Unidirectional growth of large size urea doped L-cysteine hydrochloride monohydrate NLO organic crystal and investigations of its crystalline and optical properties.

Organic crystals of urea doped L-cysteine hydrochloride monohydrate have been grown by unidirectional solution growth technique. The crystal grown by this technique has high growth rate as compared to the crystals grown using conventional slow cooling method. This method is ideally suited to grow crystals along a specific direction. The growth process was monitored at regular intervals of time in a time-lapsed manner to estimate the growth rate and also monitor its quality visually. The grown crystal was subjected to different characterizations in order to confirm the phase of the grown crystal, its crystalline perfection and optical properties. The X-ray diffraction confirmed the phase of the crystal. The rocking curve recorded using high resolution X-ray diffraction (HRXRD) technique reveals that the crystal grown using conventional slow cooling method has internal gain boundaries whereas that grown by unidirectional technique has high degree of crystalline perfection. The bonding environment present in the crystal was characterized by FTIR spectroscopy where vibrational frequencies of the different functional groups present were identified. The optical quality of the crystal was characterized using UV-vis-NIR spectrophotometer and Mach-Zehnder interferometer. The nonlinear optical response of the crystal was measured using Kurtz-Perry method and found to be 1.4 times that of a KDP crystal.

Synthesis of LiNbO3 Nanoparticles by Citrate Gel Method.

We present investigations on the preparation of nearly stoichiometric lithium niobate (LiNbO3) nanoparticles using citrate gel method. Citric acid is used as a chelating agent and ethylene glycol is added for polyestarification between the chelates. In addition to the main lithium niobate phase, the secondary phase of lithium niobate, LiNb3O8, and an unreacted phase of Nb2O5 were also observed in the resultant product. The appearance of unwanted phases is a serious problem in citrate gel method. We have observed that the synthesis parameters such as molar ratio of citric acid to metal ions (R1), pH, molar ratio of ethylene glycol to citric acid (R2) and calcination temperature strongly influence the presence of the unwanted phases and these parameters are optimized to remove these phases. Evolution of the phase was investigated by powder XRD whereas TG/DTA was done to find out the crystallization temperature. It was observed that nearly stoichiometric and pure LiNbO3 nanoparticles can be obtained with the optimized parameters, R1 = 3, pH = 8, R2 ≥ 2 and calcination temperature = 700 degrees C. The stoichiometry of the synthesized LiNbO3 nanoparticles was investigated using Raman spectroscopy.