor centers. Another (much less efficient) mechanism of population of the 2F5/2 level is intracenter relaxation from the higher-lying charge transfer excited state within Yb3+ ions. At the same time, it is confirmed that color centers based on oxygen vacancies and partially reduced tungsten ions, as well as self-trapped excitons on tungstate complexes, are not involved in population of the excited state 2F5/2 of Yb3+ ions, and the optical centers formed in Yb:CaWO4 crystals as a result of vacuum annealing suppress ytterbium luminescence. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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