K. K. Maurya

Enhancement of second harmonic generation, optical and dielectric properties in l-asparagine monohydrate single crystals due to an improvement in crystalline perfection by annealing

Single crystals of the relatively new nonlinear optical material l-asparagine monohydrate have been successfully grown by the slow evaporation solution growth technique at room temperature in aqueous solution. The crystal system nof the title material has been confirmed by powder X-ray diffraction. The crystalline perfection of the as-grown and annealed crystals has been evaluated by high-resolution X-ray diffraction. The as-grown single crystals (particularly when their size is large) were found to contain internal structural grain boundaries, and the crystalline perfection of these crystals was found to be nimproved substantially by annealing at low temperatures. The crystalline perfection and the measured physical properties were found to be correlated such that the second harmonic generation efficiency, optical transparency, nfluorescence and dielectric properties are enhanced as the crystal quality improves.

Effect of necking on Czochralski-grown LiF crystals and its influence on crystalline perfection and the correlated physical properties

A bulk single crystal of lithium fluoride (LiF) was grown using an in-house-developed Czochralski crystal puller. The effect of necking on crystalline perfection, which in turn was found to influence the optical and dielectric properties, was studied. The crystalline perfection of the grown crystal was assessed along the length of the boule using high-resolution X-ray diffraction (HRXRD), and it was found that the grain boundaries that were present in the seed crystal were stopped gradually from propagating into the bulk crystal by necking. The UV–vis transparency of the crystal region having best crystalline perfection was found to be higher. Photoluminescence (PL) spectra revealed that a crystal region that was found to contain vacancy (point) defects by HRXRD yielded the maximum PL intensity because of color centers at the vacancies. The dielectric properties were also studied over a wide range of frequency.

Remarkable enhancement in crystalline perfection, second harmonic generation efficiency, optical transparency, and laser damage threshold in potassium dihydrogen phosphate crystals by L-threonine doping

Effect of L-threonine (LT) doping on crystalline perfection, second harmonic generation (SHG) efficiency, optical transparency, and laser damage threshold (LDT) in potassium dihydrogen phosphate (KDP) crystals grown by slow evaporation solution technique (SEST) has been investigated. The influence of doping on growth rate and morphology of the grown crystals has also been studied. Powder x-ray diffraction data confirms the crystal structure of KDP and shows a systematic variation in intensity of diffraction peaks in correlation with morphology due to varying LT concentration. No extra phase formation was observed which is further confirmed by Fourier transform Raman (FT-Raman) studies. High-resolution x-ray diffraction curves indicate that crystalline perfection has been improved to a great extent at low concentrations with a maximum perfection at 1 molu2009% doping. At higher concentrations (5 to 10 molu2009%), it is slightly reduced due to excess incorporation of dopants at the interstitial sites of the crystal...

The effect of Cr3+ doping on the crystalline perfection and optical properties of zinc tris(thiourea)sulfate, a nonlinear optical material

A study of the effect of Cr3+ doping in zinc tris(thiourea)sulfate (ZTS, a well known nonlinear optical material) single crystals on crystalline perfection and optical properties was carried out. Pure and chromium-doped (1 and 2 mol%) ZTS single crystals were grown by the slow evaporation solution technique. The actual concentration of chromium incorporated into the crystal lattice was found to be different, as evaluated by flame atomic absorption spectroscopy. High-resolution X-ray diffraction (HRXRD) analysis revealed that chromium doping led to the creation of vacancies in the grown single crystals. The photolumin-escence emission spectra of pure and doped crystals supported the HRXRD findings. The optical band gap of the single crystals increased as a result of the Cr3+ doping, but their transparency in the visible region decreased. The doped crystals exhibited higher linear refractive indices than the pure crystals. The optical dielectric constant (), the extinction coefficient (k), the average single- noscillator energy for electronic transitions (Eo) and the oscillator strength (Ed) were evaluated for ZTS single crystals and significant changes were observed in these parameters due to the Cr3+ doping.

Crystalline perfection, Raman, UV-VIS-NIR and prism coupler investigations on Cz-grown pure and Zn-doped LiNbO3 single crystals

Pure and Zn-doped (1 mol%) LiNbO3 single crystals have been grown by the Czochralski technique. From powder X-ray diffraction analysis, the crystal structure and the lattice strains have been evaluated. The crystalline perfection analysis by high resolution X-ray diffraction revealed that the pure crystal is free from structural grain boundaries and contains predominantly vacancy defects whereas the doped crystal contains low angle structural grain boundaries. The Raman spectral studies indicate no variation in lattice vibrations with slight changes in the peak width and intensity. The Zn doping in crystals leads to an enhancement in optical transparency over the entire visible and near-infrared wavelength range and optical band gap. The prism coupler, refractive indices and birefringence measurements infer that the doped crystal is suitable for photorefractive applications in the ultraviolet wavelength region. The evaluated Li concentration by Raman and UV, as well as birefringence depicts that the grown crystals are congruent in nature with a slight deviation from stoichiometry.

