Crystal. growth of Nd:RVO4 (where R = Y, Gd) under mild hydrothermal conditions

Full text: There is a growing interest in the study of Nd:RVO4(where R Y, Gd) compounds owing to their importance in laser applications in the recent years. Several methods like flux, melt and solid state synthesis have been adapted by many earlier workers to synthesise Nd:RVO4(where R = Y, Gd) compounds. However, there are only a scanty reports with regard to the hydrothermal growth of these crystals. This is probably connected with the high temperature and pressure conditions involved in the growth of these crystals. Further, these crystals are known to have high melting points and very low solubility. Therefore, the high temperature solution and melt techniques were preferred over the others. Here, the present authors report for the first time the growth of these crystals under mild hydrothermal conditions. The pressure was maintained at less than 100 bars and temperature was 240 deg C in all the experiments. The crystal growth experiments were carried out in standard Morey autoclaves. The starting materials such as Nd203. V205 and R203 were taken in a definite molar ratio in a teflon liner. In order to explore the possibility of obtaining these crystals under mild hydrothermal conditions, several mineralisers like NaOH, NaF, HCl HNO3, NH4Cl H2SO4 HCOOH, etc. with different concentrations were tried. Also the mixed mineralisers in different molar ratios were tried. It was found that high molar HCl is the suitable mineraliser to obtain these compounds under mild hydrothermal conditions. The hydrothermal chemistry of these compounds has been studied through the solvent-solute interaction, pH variation, and the appropriate hydrothermal reaction mechanism has been proposed to these crystals The crystallisation was carried out through spontaneous nucleation, and the experimental duration was 8 days. The crystals obtained were dark brown in colour, transparent, plate like in habit with square shape. The surfaces were quite smooth and vitreous. The size of the crystals varies from 1 to 2.3 mm. The crystals obtained were subjected to a systematic characterisation like morphological studies, X-ray diffraction, chemical analysis, thermal analysis, and infrared spectroscopy. Also the preliminary studied of the luminescent properties has been carried out