Analysis of VUV and optical spectra of Cs2NaYF6 crystals doped with Tm3+

This study presents a detailed interpretation and analysis of the reported interconfigurational spectra of Tm3+ in Cs2NaYF6 [V.N. Makhov, N.M. Khaidukov, D. Lo, J.C. Krupa, M. Kirm, E. Negodin, Opt. Mater. 27 (2005) 1131]. Since only spin-forbidden d–f emission bands are observed for Tm3+ in this host, it is unsuitable for use as a scintillator because the emission lifetime is too long. The d–f emission spectrum is well-explained by calculation and most of the intensity is located in one band: 4f115d1 (high-spin) → 4f123H6. Measurements from the bands in the d–f excitation spectrum do not provide the accurate separation energy of the high and low-spin states. Strict Oh point group selection rules are operative for the optical spectra. The electronic states of the 4f115d1 configuration (briefly, d-electron states, hereafter) are calculated to span from 58,318 cm−1 to 86,900 cm−1. At least five structured bands are observed in the excitation spectrum and their intensities are fairly well simulated by calculation. The 4f12 → 4f13 (np6)−1 charge transfer band is assigned between 140 and 120 nm (∼83,000–71,000 cm−1) and excitation into this band leads to f–f emission, bypassing the d-electron states.