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

The fluorescence spectra of Eu 3+ in an La 2 O 2 S crystal have been measured at room temperature and under hydrostatic pressures up to 13 GPa. The pressure dependence of the energy levels of Eu 3+ in La 2 O 2 S 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 5 D 0-2 multiplets are about the same. Simulations of the observed energy levels of Eu 3+ in Y 2 O 2 S crystals have also been carried out in order to make a comparison between the results for Y 2 O 2 S:Eu 3+ and those for La 2 O 2 S:Eu 3+ . Of the six crystal-field parameters, only B 0 2 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 F 2 , F 4 and F 6 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 5 D 0-2 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=E 0 (1-cP), in which c=2.90(+or-0.15)*10 -4 GPa -1 .