Spectroscopic, laser, and chi((3)) nonlinear optical properties of tetragonal PbWO(4), NaY(WO(4))(2), CaWO(4), and monoclinic CdWO(4) and ZnWO(4) were investigated. Particular attention was paid to Nd(3+)-doped and undoped PbWO(4) and NaY(WO(4))(2) crystals. Their absorption and luminescence intensity characteristics, including the peak cross sections of induced transitions, were determined. Pulsed and continuous-wave lasing in the two 4F(3/2)-->4I(11/2) and 4F(3/2)-->4I(13/2) channels was excited. For these five tungstates, highly efficient (greater than 50%) multiple Stokes generation and anti-Stokes picosecond generation were achieved. All the observed scattered laser components were identified. These results were analyzed and compared with spectroscopic data from spontaneous Raman scattering. A new crystalline Raman laser based on PbWO(4) was developed for the chi((3)) conversion frequency of 1-microm pump radiation to the first Stokes emission with efficiency up to 40%. We classify all the tungstates as promising media for lasers and neodymium-doped crystals for self-stimulated Raman scattering lasers.

Scheelite-type compounds with the general formula (A1,A2)(n)[(B1,B2)O(4)](m) (2/3 ≤ n/m ≤ 3/2) are the subject of large interest owing to their stability, relatively simple preparation, and optical properties. The creation of cation vacancies (□) in the scheelite-type framework and the ordering of A cations and vacancies can be a new factor in controlling the scheelite-type structure and properties. For a long time, cation-deficient Nd(3+):M(2/7)Gd(4/7)□(1/7)MoO(4) (M = Li, Na) compounds were considered as potential lasers with diode pumping. They have a defect scheelite-type 3D structure (space group I4(1)/a) with a random distribution of Li(+)(Na(+)), Gd(3+), and vacancies in the crystal. A Na(2/7)Gd(4/7)MoO(4) single crystal with scheelite-type structure has been grown by the Czochralski method. Transmission electron microscopy revealed that Na(2/7)Gd(4/7)MoO(4) has a (3 + 2)D incommensurately modulated structure. The (3 + 2)D incommensurately modulated scheelite-type cation-deficient structure of Na(2/7)Gd(4/7)MoO(4) [super space group I4 (α-β0,βα0)00] has been solved from single-crystal diffraction data. The solution of the (3 + 2)D incommensurately modulated structure revealed the partially disordered distribution of vacancies and Na and Gd cations. High-temperature conductivity measurements performed along the [100] and [001] orientation of the single crystal revealed that the conductivity of Na(2/7)Gd(4/7)MoO(4) at T = 973 K equals σ = 1.13 × 10(-5) Ω(-1) cm(-1).

The high oxygen and lithium ion conductivity in LiNbO3 was investigated and interpreted in terms of lithium and oxygen vacancies being intrinsically present in congruently grown single crystals. As a result of this, it was found that the stoichiometry of lithium niobate crystals may be changed with respect to lithium and oxygen. The optical and electrical properties of electrically colored LiNbO3 crystals were studied and it was shown that the absorption spectra of thermally reduced and electrocolored samples are identical. Therefore, the origin of the absorption processes is considered to be the same in both cases. The formation of regions with different stoichiometry due to the injection of additional lithium or oxygen into the LiNbO3 crystals was also observed and investigated. The motion of these stoichiometric domains through a LiNbO3 crystal from one electrode to the other was studied and described in terms of electrodiffusion of the ions and electrons. A model is proposed which considers the injection of oxygen and lithium vacancies for the generation of concentration profiles in the originally homogeneous material. The numerical calculation of the concentration profiles shows good agreement with the experimental results.

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This study describes the influence of temperature on the structure and properties of KGd1−xEux(MoO4)2 (0 ≤ x ≤ 1).