Electronic Spectra of Cs2NaYbF6 and Crystal Field Analyses of YbX63- (X = F, Cl, Br)

Detailed analysis of the vibronic structure in the electronic absorption spectrum of Cs2NaYbF6 at temperatures between 10 and 300 K enables the crystal field energy level diagram of Yb3+ in this cubic host to be deduced. Ultraviolet and visible laser excitation of Cs2NaYbF6, Cs2NaY(0.9)Yb(0.1)F6, and Cs2NaHo(0.99)Yb(0.01)F6 give spectral features mainly due to Yb3+ being situated at a range of defect sites. The 4f13 crystal field analyses of octahedral YbX6(3-) (X = F, Cl, Br) systems show the expected trends in parameter values, but the energy level fits are poor. Inclusion of the interaction with the charge-transfer configuration 4f14np5 provides an exact fitting of energy levels for YbX6(3-), and a smooth variation of ff and fp crystal field parameters for Cs2NaLnCl6 (Ln = Er, Tm, Yb) is observed.