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Influence of Na+ and Pb2+ ions on the optical properties of Yb2+ ions in YbF3 doped CaF2 crystals
|Marius Stef , Irina Nicoara|
West University of Timisoara (UVT), Bd.V. Parvan nr.4, Timisoara 300223, Romania
The rare-earth ions can be stabilized in the divalent state in CaF2 lattice, besides the trivalent state, with which can coexist. It is known that certain fraction of Yb3+ ions can be reduced to divalent state by various methods  or directly in the as-grown crystals using high deoxidization growth conditions . The spectroscopic properties of the Yb2+ ions have been less investigated, mainly only for its intense and broad yellow-green luminescence .
The purpose of this work is to study the influence of Na+ and Pb2+ ions on the absorption and emission spectra of YbF3-doped CaF2 crystals with high divalent ytterbium content in the as-grown crystals.
NaF and PbF2 codoped Ca1-xYbx F2+x (x = 0.0007, 0.0017, 0.007, 0.0116) crystals have been grown using the conventional Bridgman technique . In order to obtain high Yb3+ - Yb2+ conversion a special procedure has been developed . Room temperature optical absorption spectra reveal the characteristic UV absorption bands of the Yb2+ ions. The presence of the Na+ ions drastically decrease the absorption intensity of the characteristic UV peaks of Yb2+ ions. The absorption peaks of the Pb2+ ions are in UV domain; the influence of these ions on the various Yb2+ ion peaks depends on the YbF3 concentration in CaF2. For low YbF3 concentrations the peaks intensity increases, for high concentrations decreases. The luminescence studies reveal a strong YbF3 concentration and codopant dependence of the near-UV emission bands. Besides the reported yellow-green luminescence, new emission bands have been observed in the near-UV spectral region. The Na+ ions drastically decrease the emission intensity of the characteristic UV peaks observed for the CaF2:YbF3 samples. The Na+ ions influence on the emission intensity depend on the λexcitation and on the NaF and YbF3 concentration. For the crystals codoped with Pb2+ ions the emission intensity increases in comparison with the CaF2:YbF3 samples. This effect depends on the YbF3 concentration and on the λexcitation. The observed emissions in the visible domain are attributed to the anomalous luminescence .
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Presentation: Poster at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, Topical Session 6, by Marius Stef
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17
Submitted: 2013-04-15 17:28 Revised: 2013-06-20 16:02