Влияние способа сильного легирования на композиционную однородность и оптические свойства монокристаллов LiNbO-=SUB=-3-=/SUB=- : Mg

Raman spectroscopy, laser conoscopy and photoinduced light scattering methods have been applied to comparatively study composition uniformity of strongly doped LiNbO3 crystals with a magnesium concentration close to a threshold value ≈5 mol% MgО, grown from a charge synthesized using precursor Nb2O5:Mg (homogeneous doping method) and at direct addition of magnesium to the melt (direct doping method). It has been shown that application of homogeneous doping method allows one to obtain compositionally more homogeneous heavily doped LiNbO3:Mg crystal than direct melt doping method.

Дефекты и некоторые физические свойства номинально чистых и легированных цинком кристаллов ниобата лития

The features of defect structure and their influence on the properties of LiNbO3:Zn crystals, doped in a wide concentration range, including two concentration thresholds (at ~ 3.0 and ~ 6.8 mol. % ZnO in the melt), were studied by absorption IR spectroscopy in the region of OH--group valence vibrations, photoluminescence in the visible region of the spectrum, and photoinduced light scattering. In LiNbO3:Zn(0.004-2.01 mol. % ZnO) crystals the increase of zinc concentration led to increasing in the OH--group concentration and decreasing the luminescence intensity of luminescence centers associated with NbLi defects. Apparently, the latter was connected with the formation of small energy levels near the bottom of the conduction band as the zinc atoms displaced niobium atoms from the lithium positions in the ideal structure and the NbLi defect concentration decreased, respectively. In highly doped LiNbO3:Zn crystals (4.46-6.5 mol. % ZnO) and in the LiNbO3stoich(6.0 wt. % K2O) crystal there were lower OH--group concentration, the increase of band gap by 0.3-0.4 eV, and the increase of luminescence intensity in the green region of the spectrum due to the formation of new recombination channels compared to weakly doped crystals. In addition, in such crystals, the increase of proton conductivity was observed due to increasing in the concentration of interstitial hydrogen H+ and, as a result, the formation of many small acceptor levels near the valence band.

Structural particularities and optical properties of lithium niobate single crystals grown from the charge doped by boron.

The analysis of structural particularities and optical properties of LiNbO3 : B (0,55, 0,69 and 0,83 mol. % B2O3) was performed by methods of Raman and photoinduced light scattering, infrared absorption and laser conoscopy. It has been established that the boron impurity brings to 1 the distribution coefficient of lithium and niobium in the growing process. Thus, LiNbO3: B crystals grown from a congruent melt approach the stoichiometric crystals in ordering the structural units of the cation sublattice and the Li / Nb ratio.

Influence of trace amounts of boron on structural defects of lithium niobate crystal.

The analysis of structural particularities of nominally pure LiNbO3 : B grown with using of B2O3flux was performed by methods of Raman and photoinduced light scattering, infrared absorption andlaser conoscopy. It was established that the non-metallic element boron is included in the vacant tetrahedrals of LiNbO3crystal structure at trace amounts. In this case, boron substantially deforms the oxygen octahedra of the structure and changes their polarizability. It affects the nonlinear optical properties of the crystal. Boron, as an active complexing agent, structures the melt and aligns value of the distribution coefficients of lithium and niobium in the growing process. Boron in the tetrahedralsreduces both the number of NbLidefects and the content of multiply charged uncontrolled impurities in the crystal, enhancing the optical damage.

Photoinduced light scattering and photoelectric fields in zinc doped lithium niobate crystals.

Nominally pure and doped with zinc in a wide concentration range lithium niobate crystals were studied using photoinduced light scattering. Using the parameters of photo-induced scattered light, we determined the values of the photovoltaic and diffusion field intensities in lithium niobate crystals of different compositions. It was found that the values of thephotoelectric field strengths depend on the state of the defect structure of the crystals.

Kinetic Dependencies of the Photorefractive Effect in Lithium Niobate Crystals

The kinetic dependence of the photorefractive effect in the congruent lithium niobate crystal is determined in the work. The adequacy of the model for calculating the photoelectric fields from the indicatrix of photoinduced light scattering is shown. Two methods for determining the induced birefringence by interferograms and on the parameters of photoinduced light scattering are compared.