Yu. K. Voron’ko

Raman spectroscopic study of structural disordering in YVO4, GdVO4, and CaWO4 crystals

The Raman spectra of single-crystal YVO4, GdVO4, and ZrSiO4 with a zircon structure, as well as CaWO4 and BaWO4 with a scheelite structure, are studied in detail over a wide temperature range 14–800 K. An inhomogeneous splitting of the A1g(ν2) vibrational lines in the Raman spectra of YVO4 and GdVO4 and the Ag(ν1) vibrational lines in the spectrum of CaWO4 is detected. It is shown that the profiles of these lines can be decomposed into two components, whose integrated intensities are redistributed with temperature and also depend on the matrix kind in which they are detected. The phenomenon observed is associated with the thermally activated processes of disorientation of the tetrahedral anions in the zircon and scheelite structures.

Lead borate oxyfluoride glasses doped with Nd 3+ ions and transparent glass–crystal materials based on them

This paper discusses the properties of synthesized lead borate oxyfluoride PbF2–PbO–B2O3 glasses doped with Nd3+ ions at concentrations from 0.6×1020 to 25×1020 cm−3. The possibility of using them as a basis for obtaining transparent glass–crystal materials by controlled crystallization with precipitation of the fluoride crystalline phase is studied. The changes in the structure and optical properties of the glass–crystalline material by comparison with the initial glasses were monitored by X-ray phase analysis and Raman spectroscopy and by investigating the fluorescence characteristics of the Nd3+ ions.

Growth and spectroscopic studies of NaLa(MoO4)2:Tm3+ crystals: A new promising laser material

Single crystals of scheelite-like disordered double molybdate NaLa(MoO4)2 doped with thulium ions with dopant concentrations of 3.0 × 1019 and 1.2 × 1020 cm−3 are grown by the Czochralski method. Spectral and luminescent studies of crystals grown are performed in wavelength ranges of 800 nm (the transitions 3H6↔3H4) and 2 μm (the transitions 3H6↔3F4), including the measurements of the polarized absorption and luminescence spectra of these crystals and the decay kinetics of their excited states. A model that satisfactorily describes the decay kinetics of the luminescence from the 3H4 level taking into account cross-relaxation interactions is proposed. The prospects for the use of these crystals as active media in two-micrometer solid-state lasers are discussed.

Structural transformations in LiGd9(SiO4)6O2 and Ca2Gd8(SiO4)6O2 crystals containing isolated [SiO4] complexes: Raman spectroscopic study

The vibrational spectra of single crystals of the LiGd9(SiO4)6O2 and Ca2Gd8(SiO4)6O2 oxyapatites have been studied using Raman spectroscopy at room and high temperatures. The spectra of internal and external vibrations in these structures have been resolved. The structural transformation of the LiGd9(SiO4)6O2 and Ca2Gd8(SiO4)6O2 oxyapatites in the processes of melting and crystallization, as well as during rapid quenching of the melt, has been investigated. It has been found that the melting of the LiGd9(SiO4)6O2 compound has an incongruent character and that new metastable disordered phases are formed during rapid quenching of the Ca2Gd8(SiO4)6O2 melt.

Intensity parameters for Er3+ ions in calcium-niobium-gallium garnet crystals

Based on the analysis of the absorption spectra of Er-doped calcium-niobium-gallium garnet (Er:CNGG) crystals according to the Judd-Ofelt theory, the intensity parameters for these crystals are determined to be Θ2 = 3.43 × 10−20 cm2 Θ4 = 1.20 × 10−20 cm2, and Θ6 = 0.58 × 10−20 cm2. The parameters found are compared with the intensity parameters for other laser oxide crystals. Using these intensity parameters, the probabilities of radiative transitions between the energy levels of Er3+ ions in CNGG crystals and the luminescence branching ratios βJJ’ are calculated. From the measured lifetime of the 4I11/2 level of Er3+ ions (τ = 626 μs) and the probability of the radiative transition from this level (A = 192 s−1), it is found that about 88% of the excitation energy in the Er:CNGG crystals is nonradiatively transferred from the 4I11/2 to the 4I13/2 level. It is suggested that an increase in the oscillator strength and in the line strength of the 4I15/2 → 2H11/2 transition of Er3+ in CNGG crystals, as well as an increase in the intensity parameter Θ2 with respect to the corresponding parameters for other garnet crystals are caused by the existence in CNGG crystals of Er3+ centers with the environment symmetry lower than D2.

