Growth and characterization of l-phenylalanine nitric acid, a new organic nonlinear optical material

A new organic nonlinear optical material L-phenylalanine nitric acid [2C₉H₁₁NO₂.H⁺. NO₃⁻] (LPN), was synthesized in mixed solvent of deionised water and methanol and single crystals of LPN was grown by slow evaporation method. Transparent crystals upto 2.9 × 0.3 × 0.05 cm³ were obtained. The grown crystals have been subjected to powder X-ray diffraction studies to identify the crystalline nature. Single crystal X-ray diffractometer was utilized to measure unit cell parameters and to confirm the crystal structure. The modes of vibration of different molecular groups present in LPN were identified by FTIR spectral analysis. Transmission spectra reveals that the crystal has low UV cutoff of 295 nm and has a good transmittance in the entire visible region enabling its use in optical applications. Thermal properties of the crystals have been investigated using thermogravimetric (TG) and differential thermal analyses (DTA), which indicate that the material does not decompose before melting. The existence of second harmonic generation signals was observed using Nd:YAG laser with fundamental wavelength of 1064 nm.     

Synthesis and characterization of pure,urea and thiourea doped organic NLO l-arginine trifluoroacetate single crystals

Optically transparent l-arginine trifluoroacetate (LATF) single crystals by doping with organic materials urea and thiourea were grown by slow solvent evaporation technique. Powder X-ray diffraction confirms improvement in the crystalline quality for urea doped crystals. Urea doping in LATF also improves the percentage of transmittance. The vibrational frequencies of the grown crystals were assigned by Fourier Transform infrared spectroscopy. The thermal analysis (TG/DTA) indicated the better thermal stability for urea doped LATF crystals. EDAX analysis was carried out to calculate the percentage of elements present in doped and pure LATF. The hardness has been remarkably improved on urea and thiourea doped LATF crystals. The second harmonic generation (SHG) analysis showed 2.5 times than standard KDP for pure LATF and 2.2, 2.07 times than KDP for urea and thiourea doped LATF.     

Crystallization and characterization of nonlinear optical material l-arginine formomaleate

The influence of mixed acids in the growth and characteristic properties of a new nonlinear optical material l-arginine formomaleate abbreviated as LAFM was examined. Single crystal X-ray diffraction analysis was used to calculate the lattice parameters of the crystals. Fourier transform infrared (FTIR) spectroscopy and thermal analysis (DTA, TGA) were performed to study the molecular vibrations and thermal behaviour of the crystals. UV-VIS spectral study shows that LAFM is transparent down to 315 nm and its second harmonic generation efficiency is 1.2 times that of KDP.     

Theoretical investigations of optical properties of l-arginine trifluoroacetate crystal

In order to determine the molecular dipole moment (μ), polarizability (α), and first hyperpolarizability (β) of l-arginine trifluoroacetate (LATF) crystals, a series of basis sets including polarized and diffuse functions have been employed at the framework of Hartree–Fock and second order Möller–Plesset perturbation theory methods. The MP2/6-311++G(d,p) model predicts for the converged value of in-crystal dipole moment, polarizability and first hyperpolarizability are 21.2 D, 20.0 × 10⁻²⁴ esu and 50.0 × 10⁻³¹ esu, respectively. The calculated HOMO and LUMO energies show that charge transfer occur within the molecule. Electronic excitation properties are discussed within the framework of the two-level model on the basis of an orbital analysis. The coupled perturbed Hartree–Fock (CPHF) procedure yields information on the dispersion behavior of first hyperpolarizability terms. The magnitudes of the various hyperpolarizability terms which describe the various second-order nonlinear processes show the following trend: β(−2ω;ω,ω) > β(0;ω,−ω) > β(0,0,0). By using the molecular structures and the molecular first hyperpolarizability, the components of second harmonic tensor coefficient d of the crystals were evaluated by the oriented-gas model.     

