Crystal field effect in RE3+-doped lanthanum oxycyanamide, La2O2CN2:RE3+(RE3+=Pr3+ and Eu3+)

The UV-vis-NIR absorption spectra of Pr3+ and the luminescence spectra of Pr3+ and Eu3+ in lanthanum oxycyanamide, La2O2CN2, were measured at selected temperatures between 10 and 150, and at 77 K, respectively. The whole 4f2 electron configuration of Pr3+ was accounted for in the simulation by a phenomenological crystal field (c.f.) model including 17 refinable parameters. For Eu3+, only the isolated 7F term of the 4f6 configuration was considered. The simulations were initially carried out in the C4v symmetry typical of the rare earth oxyhalides but the symmetry was subsequently lowered to C2v with four additional real c.f. parameters (B22, B24, B26 and B66) according to the descending symmetry method. The experimental energy levels were reproduced with satisfactory r.m.s. deviations of 18 (Pr3+) and 5 cm-1 (Eu3+) and no major discrepancies between the two energy level sets were observed. The La3+ site symmetry cannot thus be higher than C2v, but it is only slightly distorted from the C4v symmetry as indicated by the low values of the four additional c.f. parameters for both RE3+ ions. The results for Pr3+ and Eu3+ are mutually consistent as well as with the RE oxychlorides and other RE oxycompounds. (orig.)