Unidirectional growth of L-cysteine hydrochloride monohydrate: first time observation as nonlinear optical material and its characterization

A bulk size (∼60u2005mm length and 20u2005mm diameter) single crystal of l-cysteine hydrochloride monohydrate has been successfully grown for the first time by the unidirectional Sankaranarayanan–Ramasamy method and found to be a nonlinear optical material by observing the second harmonic generation (SHG). The crystal structure has been confirmed by single-crystal as well as powder X-ray diffraction analysis. The Fourier transform–Raman technique was used to study the vibrational modes and functional groups. The grown crystal was found to be highly transparent. The crystalline perfection has been evaluated by high-resolution X-ray diffractometry and the grown crystal was found to be free from macroscopic defects such as structural grain boundaries. The relative SHG efficiency and laser damage threshold values were found to be 1.2 and 5.5 times that of a potassium dihydrogen phosphate crystal, respectively. The dielectric constant, dielectric loss and alternating current conductivity were measured by an impedance analyser over a wide range of frequency between 100u2005Hz and 5u2005MHz. The dielectric constant was found to be stable for the entire range of frequency with very small dielectric loss, making this material suitable for device applications. The present investigation reveals that the title compound, since it can be grown with desirable size along a predetermined direction and it is a good nonlinear optical material with the prerequisite optical and dielectric properties, is a good candidate for photonic or opto-electronic applications.

Unidirectional crystal growth and crystalline perfection of l-arginine phosphate monohydrate

A large (∼20u2005mm diameter and 80u2005mm length) single crystal of l-arginine phosphate monohydrate (LAP) has been grown for the first time by the unidirectional Sankaranarayanan–Ramasamy method in an aqueous medium in a specially designed constant-temperature bath. The crystal structure has been confirmed by powder X-ray diffraction. The crystalline perfection was assessed by high-resolution X-ray diffractometry (HRXRD) which found that the quality of the grown single crystal is quite good. HRXRD studies along different directions show that the crystal contains a low density of edge-type dislocations formed along the growth direction. The thermal stability was assessed using thermogravimetric/differential thermal analysis. The mechanical behaviour was studied using an Omnitech micro-hardness tester. The dielectric studies were carried out over a wide frequency range of 10u2005Hz to 5u2005MHz at room temperature. The characterization studies reveal that the grown bulk single crystal of LAP is suitable for device applications.

Effect of ampoule support on the growth of organic benzimidazole single crystals by vertical Bridgman technique for nonlinear optical applications

Benzimidazole single crystals were grown using a vertical Bridgman technique with modified ampoule design. The thermal fluctuations during the melt were effectively controlled by the glass ampoule support which was filled with alumina wool in order to maintain a proper temperature gradient throughout the growth process. The unit cell dimensions of the grown crystals were assessed using powder X-ray diffraction technique. Comparative analyses have been carried out for both the crystals which were grown using a conventional ampoule and using the ampoule with support, via high resolution X-ray diffraction and it was found that there was a significant enhancement in crystalline perfection for the crystal which was grown using the ampoule with support. Further, optical transmission and photoluminescence studies on the grown crystals were carried out using UV-vis and photoluminescence spectroscopy and it was observed that there was a noticeable variation in the optical transmission and luminescence results.

Influence of polar solvents on growth of potentially NLO active organic single crystals of N-benzyl-2-methyl-4-nitroaniline and their efficiency in terahertz generation

We report on the growth of N-benzyl-2-methyl-4-nitroaniline (BNA) crystals by a solution growth method using certain polar protic and aprotic solvents (single or mixed). It was observed that the morphology of the BNA crystals could be influenced by the solvents used and that the growth was, with certain exceptions, predominant along the crystallographic b axis. Attempts to grow large BNA crystals from these solvents showed that the majority of these polar solvent molecules tended to get adsorbed preferentially along the polar +c and/or −c axes/axis. The bulk and surface qualities of the grown crystals were observed to be influenced by the solvents employed to grow the BNA crystals and the results of THz measurements obtained for the crystals grown from selected solvents were also found to corroborate these observations. A systematic approach has shown that the BNA crystals grown from one of the polar aprotic solvents, which is presumably reported for the first time for this crystal, exhibited a relatively higher THz efficiency. It is further understood that this particular solvent created a favorable solute–solvent environment at the progressing crystal–solution interface which improved the overall quality of the BNA single crystals and resulted in the significant enhancement in the THz efficiencies.

An in-depth study into the growth aspects and characteristic properties of ethyl 4-amino benzoate: a potential candidate for electro-optical applications

In the present work we report the growth of a bulk size ethyl 4-amino benzoate crystal, a potential candidate for electro-optical applications, using an indigenously developed single zone transparent resistive furnace because of observed difficulties involved in its growth via a solution growth technique. The structure of the grown crystal was examined using single crystal X-ray diffraction and it was found that it crystallized in an orthorhombic crystal system with the non-centrosymmetric space group P212121. The lattice parameters of the title material were further analysed using powder X-ray diffraction and they were found to be in agreement with the single crystal X-ray diffraction results. The strain in the lattice of the grown crystal was evaluated using the Hall–Williamson relation. The quality of the grown crystal was examined using a high resolution X-ray diffraction technique. Surface defects on the grown crystal were analysed using an etching technique. The transparency of the grown crystal was assessed using UV-vis spectroscopy and it was observed that the crystal possesses reasonably good transmittance over the visible spectrum. The optical band gap was also evaluated using Taucs plot. Furthermore, the laser damage threshold value was calculated using a Nd:YAG laser. Moreover, the thermal parameters and mechanical properties of the grown crystal were evaluated using photopyroelectric and nano-indentation techniques and it was observed that the crystal possesses quite fair thermal stability, however, the mechanical strength was low. With reduction in defects as observed it could be a potential candidate for non-linear optical applications.