Divalent rare-earth ions in LaF3 crystals
The optical spectra and electric conductivity of LaF3 crystals doped with 0.01, 0.1, and 0.3 mol % YbF3, where Yb was partly or completely recharged to the divalent state, are studied. The long-wavelength absorption band of 370 nm is caused by electrons transitioning from state 4f 14 to the level of anion vacancies. The remaining bands at 300–190 nm are caused by 4f 14–5d 14f 13 transitions in Yb2+. The bulk electric conductivity and peaks of the dielectric losses of LaF3–Yb2+ crystals are caused by Yb2+–anion vacancy dipoles. The activation energy of the reorientation of Yb dipoles is 0.58 eV. The optical and dielectric properties of Yb2+ centers are compared to those of Sm2+ and Eu2+ centers studied earlier in LaF3 crystals.
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