Photoacoustic investigations on thermal anisotropy in urea l-malic acid single crystals

Laser-induced photoacoustic technique in the closed cell configuration has been employed to study the anisotropy in thermal parameters of urea l-malic acid, a nonlinear optical crystal. Thermal diffusivity values of the specimen along different crystallographic axes are evaluated from the measured amplitude and phase spectra of photoacoustic signal using one-dimensional model of Rosencwaig and Gersho. Thermal conductivity of the crystal along different axes is calculated using the measured thermal diffusivity and specific heat values. The measured thermal parameters are correlated with mechanical hardness as well as the bonding scheme of the crystal. Analyses of the results show that there is considerable anisotropy in heat diffusion parameters along different crystal orientations. Results are explained on the basis of crystallographic structure and the phonon-assisted heat diffusion mechanism in crystals.     

Electrical characterization on l-tyrosine doped triglycine sulfate single crystals

Dielectric, hysteresis, and scanning electron microscope studies on l-tyrosine doped triglycine sulfate (TyTGS) are reported. Increase in the relative permittivity compared to triglycine sulfate is observed on the doped crystal. Low frequency dielectric relaxation process is found to be modified in TyTGS crystals. No significant change in the spontaneous polarization compared to pure triglycine sulfate is observed. Increase in the coercive field in TyTGS compared to pure triglycine sulfate suggests that the dopant hinders the domain wall motion. Lens shaped domains, typical of triglycine sulfate are also observed on TyTGS crystal.     

Studies on lithium l-ascorbate dihydrate: An interesting chiral nonlinear optical crystal

Lithium l-Ascorbate dihydrate (LLA) is a new metal organic nonlinear optical crystal belonging to the saccharide family. Single crystals of LLA were grown from aqueous solution. Solubility of the crystal has a positive temperature coefficient facilitating growth by slow cooling. Rietveld refinement was used to confirm the phase formation. The crystal has prismatic habit with (010), (001) and (10−1) prominent faces. Thermal analysis shows that the crystal is stable up to 102 °C. Transmission spectrum of the crystal extends from 302 nm to 1600 nm. Dielectric spectroscopic analysis revealed Cole–Cole behaviour and prominent piezoelectric resonance peaks were observed in the range of 100–200 kHz. Second harmonic generation (SHG) conversion efficiency of up to 2.56 times that of a phase matched KDP crystal was achieved when the (010) plate of LLA single crystal was rotated about the +ve c axis, by 9.4° in the clockwise direction. We also observed SHG conical sections which were attributed to noncollinear phase matching. The observation of the third conical section suggests very high birefringence and large nonlinear coefficients. A detailed study of surface laser damage showed that the crystal has high multiple damage thresholds of 9.7 GW cm⁻² and 4.2 GW cm⁻² at 1064 nm and 532 nm radiation respectively.     

Investigation on structural,optical, thermal,mechanical and dielectric properties of l-proline cadmium chloride monohydrate single crystals: An efficient NLO material

In the present work, we have grown single crystals of l-proline cadmium chloride monohydrate (LPCCM) by slow evaporation solution technique (SEST) at room temperature and recorded their live growth kinetics with the help of inverted microscope. Crystal size at various stages of growth and its corresponding morphology was also recorded. Powder X-ray diffraction (PXRD) analysis of LPCCM single crystals confirmed the orthorhombic structure. Respective values of crystallite size, strain and dislocation density have been calculated using PXRD data. Metal complex coordination of the single crystal is studied by FTIR spectroscopic. The optical properties of the grown crystals were investigated through UV–VIS spectroscopic studies and shows that the crystals have very low absorption in entire characterized wavelength range 200–800 nm. The optical band gap was calculated and found to be ∼5.6 eV. Optical constants of the material is determined by theoretical calculations. The chemical etching study was also carried out to study the density of defects in the grown crystals. The photoluminous excitation and emission spectra and thermal property by TGA/DTA curve were recorded. Further, the mechanical properties have been studied using Vicker's microhardness tester as well as many parameters such as fracture toughness (K_c), Brittleness index (B_i) and yield strength (σ_ν) are presented. Dielectric studies have been carried out with varying frequency and temperatures.     

