W. Sievers

High-pressure fluorescence study of Sm3+-doped borate and fluoroborate glasses

Fluorescence spectra and decay properties of the G5∕24 level of the Sm3+ ions have been measured in two glass systems of lithium borate and lithium fluoroborate glasses as a function of pressure up to 27.2 and 25.9 GPa, respectively, at room temperature. With an increase in pressure continuous redshifts of the G5∕24→HJ6 (J=9∕2,7∕2, and 5∕2) multiplet transitions as well as progressive increases in the magnitude of the splittings for these transitions are observed. Decay curves in both the systems exhibit perfect single exponential behavior at ambient pressure and become nonexponential at higher pressures accompanied by a moderate decrease in lifetimes. The nonexponential decay curves fit well to the Inokuti–Hirayama [M. Inokuti and F. Hirayama, J. Chem. Phys. 43, 1978 (1965)] model for S=6, indicating that the interaction for cross relaxation is of dipole-dipole type. The decrease in lifetime of the G5∕24 level in both the systems with pressure is explained as resulting from the increase in the crystal-fi...

Pressure dependent luminescence properties of Eu3+: TeO2-K2O-Nb2O5 glass

Eu3+-doped tellurite glass of molar composition: TeO2 + K2O + Nb2O5 + Eu2O3 (TKN1Eu) has been prepared by quenching the oxidic melts. The emission spectra and the decay curves for the 5D0 level of Eu3+ ions in TKN1Eu glass have been measured and analyzed as a function of pressure up to 14.8 GPa at room temperature. In this pressure range, the observed red shifts for the band positions of 5D0 → 7F0, 1, 2 could be attributed to an expansion of the 4f electron wave functions with increasing covalency. There is also a considerable pressure effect on the magnitude of crystal-field (CF) splitting in the 5D0 → 7F1 band, which increases with pressure. Stark components of the 7F1 level have been used to evaluate the CF parameters, B20 and B22, which are in turn used to calculate the CF strength experienced by the Eu3+ ions in the TKN1Eu glass. The CF strength increases from 1062 to 1358 cm-1 from the ambient pressure to 14.8 GPa. Lifetime for the 5D0 level of Eu3+ is found to decrease from 0.76 ms (0 GPa) to 0.30 ms (14.8 GPa) with increase in pressure. The results of pressure induced energy shifts, CF strengths and lifetimes are well discussed both for increasing as well as decreasing pressures and are compared with those of Eu3+: phosphate and lithium borate glasses.

Role of the local structure and the energy trap centers in the quenching of luminescence of the Tb3+ ions in fluoroborate glasses: a high pressure study.

The concentration and pressure dependent luminescence properties of the Tb(3+) ions in a lithium fluoroborate glasses have been studied by analyzing the deexcitation processes of the (5)D(4) level at ambient conditions as well as a function of pressure up to 35 GPa at room temperature. The luminescence spectra of Tb(3+) ions have been measured as a function of pressure and observed a continuous redshift as well as a progressive increase in the magnitude of the crystal-field splittings for the (5)D(4)-->(7)F(3,4,5) transitions. Monitoring the (5)D(4)-->(7)F(5) transition, the luminescence decay curves have been measured and analyzed in order to understand the dynamics of the deexcitation of the Tb(3+) ions in these glasses. At ambient conditions a nonexponential behavior has been found for doping concentrations as low as 0.1 mol % of Tb(4)O(7), although no cross-relaxation channels exist to explain this behavior. The modelization of the energy transfer processes surprisingly shows that the nonexponential character of the decay curves of the (5)D(4) level with concentration or with pressure has to be ascribed to energy transfer to traps without migration of energy between Tb(3+) ions. For all the experimental situations the nonexponential character of the decay curves is well described by the generalized Yokota-Tanimoto model with a dipole-dipole interaction between the Tb(3+) ions and the nearby luminescence quenching traps. The luminescence properties observed with releasing pressure are slightly different to those obtained while increasing pressure suggesting a local structural hysteresis in the lithium fluoroborate glass matrix giving rise to the generation of a new distribution of environments for the Tb(3+) ions.

Pressure dependent luminescence properties of Sm3+ ions in fluorophosphate glass

Pressure dependent luminescence spectra and decay curves for the 4G5/2 level of Sm3+ ions in fluorophosphate glass of composition 55.975 P2O5 + 14 K2O + 6 KF + 14.975 BaO + 9 Al2O3 + 0.05 Sm2O3 (referred as PKFBASm005) have been measured as a function of pressure up to 40.2 GPa. In this pressure range, the red-shift (during increase in pressure), the blue-shift (while releasing pressure) and enhanced crystal-field splitting with increase in pressure are observed for 4G5/2 → 6HJ (J = 9/2,7/2 and 5/2) multiplet transitions of PKFBASm005 glass. These pressure induced shifts as well as crystal-field splittings were explained by the interaction of Sm3+ ions with its surrounding ligands under pressure. The decay curves for the 4G5/2 level are found to be non-exponential in the entire pressure range. The lifetime for the 4G5/2 level decreases from 3.23 to 1.62 ms with increase in pressure from ambient to 40.2 GPa. The generalized Yokota-Tanimoto (YT) model has been used to explain non-exponential behaviour of decay curves.

Pressure-dependent fluorescence studies of Sm3+-doped fluorophosphate glass

Pressure-induced luminescence spectra and decay curves for the 4G5/2 level of Sm3+ ions in fluorophosphate glass (PKFBASm 40:54 P2O5+14 K2O+13 BaO+6 KF+9 Al 2 O 3+4 Sm 2O 3) have been measured as a function of pressure up to 36.3 GPa at room temperature. In this pressure range, a red shift of barycenter and Stark level splittings are observed for the 4G5/2→6HJ (J=9/2, 7/2 and 5/2) multiplet transitions. The decay curves of the 4G5/2 level show non-exponential behavior in the entire pressure range, which has been explained by energy transfer due to the dipole–dipole interaction. The effect of releasing pressure on the luminescence spectra and decay curves has also been studied. The results obtained for this glass have been compared with Sm3+-doped fluorophosphate, phosphate, lead phosphate, lithium borate and tellurite glasses.