COMPARATIVE-STUDY OF THE CRYSTAL-FIELD EFFECTS IN RARE-EARTH OXYNITRATES

The photoluminescence spectra of the lanthanum and gadolinium oxynitrates doped with Eu3+, REONO3:Eu3+ (RE = La and Gd) were measured at 77 and 300 K. The F-7(J) (J = 0-5) energy level schemes for the 4f6 electron configuration were simulated by a C2nu phenomenological crystal field (CF). The nine non-zero CF parameters for the C2nu site symmetry reproduce the experimental energy level schemes with rms deviations of 7 and 5 cm-1 for the LaONO3 and GdONO3 hosts, respectively. The CF effect is stronger in the lanthanum host although otherwise the CF parameters for the two oxynitrate hosts differ only slightly. The B2k (k=2, 4 and 6) values are low indicating only a slight deviation from a higher C4nu symmetry. The B-0(2), B-0(4) and B-4(4) parameters assume high values which are similar to those obtained previously for the other RE oxy compounds, i.e. oxyhalides, oxysulfates, oxymolybdates, and oxytungstates. The sixth rank parameters deviate considerably from those obtained for the other RE oxy compounds.