Electronic spectra of Yb3+in elpasolite lattices

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Abstract
Intense luminescence due to the 2 F 5/2→2 F 7/2 transition, near 1μm, is observed when the elpasolites Cs2NaHoCl6 and Cs2NaNdCl6 are doped with Yb3+ and excited by 488 nm or 514 nm argon ion laser radiation respectively. The mechanism of energy transfer has been studied for Cs2NaHoCl6: YbCl3- 6 using temperature, concentration and kinetic studies, and involves a cross-relaxation from 5 F 5(HoCl3- 6). The liquid-helium-temperature luminescence spectra are interpreted, and together with the absorption spectrum of Cs2NaYbCi6 all of the f 13 energy levels are assigned. The agreement with the latest crystal field calculations is poor. A comparison is made with the luminescence and excitation spectra of Cs2NaHoBr6: YbBr3- 6. No luminescence from YbCl3- 6 at a site of octahedral symmetry is observed in Yb3+-doped Cs2NaTmCl6 or Cs2NaErCl6. In the former case the closest level is about eight phonons above 2 F 5/2 so that the Yb3+ level is not appreciably populated, and in the latter case the 4 I 11/2(ErCl3- 6) levels are located just below, and hence depopulate 2 F 5/2.