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 $_{4}^{2-}$ ) additive concentrations via rapid growth method. CrO $_{4}^{2-}$ made KDP crystals were coloured by yellow-green, suggesting CrO $_{4}^{2-}$ 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 $_{4}^{2-}$ 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 $_{4}^{2-}$ concentration. CrO $_{4}^{2-}$ 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 $_{4}^{2-}$ or HCrO $_{4}^{-}$ transmittance spectra. Additionally, CrO $_{4}^{2-}$ could increase the size of light scattering, which was attributed to the point defects and microscopic defects by the replacement by CrO $_{4}^{2-}$ at PO $_{4}^{3-}$ position.