Electronic spectra and crystal field analysis of

The 10 K electronic absorption spectrum of Cs2NaTmF6 together with the 355 nm and 455 nm excited luminescence spectra of Cs2NaYF6:Tm3+ (1 and 10 at.% Tm3+) have been recorded and assigned in detail. Vibrational structure in the sidebands of the electronic transitions is analogous to that in the spectra of the hexachloroelpasolite systems except that the phonon dispersion is greater. The resulting 4f12 energy level dataset has been analyzed by a crystal field model including the configuration interaction with the ligand to metal charge transfer configuration. The previously published spectra of Rb2NaTmF6 and Rb2NaYF6:Tm3+ have been reinterpreted and shown to be consistent with the present results.