Incorporation of Cr-containing anionic species into potassium dihydrogen phosphate crystal

Abstract

By altering the concentration of chromate (CrO42−) additive in the growth solution, a series of potassium dihydrogen phosphate (KDP) crystals was obtained by the conventional temperature cooling method. The addition of CrO42− resulted in yellow-green colored KDP crystals. The measurement of the growth rate revealed that CrO42− made a small contribution to the growth rate of (100) face. The configurations of CrO42− in a saturated KDP solution were confirmed to be Cr2O72− and HCrO4−. Through electrostatic attractive force and charge-assisted hydrogen bonds, Cr2O72− and HCrO4− were selectively adsorbed onto (101) and (100) faces, respectively. The adsorbed Cr2O72− on the (101) face could be decomposed to CrO42− or HCrO4− because of the lower pH value in the growth boundary. CrO42− and HCrO4− could enter into crystal lattice because of the structural similarities of CrO42−–PO43−, and consequently made KDP crystals colored and resulted in transmittance adsorptions at 280 and 370nm in doped KDP crystals. Elemental analysis indicated that the concentration of Cr in KDP crystals increased with increasing CrO42− in the growth solution. Additionally, the influence of CrO42− on the growth of KDP crystals was similar to that of Cr2O72−.