Growth and characterization of dl-Alanine — A new NLO material from the amino acid family

Single crystals of dl-Alanine (C₃H₇NO₂), one among the rare amino acid racemates crystallizing in a non-centrosymmetric space group and a new NLO material, were grown from aqueous solution by slow evaporation method. They were characterized by single crystal X-ray diffraction. Fourier transform infrared spectroscopy (FTIR) showed the presence of the different functional groups. The thermal stability and decomposition of the sample was studied by thermal analysis (TGA/DTA). The optical transparency was studied by UV–Vis–NIR spectral analysis. The above experimental results showed that dl-Alanine is stable up to 280 °C and transparent in the region of 220 nm–1100 nm. The second harmonic generation (SHG) efficiency was determined using Kurtz and Perry method and found to be 1.7 times higher than that of standard KDP.     

Study of pure and l-tartaric acid doped ammonium dihydrogen phosphate single crystals: A novel nonlinear optical non-centrosymmetric crystal

Single crystals of pure and l-tartaric acid (LTA) C₄H₆O₆ doped ammonium dihydrogen phosphate (ADP) (NH₄) H₂PO₄ were grown by slow evaporation solution technique (SEST) at ambient conditions. Powder X-ray diffraction (PXRD) analysis was carried out to confirm the crystal structure and no additional phase was observed due to doping except a systematic variation in peak intensities. Fourier transform infrared spectral analysis was done to examine the presence of various functional groups in the grown crystals. UV–VIS–NIR spectroscopic analysis was carried out to see the change in optical transparency of pure ADP and crystals due to LTA with different doping concentrations. Second harmonic generation (SHG) efficiency measurement was done to examine the enhancement in the nonlinear optical characteristics of the grown crystals. The effect of LTA dopant on crystal morphology, thermal and mechanical properties of ADP have also been presented in this paper. The above studies reveal the effect of incorporation of LTA into the lattice of ADP crystals.     

Effect of l-alanine,Mn(II) and glycine dopants on the structural,crystalline perfection,second harmonic generation (SHG), dielectric and mechanical properties of BTCA single crystals

Bis thiourea cadmium acetate (BTCA) single crystals were grown at room temperature with different dopants by aqueous solution technique. The crystal system of the grown crystals with all the dopants was confirmed by powder X-ray diffraction study which confirms that there is no extra phase due to doping of l-alanine (LA), Mn(II) and glycine (Gly). It was further confirmed by FT-IR as well as FT–Raman spectroscopy analysis. The effect of LA, Mn(II) and Gly doping on the crystalline perfection was assessed by high-resolution X-ray diffractometry (HRXRD) analysis which revealed that the grown crystals with Gly doping are more perfect in comparison of other dopants. The SHG efficiency was measured using the Kurtz powder technique and shows that the grown crystals with Gly doping are more efficient in comparison of other dopants which is in tune with crystalline perfection. The low values of dielectric constant and loss also revealed that the grown crystals are defect free. The hardness values were found to be increased by increasing the doping concentration.     

Optical,mechanical and transport properties of unidirectional grown l-tartaric acid bulk single crystal for non-linear optical application

Good optical quality bulk single crystal of l-tartaric acid has been grown by directional solidification crystal growth method from aqueous solution. Crystal of dimension 77 mm length and 12 mm diameter has been grown at a growth rate of 2.5 mm day⁻¹ which is the maximum size and growth rate achieved so far. The grown crystal was confirmed by powder XRD analysis and the presence of the functional groups in the crystal lattice was confirmed by Fourier transform infrared spectral analysis. Transmission spectral analysis shows that the crystal has more than 90% of transmittance in visible and near infrared region which exhibits the good optical quality of the crystal. The optical band gap was estimated to be 4.8 eV and it shows indirect optical transition. Thermal analysis shows the crystal to be thermally stable up to 172 °C and the load variation of the hardness has been explained on the basis of normal indentation size effect from microhardness study.     

