V. V. Mal’tsev

Optical properties of undoped and Yb3+-doped YAl3(BO3)4 crystals

The ordinary and extraordinary refractive indices of nominally undoped and Yb3+-doped (7 at %) YAl3(BO3)4 crystals have been measured in the visible range at temperatures from 20 to 400°C. The refractive indices are found to increase with temperature. The thermo-optic coefficients are on the order of ∼10−6. The temperature dependences of the refractive indices show a number of anomalies, suggestive of an incommensurate system exhibiting devil’s staircase behavior.

Infrared spectroscopy and the structure of rare-earth chromium borates RCr3(BO3)4 (R = La-Er)

Rare-earth chromium borates RCr3(BO3)4, where R = La-Er, obtained as a result of spontaneous solutionmelt crystallization and belonging to two polytypic modifications (R32 (D37) and C2/c (C2h6) space groups) are studied by infrared spectroscopy with the factor group analysis of vibrations. Borates with R = La-Nd are shown to crystallize in the monoclinic C2/c space group. Borates with R = Sm-Er in the 1:1 ratio of batch and solvent form rhombohedral (R32 space group) and monoclinic (C2/c space group) phases at the 2.3:1 ratio, except EuCr3(BO3)4 and GdCr3(BO3)4 that have the rhombohedral structure under all crystallization conditions. Both rhombohedral and monoclinic polytypes may contain oppositely ordered layers. Y-, Tm-, Yb-, Lu-chromium borates are not formed.

Energy transfer between Yb3+ and Er3+ ions in an Er,Yb:YAl3(BO3)4 crystal

The electron-excitation energy transfer between Er3+ and Yb3+ ions in Er,Yb:YAl3(BO3)4 crystals has been investigated. Crystals with different concentrations of active ions have been grown, and their luminescence decay kinetics in the spectral range near 1 μm have been experimentally measured. The energy-transfer microparameters have been calculated. It is shown that, to correctly describe the energy transfer in Er,Yb:YAl3(BO3)4 crystals, one must take into account the interactions of higher orders than dipole-dipole interactions.

Thermal stability of zincite single crystals

The effect of temperature on the stability of synthetic ZnO crystals in neutral (N2), oxidative (O2), and reductive (95% Ar-5% H2) media and in a low vacuum has been studied. In the first and second cases, zincite does not undergo changes up to 1000°C. After an 8-h exposure in oxygen at 1100°C, a decrease in the size of hexagonal growth hillocks on the monohedron face (0001) and smoothing of its relief on the whole have been observed. In the presence of hydrogen, etching traces manifest themselves on the crystal surface even at 760°C; further heating leads to their sublimation. The effect of annealing on the luminescence properties of zincite has been demonstrated.

Growth of (Er,Yb):YAl3(BO3)4 laser crystals

Abstract(Er,Yb):YAl3(BO3)4 single crystals of optical quality, up to 15 × 10 × 10 mm3 in size, have been grown from a (Er0.023Yb0.116Y0.862)Al3(BO3)4 solution in a Y2O3-B2O3-K2Mo3O10 melt. The initial borate concentration was 17 wt %, and the flux cooling rate increased from 0.08 to 0.12°C/h in the range 1060–1000°C. The physical properties of the single crystals grown are good enough that they can be used as laser elements in systems with diode pumping and radiation near 1.5 μm.

Recrystallization of natural chrysoberyl in multicomponent melts

Chrysoberyl and alexandrite crystals have been grown from solutions in melts based on the Li2CO3-MoO3, Bi2O3-MoO3, PbO-V2O5, Na2B4O7, and K2MoO4-MoO3 systems using natural alexandrite and chrysoberyl debris as the initial BeAl2O4 compound. An analysis of the morphology and homogeneity of the crystals grown has revealed the Bi2O3-MoO3 solvent to be the most appropriate. The optimal color characteristics (“quality” of alexandrite effect) manifest themselves when adding about 5 mol % Cr2O3. The largest crystals (up to 10 mm in size) were obtained from a solution in melt based on PbO-V2O5 at a ratio of the crystal-forming component to the solvent of 9: 91 wt %; These characteristics, along with a relatively low operating temperature (970°C), give grounds to consider this type of solvent promising.

Infrared spectroscopy of europium borates Eu M 3 (BO 3 ) 4 ( M = Al, Cr, Fe, Ga) with a huntite mineral type of structure

Huntite-like EuM3(BO3)4 crystals (M = Al, Cr, Fe, or Ga) are synthesized by means of spontaneous crystallization from a solution in a melt. The infrared spectra of the compounds are measured. The experimental data and the results from ab initio DFT calculations are compared. The comparison shows that the compounds have a primarily noncentrosymmetric rhomboherdal structure with the R32 space group. This indicates these compounds could exhibit magnetoelectric and nonlinear optical properties.

Effect of annealing on cathodoluminescence of synthetic zincite single crystals

We have studied the effect of annealing on the luminescent properties of zincite single crystals grown from hydrothermal solutions. Annealing in the temperature range of 400–700°C increases the edge cathodoluminescence (CL) intensity in zincite. At the same time, raising the annealing temperature from 800 to 1100°C leads to quenching of the edge emission and increases the intensity of the green band. In addition, annealing leads to broadening of the edge luminescence band and shifts it to lower energies. In contrast, annealing shifts the impurity band to higher energies. The observed changes in the CL behavior of zincite are tentatively interpreted in terms of the temperature effect on the concentration of structural defects, in particular, oxygen vacancies and their complexes.

Effect of flux composition on the morphology of KTiOPO4 crystals

KTiOPO4 crystals have been grown from flux of K6P4O13 in the presence of K2SO4, Li2SO4, and Na2SO4 salts and V, Cr, Ni, Co, Cu, Mo, Ba, Ce, Er, and W impurities. The crystals grown are characterized by well-developed simple {100}, {011}, and {201} faces. In some cases, new ({111} and (031)) faces arise. Some distortion of crystals caused by their pulling in the [101] direction is observed.