Synthesis and spectroscopy of sodium-gadolinium tungstate NaGd(WO4)2 crystals activated by Tm3+ ions

Single crystals of disordered double sodium-gadolinium tungstate NaGd(WO4)2 doped with Tm ions were grown by the Czochralski method. The polarized absorption and emission spectra of these crystals with different activator concentrations and the decay kinetics of the 3H4 and 3F4 excited states of Tm3+ ions at 300 K were investigated. The absorption and emission cross sections of the expected laser transition 3F4 ↔ 3H6 in the Tm3+ ion were determined and the amplification spectra of the active laser medium NaGd(WO4)2:Tm at different levels of inverse population of the upper laser level 3F4 of the Tm3+ ion were constructed. The prospects for using these crystals as active media in 2-μm solid-state lasers are discussed.

Raman scattering in LiB3O5 single crystals at 300 and 20 K

The Raman-scattering spectra of LiB3O5 single crystals at 300 and 20 K have been investigated in detail. The LO- and TO-phonon lines of different symmetries are separated and identified. The reasons for the change in the Raman spectra of LiB3O5 upon cooling to 20 K are studied. The intensity ratios for scattering with participation of LO and TO modes of the A1 symmetry are found in dependence on the observation geometry.

Spectroscopy of NaLa(MoO4)2: Tm3+ and NaGd(MoO4)2: Tm3+ crystals as advanced laser materials

Single crystals of double sodium-containing lanthanum and gadolinium molybdates doped with Tm3+ ions were synthesized by the Czochralski method. The spectroscopic properties of these crystals were investigated from the viewpoint of their use as active media in diode-pumped lasers. The polarized spectra of absorption on the 3H4 and 3F4 levels and the polarized spectra of luminescence due to the 3F4-3H6 laser transition were recorded, and the lifetimes of the 3H4 and 3F4 excited states of the Tm3+ ions were determined. The luminescence cross sections were calculated using the Füchtbauer-Ladenburg formula. The simulation of the decay curve of the 3H4 excited state according to the Golubov-Konobeev-Sakun method revealed that, in the crystals under investigation, the interaction between Tm3+ ions predominantly occurs through the dipole-dipole mechanism.

Spontaneous Raman scattering of Lu2Si2O7 single crystals at temperatures in the range from 20 to 2173 K

Detailed studies of the polarized Raman spectra of lutetium pyrosilicate single crystals have been performed in a wide temperature range from 20 to 1500 K. This has made it possible for the first time to identify the entire set and symmetry of the internal vibrations of the [Si2O7]6− anion and the lattice vibrations of this compound. The Raman spectra of the lutetium pyrosilicate have been investigated in the temperature ranges preceding the melting, the molten state, and the overheated melt of the compound up to 2173 K. The Raman spectra of lutetium pyrosilicate single-crystal microregions have been studied in order to elucidate the nature of defect inclusions in their bulk.

Spectral diagnostics of vapor composition over molten Na2WO4 and Na2O-BaO-B2O3 system

The high-temperature Raman spectra recording technique was found applicable also to study luminescence of atoms and individual molecular groups in vapors over some overheated molten compounds. Sodium atomic luminescence excited with a yellow (578.2 nm) copper vapor laser line was detected in vapors over overheated molten Na2WO4 and Na2O-BaO-B2O3 system. The possibility of recording the sodium doublet spectrum by excitation with the 578.2 nm copper vapor laser line in vapors of any melts containing sodium was shown. Overheated melts in the Na2O-BaO-B2O3 system disproportionate and lose boron oxide as evidenced by the recording of luminescent spectra of BO2 molecular radicals in vapors over relevant melts.