Influence of hydrostatic pressure upon the energy level scheme of Eu3+ in an La2O2S crystal

Abstract

The fluorescence spectra of Eu3+ in an La2O2S crystal have been measured at room temperature and under hydrostatic pressures up to 13 GPa. The pressure dependence of the energy levels of Eu3+ in La2O2S has been determined. The observed crystal-field levels shift upwards or downwards with increasing pressure and undergo a distinct change in shift rates at about 10 GPa. The relative shift rates of the observed centroids of 5D0-2 multiplets are about the same. Simulations of the observed energy levels of Eu3+ in Y2O2S crystals have also been carried out in order to make a comparison between the results for Y2O2S:Eu3+ and those for La2O2S:Eu3+. Of the six crystal-field parameters, only B02 shows a somewhat puzzling change with increasing pressure and decreasing internuclear distances due to different isomorphous hosts. In the pressure range up to 13 GPa, the Slater parameters F2, F4 and F6 show a decrease of 0.38(9)%, 0.38(0)% and 0.38(3)%, respectively; the spin-orbit coupling parameters zeta decreases by 0.20%. In order to understand the regular decrease in the 5D0-2 multiplets with increasing pressure, the authors have inspected the calculated free-ion energy levels under different pressures and found that the energy E of any excited level can be related to pressure P by E=E0(1-cP), in which c=2.90(+or-0.15)*10-4 GPa-1.