Th. Tröster

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...

A fluorescence study of Tb3+ doped tellurite glass under pressure

Fluorescence spectra and decay curves for the transition of Tb3+ ions in 59TeO2?20ZnO?20LiF?1Tb4O7?(TZLFTb) glass have been measured and analysed as a function of pressure up to 14.9?GPa at room temperature. In this pressure range, the red shift for the band positions of ,7F4 and 7F5 is found to be?3.2, 3.2 and 2.2?cm?1?GPa?1, respectively, which could be attributed to an expansion of the 4f?electron wavefunctions with increasing covalency. There is also a considerable pressure effect on the magnitude of the crystal-field splittings observed in the 7F4 and 7F5 transitions, which increases with pressure because of Coulomb interactions between the 4f electrons and their ligands. In addition, the decay curve is found to be perfectly single exponential at ambient pressure, and turns into a non-exponential with increasing pressure. The non-exponential decay curves at higher pressures are well fitted to the Inokuti?Hirayama model for S = 6, which indicates that the energy transfer between the donor and acceptor is of dipole?dipole nature. The decrease in the lifetime with increasing pressure is caused by an increase in the electronic transition probabilities, which is a result of the enhanced crystal-field strength around the Tb3+ ions. The results obtained after release of pressure show that local environment changes of the Tb3+ ions are reversible.

High-resolution site selective optical spectroscopy of rare earth and transition metal defects in insulators

Abstract Focusing on Er3+ ions in stoichiometric LiNbO3 we demonstrate the application of the combined excitation emission spectroscopy to defect systems with complicated multi-line spectra in insulating materials. After spectroscopic identification of the different defect types (“sites”) the changes under application of external perturbation (hydrostatic pressure, electric and magnetic fields) are investigated obtaining useful results about the electronic states. As a major result it is shown that even smallest spectral changes ( Δ E meV ) can be detected site selectively. In a similar way, the method has been applied to other defect systems.

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.

Study of the energy level scheme of under pressure

Excitation and luminescence spectra of in LaOCl were measured over the spectral range from to . At ambient pressure a total of 46 spectral lines could be observed. Under pressures up to 16 GPa, all lines exhibit a red-shift - however, with very different rates. From the spectral lines, the energy level scheme of the configuration could be partly derived. From 37 levels at ambient pressure, 30 could also be obtained under pressure. The energy level scheme is described by the use of free-ion ( (k = 2, 4, 6), ) and crystal-field parameters . According to the so-called nephelauxetic effect, the free-ion parameters and decrease under pressure. The magnitudes of the variations depend on the selected energy levels. Surprisingly the crystal-field strength shows a peculiar behaviour with an initial decrease and a minimum at 15 GPa. This behaviour can be explained within the context of the superposition model.

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.

High pressure fluorescence studies of Sm3+-doped K–Ba–Al phosphate glass

Pressure-induced fluorescence spectra and decay curves for the 4G5/2 level of Sm3+ ions in P2O5+K 2O+BaO+Al 2O 3 glass have been studied up to 24.4 GPa at room temperature. The study reveals that 4G5/2→6H J (J=9/2, 7/2 and 5/2) emission band positions are shifted to lower energy (red shift) in the order of 2.4, 2.6 and 2.7 cm−1 per GPa, respectively. The increase in Stark level splittings has also been noticed with increasing pressure for the emission bands mentioned above. The decay profiles show increased non-exponential behaviour at higher pressures accompanied by a shortening of lifetimes. The non-exponential decay curves were fitted to the Inokuti–Hirayama model. The decrease in the lifetime with an increase in pressure is caused by an increase in the electronic transition probabilities. This is a result of the increased crystal-field strength around Sm3+ ions. The original results obtained after the release of pressure confirm that no structural hysteresis takes place around the Sm3+ ions.

Effect of pressure on structure and fluorescence of SrFCL: Sm2+

Abstract Lattice parameters of SrFCl have been measured by powder x-ray diffraction up to 38 GPa. Furthermore, energy levels and crystal field parameters of Sm2+ in SrFCl have been determined from fluorescence spectra at 100 K under pressures up to 10 GPa.

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.

Spectroscopic Monitoring of the Eu 3+ Ion Local Structure in the Pressure Induced Amorphization Of EuZrF 7 Polycrystal

Amorphization is observed from the 5 D 0 M 7 F 0,1,2 emission spectra of the Eu 3+ ions in EuZrF 7 polycrystal measured at different pressures at room temperature. The crystalline phase progressively transforms to amorphous when the pressure is increased over 2 GPa. Compression of the EuZrF 7 crystalline phase results in an increase in the number of non-equivalent environments of the Eu 3+ ions with different crystal-field strengths. Simultaneously, an apparent loss of the long-range order, being typical for amorphous materials like glasses, can be observed, yielding similar emission spectra for the Eu 3+ ions as in the case of the fluorozirconate glasses. In these materials the local structure of the Eu 3+ ions is at least as low as the C S symmetry of the EuZrF 7 phase and their co-ordination number does not differ significantly from the eight-fold co-ordinated Eu 3+ ions found in the crystalline phase. Amorphization is retained after pressure release.