The search for novel non-linear optical materials for optoelectronics and laser engineering stimulates high interest of researchers to composite nanostructured systems. Composite materials based on crystalline matrixes with incorporated metal and metal oxide nanoparticles can be used in optical communication, optical computing, optical information processing etc. Earlier we have shown the prospects of the application of such composite materials in nonlinear optics on the example of KDP:TiO₂ crystals [1,2].

The present work studies peculiarities of the growth and structure formation of a new composite material based on KDP crystalline matrix with incorporated Al₂O₃·nH₂O nanoparticles. Pure KDP and KDP:Al₂O₃·nH₂O crystals were grown by temperature lowering method onto a point seed. The nanoparticles concentration in KH₂PO₄ solution varied from 0.1 to 100 ppm. It was established by means of transmission electron microscopy that the initial Al₂O₃·nH₂O nanofibres had a diameter of ~ 5 nm and a length of ~ 150 nm. After ultrasonic treatment the size and morphology of the nanofibers changed. The size of the particles incorporated into crystal matrix was found to be 11-40 nm.

As established, the  character of nanoparticle incorporation into the crystal matrix was selective. The dominant capture of the nanoparticles by the prismatic faces of KDP crystal was shown to be realized through the formation of hydrogen bonds. There was studied the interaction of Al₂O₃·nH₂O nanoparticles with the phosphate ions in KH₂PO₄ solution.  The model of the nanoparticles capture by the growing crystal face was proposed.

Structure investigations revealed the periodic distribution of the nanoparticles in the crystal bulk due to their accumulation at the crystallization front and the subsequent capture. The average period of striations was calculated. Variation of the nanoparticles concentration in the solution (within the limits of 1­-10 ppm) was shown not to affect essentially the period of zonal structure with an average value of about 4 mm.

The defect structure formation was investigated using the methods of selective etching and scanning electron microscopy. As found during this study, the incorporation of nanoparticles in the crystal matrix may be accompanied with the formation of liquid inclusions, or realized without the formation of defects. There were defined the optimum crystallization conditions providing the possibility to obtain the crystals with quasi-periodic distribution of the nanoparticles in the matrix without formation of defects. The periodic distribution of Al₂O₃·nH₂O nanoparticles in KDP crystals can be useful for creation of volume diffraction gratings and optical devices based on waveguide distribution of light.

[1] I. Pritula, V. Gayvoronsky, M. Kolybaeva et al., Optical Materials 33 (4) (2011) 623-630.

[2] V.Ya. Gayvoronsky, M.A. Kopylovsky, M.S. Brodyn et al., Laser Physics Letters 10 (2013) 035401-1–035401-5.

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