K. Ramachandra Rao

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.

Studies on influence of Cd2+ ions in unidirectional growth and characterization of l-Cysteine hydrochloride monohydrate single crystals

Cadmium doped l-Cysteine hydrochloride monohydrate (Cd(2+)-C3H7NO2S⋅HCl⋅H2O), a non-linear optical crystal, was grown by conventional as well as unidirectional solution growth techniques. While the dimension of the conventionally grown crystal was 16×14×5mm(3), the dimension of the crystal grown unidirectional method was 32mm long and 6mm diameter. The grown crystals were studied using XRD for phase analysis, HRXRD for crystalline perfection and UV-Vis NIR spectroscopy for optical properties. The high crystalline perfection was found in the crystal grown by unidirectional method than that grown by conventional one. FTIR study indicates that Cd(2+) ion was coordinated to l-Cysteine⋅HCl⋅H2O through S ligand. The nonlinear optical character of the title compound was observed by measuring the SHG efficiency, which is 1.35times to that of KDP by Kurtz technique.

Structural and optical properties of Cd2+ ion on the growth of sulphamic acid single crystals

Transparent single crystals of Cadmium doped Sulphamic acid (SA) was grown by Conventional slow evaporation solution technique (SEST) which had the size of 13 × 8 × 7 mm3. The grown single crystals have been characterized using single crystal X-ray diffraction UV-visible Spectral studies and Second harmonic generation (SHG) efficiency and the results were discussed. The lattice parameters of the grown Cd2+ ion doped SA crystal are confirmed by single crystal X-ray diffraction and belong to orthorhombic system. Optical transmittance of the crystal was recorded using UV-vis NIR spectrophotometer with its lower cut off wavelength around 259nm. SHG measurements indicate that the SHG efficiency of the grown Cd2+ ion doped SA crystal at a fundamental wavelength of 1064 nm is approximately equal to KDP.

Luminescence from ZnS: Bulk Vs Nano

Based on the detailed luminescence studies on bulk and nanoparticles of ZnS, it is inferred that the defect emission due to zinc (VZn) and sulfur (VS) vacancies in ZnS, significantly change in terms of line shape and peak position, when bulk form is converted to nanoparticles. From the XRD studies, this has been explained in terms of difference in the crystalline modifications of ZnS, namely the wurtzite and cubic forms. Copper doping in the sample quenches the luminescence and stabilize the cubic phase. Bright blue electro luminescence (efficiency of around 1.5 %) with CIE coordinates (0.18. 0.11) could be seen from bulk ZnS:Cu sample. Unlike this the nanoparticles did not give any emission due to the quenching of charge carriers/excitons. Lifetime values further supported these inferences.

The Influence Of Zn2+ on Growth and Characterization of L–Cysteine Hydrochloride Monohydrate Nlo Single Crystals

The influence of transition metal Zn2+ on the L-Cysteine Hydrochloride monohydrate (L-Cys.HCl.H2O), a non- linear optical single crystal hasbeen studied through XRD, HRXRD, FT-IR, UV-Vis and SHG. A close observation of FT-IR and HRXRD profiles of doped and undoped samples showed some minor structural variations.FT-IR spectra also reveal that S-H and C-S functional groups are involved in Zn coordination through S-ligand in L-Cys.HCl.H2O. A HRXRD and UV-Vis study infers the good crystalline perfection and high optical transparency. The nonlinear optical efficiency estimation was done by Kurtz technique of grown crystal, which was 1.3 times that of standard KDP.