O.N. Bezkrovnaya

Macroscopic and microscopic defects and nonlinear optical properties of KH2PO4 crystals with embedded TiO2 nanoparticles

Results from the successful growth of high quality KH2PO4 (KDP) crystals with incorporated TiO2 anatase nanoparticles and the characterization of these crystals using several complementary methods are presented. The study allowed the nature and distribution of macroscopic and microscopic defects in the KDP:TiO2 crystals to be clarified. The relationship between these defects and the distribution of TiO2 nanoparticles, and the influence of incorporated nanoparticles on the nonlinear optical properties of composite crystals in comparison with pure crystals were also elucidated. Visual observations, transmission and scanning electron microscopy have shown that the anatase nanoparticles were captured mainly by the pyramidal growth sector and, to a considerably lesser extent, by the prismatic growth sector. Energy dispersive x-ray analysis was able to confirm that the growth layer stacks contain the TiO2 particles. Fourier transformation infrared spectra have clearly shown the presence of an absorption band at...

Paramagnetic defects in KH2PO4 crystals with high concentration of embedded TiO2 nanoparticles

Qualitative transformations of spectra of Electron Paramagnetic Resonance, EPR, were found in KH2PO4 crystals grown from liquor with 10−5–10−1 wt. % of anatase TiO2 nanoparticles in comparison with nominally pure KH2PO4. The nanoparticles have larger segregation coefficient for prismatic parts of the crystals than for pyramidal ones. Significant decrease in resonance absorption, complete disappearance of EPR lines of Fe3+ and Cr3+ centers, and appearance of four weak lines of equal intensities together with broad asymmetric lines with g-factors about 2.07–2.5 was observed in pyramidal parts grown with concentration of TiO2 nanoparticles larger than the threshold value 10−2 wt. %. The four lines were attributed to non-controlled impurity As substituted for P. In the presence of TiO2 nanoparticles, non-paramagnetic AsO43− clusters trap electrons becoming AsO44−. Disappearance of Fe3+ and Cr3+ centers was explained by their recharge to “EPR-silent” states and/or pairing at the surface of TiO2 nanoparticles.