Optical and magnetic properties of the ground state of Cr3+ doping ions in REM3(BO3)4 single crystals.

New data about the state of Cr3+ doping ions in a single crystal of YGa3(BO3)4 have been obtained by studying different methods. Using electron paramagnetic resonance, it was found that the Cr3+ ions substitute the trivalent gallium ions. The obtained spin Hamiltonian parameters of the Cr3+ ions in the YGa3(BO3)4 single crystal (g = 1.9743 ± 0.0004; D = -0.465 ± 0.001 cm-1; E = -0.013 ± 0.001 cm-1) were analyzed and compared with those in TmAl3(BO3)4, EuAl3(BO3)4, and YAl3(BO3)4. The deviation of the Z-axis in the spectrum from the crystallographic axis С3 is 1,7 degrees in YGa3(BO3)4. In situ X-ray diffraction was used to study the structural and elastic properties of huntite-type borates in the temperature range of RT-1073 K. In the radioluminescence (RL) spectra, the Cr3+-related emission bands were observed in the red wavelength range, and the presence of other defect-related bands was also registered in some cases. Thermally stimulated luminescence (TSL) glow curves were acquired over a wide temperature range, and the trap depths of the most prominent bands were calculated. The 11B NMR spectra show that two nonequivalent spectral components exist for BO3 structural elements.

Study of the ground multiplet of Kramers rare earth ions in solid matrices by multifrequency electron paramagnetic resonance spectroscopy: Nd3+ in PbWO4 single-crystals.

A multifrequency electron paramagnetic resonance (EPR) investigation of Nd(3+) impurities in PbWO(4) single-crystals at the conventional microwave frequency (MF) 9.43 GHz, and at the 95, 190, and 285 GHz high frequencies was carried out. The resulting spectra are well described at all frequencies by an axial spin-Hamiltonian corresponding to an effective electron spin of one-half and to a tetragonal symmetry. For the magnetic field along the tetragonal axis, the g(parallel)-factor and the hyperfine constant A(parallel) of the lowest doublet of the ground multiplet decreases with frequency increase. For the magnetic field perpendicular to the tetragonal axis, the g(perpendicular)-factor exhibits a small azimuthal angular dependence that increases with increasing the frequency due to the S(4) site symmetry. The azimuthal angular dependence allows to clearly distinguish between different local axial symmetries. These properties are interpreted as high field/frequency (HF) effects associated with the mixing by the large Zeeman interaction of some of the upper-lying doublets of the ground multiplet into the lowest-lying doublet states. We show that from the combined analysis of the multifrequency MF- and HF-EPR spectra and of the optical data, an accurate description of the ground multiplet of the Kramers rare earth ions in solid matrices can be derived.

Peculiarities of excited state structure and photoluminescence in Bi(3+)-doped Lu(3)Al(5)O(12) single-crystalline films.

Single-crystalline films of Lu(3)Al(5)O(12):Bi, prepared by the liquid phase epitaxy method from the melt-solution based on Bi(2)O(3) flux, have been studied at 4.2-400 K by time-resolved luminescence spectroscopy methods. Their emission spectra consist of two types of bands with strongly different characteristics. The ultraviolet emission band consists of two components, arising from the electronic transitions which correspond to the [Formula: see text] and [Formula: see text] transitions in a free Bi(3+) ion. At low temperatures, mainly the lower-energy component of this emission is observed, having the decay time∼10(-3) s at T<100 K and arising from the metastable (3)P(0) level. At T>100 K, the higher-energy emission component appears, arising from the thermally populated emitting (3)P(1) level. The visible emission spectrum consists of two dominant strongly overlapped broad bands with large Stokes shifts. At 4.2 K, their decay times are ∼10(-5) s and decrease with increasing temperature. Both of the visible emission bands are assumed to have an exciton origin. The lower-energy band is ascribed to an exciton, localized near a single Bi(3+) ion. The higher-energy band shows a stronger intensity dependence on the Bi(3+) content and is assumed to arise from an exciton localized near a dimer Bi(3+) center. The origin and structure of the corresponding excited states is considered and the processes, taking place in the excited states, are discussed.

Structural and optical properties of Tb-doped Na-Gd metaphosphate glasses and glass-ceramics.

The optical and structural properties of terbium doped sodium gadolinium phosphate glasses of three different compositions subjected to a crystallization process were studied and compared with those of the parent glassy samples. The structural characteristics of the glassy and crystallized phases were determined by Raman spectroscopy and the results showed a remarkable reduction in the full width at half maximum of the Raman peaks after crystallization. Radio-luminescence measurements revealed the emissions of both Gd(3+) and Tb(3+) ions. Their intensities strongly increased and their intensity ratio was modified by the crystallization. The luminescence temperature dependence investigated by radio-luminescence measurements in the temperature interval from 10 to 310 K became more complicated after crystallization. The role of free carrier trapping phenomena in the modification of the radio-luminescence efficiency was also studied by thermally stimulated luminescence.

Defects creation under UV irradiation of PbWO4 crystals.

A systematic study of photothermally stimulated defects creation processes is carried out by the thermally stimulated luminescence (TSL) method for a large number of undoped and doped PbWO4 crystals under irradiation at 80-180 K in the 3.4-4.3 eV energy range. The activation energy Ea for the regular exciton state disintegration is found to be approximately 0.1 eV. For defect-related states disintegration, Ea varies in the crystals studied from 0.03 to 0.36 eV. The origin of the defect-related states is discussed. The conclusion is made that not only a release of charge carriers but also charge transfer processes take place under UV irradiation of PbWO4 crystals.

Slow relaxation, confinement, and solitons.

Millisecond crystal relaxation has been used to explain anomalous decay in doped alkali halides. We attribute this slowness to Fermi-Pasta-Ulam solitons. Our model exhibits confinement of mechanical energy released by excitation. Extending the model to long times is justified by its relation to solitons, excitations previously proposed to occur in alkali halides. Soliton damping and observation are also discussed.