Crystal fields in ROF:Tb3+ (R = La, Gd)

Abstract

Laser excited luminescence and site selective excitation spectra of trivalent terbium (Tb3+) in two rare earth oxyfluoride (ROF) matrices, LaOF and GdOF, were detected at temperatures down to liquid helium. From the analyses of spectra, the crystal field (c.f.) fine structure of the 7FJ (J=0–6) ground multiplet was obtained for the 4f8 electron configuration. The energy level schemes comprising 26 c.f. sublevels out of 33 allowed for the C3v point symmetry of the R3+ site were simulated according to a phenomenological model taking into account only the c.f. effect.The simulation including six c.f. parameters (B02, B04, B34, B06, B36, and B66) reproduced the experimental energy level schemes in a satisfactory manner with rms deviations of 5 and 6cm−1 for the LaOF and GdOF hosts, respectively. The c.f. parameter sets are characterized by B02 values close to zero while the fourth and sixth rank parameters assumed rather high values. The Oh to C3v descending symmetry method revealed a slight trigonal distortion from the cubic fluorite CaF2-type structure. The c.f. parameters vary only slightly as a function of the host matrix. The 7F6 level was not simulated correctly probably because of the electron–phonon interaction.