Crystalline perfection and optical properties of rapid grown KH2PO4 crystal with chromate additive

Potassium dihydrogen phosphate (KDP) crystals were grown in the presence of a series of chromate (CrO) additive concentrations via rapid growth method. CrO made KDP crystals were coloured by yellow-green, suggesting CrO had entered into the crystal lattice. The elemental analysis indicated that Cr element in KDP crystal was at ppm level. High resolution X-ray diffraction data revealed that the crystalline perfection of these as-grown KDP crystals was destroyed after CrO entered into crystal lattice, embedded in the full width at half maximum was broadened and satellite peaks appeared. Additionally, the extinction ratio was decreased with rise of CrO concentration. CrO introduced two absorption peaks centred at 360 and 280 nm and enhanced the intrinsic absorption near 220 nm, which were at the same band positions compared with the CrO or HCrO transmittance spectra. Additionally, CrO could increase the size of light scattering, which was attributed to the point defects and microscopic defects by the replacement by CrO at PO position.