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Single crystals of KDP crystals with embedded Urea molecules and TiO 2 nanoparticles have been grown from aqueous solution by the temperature lowering method. The effect of the organic molecules and nanoparticles on the structural and mechanical properties has been studied. It has been observed that addition of Urea molecules improves laser induced damage threshold and mechanical strength of the crystal, while TiO 2 nanoparticles have the opposite effect. The structure and composition of KDP:Urea crystal are studied by three-crystal X-ray diffraction analysis, which reveals the existence of a correlation between the increase of the microhardness value and the change of the crystal lattice parameter. The surface features of KDP:TiO 2 crystals are analyzed by scanning electron microscopy that reveals the presence of quasi-equidistant growth bands caused by capture of the nanoparticles. It is shown that the rise of TiO 2 nanoparticles concentration up to 10 −4 wt.% and higher resulted in 3-fold reduction of the laser damage threshold of KDP:TiO 2 relative to pure KDP in [001] and [100] crystallographic directions. It is found that microhardness and fracture toughness decrease at the nanoparticles concentration of 10 −3 wt.% due to crack formation at crystal lattice discontinuities. The grown crystals also have been subjected to dielectric studies.

Potassium dihydrogen phosphate (KDP) crystals doped with xylenol orange (XO) and methylthymol blue (MTB) are grown from aqueous solutions by the method of solvent evaporation at room temperature under the conditions of natural convection and by the method of temperature lowering. Studied is the influence of the mother solution acidity on the character of the crystal coloration. The color and coloration intensity of the grown crystals are shown to strongly depend on the solution's pH. It is revealed that the crystal habit changes in the presence of organic dyes. The optical transmission spectra and the luminescence spectra of KDP:XO solutions and of the grown crystals are measured. The effect of thermal treatment and UV-irradiation on the coloration stability of the crystals is studied. It is found that the laser damage threshold in the prismatic impurity rich colored sectors of KDP:XO is the same as that in the prismatic sectors of pure KDP crystals.

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The ESR (electron spin resonance) investigation of two types of an oxygen hole center in -irradiated DKDP (KD 2 PO 4 ) single crystals is carried out. The room temperature spin-Hamiltonian constants are determined. The origin of the oxygen hole centers is discussed.