Growth and characterization of an organic nonlinear optical material: l-alanine alaninium nitrate

l-alanine alaninium nitrate (LAAN), an organic nonlinear optical material was grown by slow evaporation technique at room temperature from its aqueous solution at pH value of 2.5. As grown single crystals were characterized for its spectral, thermal, linear and second order nonlinear optical properties. LAAN crystallizes in monoclinic system with space group P₂₁ and cell parameters a = 7.846 Å, b = 5.431 Å, c = 12.806 Å and β = 94.65°. The mode of vibrations of different molecular groups present in LAAN were identified by FTIR studies. The thermal behaviour of the crystals has been investigated using thermogravimetry (TG) and differential thermal analysis (DTA), which indicates that the material does not decompose before melting. Transmittance spectrum reveals that the crystal has a low UV cut-off of 320 nm and has a good transmittance in the entire visible region. NLO property of the crystal was confirmed by Kurtz SHG powder technique.     

Characterization of vapor-deposited l-leucine nanofilm

X-ray reflective measurements (XRR), atomic force microscopy and single wavelength ellipsometry were used to investigate the optical properties of thin l-leucine films deposited onto silicon substrates. The ellipsometry data (Ψ,Δ) were fitted with a four-layer-model, and the optical refractive index of the l-leucine film measured with ellipsometry was determined to be 1.37. With the conventional effective medium approximation theory and the ellipsometry results, the density of the l-leucine nanofilm was determined to be 70% (0.81 g/cm³) of crystalline l-leucine. This value was in good agreement with the density of 69% (0.80 g/cm³) obtained with XRR measurement. The ellipsometry measurements also enabled us to estimate the surface roughness or absorption layer of the film. This procedure of combined XRR and ellipsometry measurements could be a powerful tool for the determination of the (otherwise hard-to-determine) refractive index in thin organic material films with a rough surface layer.     

Crystal growth and spectral properties of Pr:La2(WO4)3

Pr³⁺-doped La₂(WO₄)₃ single crystal with dimensions up to Ø 20 mm × 35 mm has been grown by the Czochralski method. The structure of the Pr³⁺:La₂(WO₄)₃ crystal was determined by the X-ray powder diffraction and the Pr³⁺ concentration in this crystal was determined. The absorption and fluorescence spectra of Pr³⁺:La₂(WO₄)₃ crystal were measured at room temperature, and the fluorescence lifetime of main emission multiplets were estimated from the recorded decay curves. The spectral properties related to laser performance of the crystal were evaluated.     

Interfacial bonding of Flax fibre/Poly(l-lactide) bio-composites

The use of glass fibre reinforced polyester composites raises many health and safety and environmental questions. One alternative is the development of high performance bio-based bio-composites with low environmental impact. Improved understanding of interfacial properties is essential to optimise the mechanical properties and durability of these materials, but so far few data are available. The present work describes the interfacial characterization of Flax fibre/Poly(lactic) acid (PLLA) system at the micro-scale using the microbond test. Different thermal treatments have been carried out (cooling rate and annealing) in order to evaluate the influence of matrix and interfacial morphologies as well as residual stress on interfacial properties. Micromechanical models have been used to determine the interfacial shear strength. When cooling rate is slow, improved interfacial properties are observed.     

Synthesis, growth, and characterization of nonlinear optical material l-arginine iodate crystal

Single crystals of nonlinear optical l-arginine iodate (l-Arg·2HIO₃) (C₆H₁₄N₄O₂·2HIO₃), were successfully grown for the first time by the temperature-lowering method and also by the slow evaporation method at a constant temperature (30 °C) from its aqueous solution at pH value of 6. Crystals were of average dimensions 3 × 2.5 × 1.0 cm³ by optimizing the growth parameters. Initially, solubility studies were carried out for four different solvents such as water, water-methanol, water-ethanol, and water-acetone. Among the four solvents, the solubility of l-Arg·2HIO₃ was found to be the highest in water and hence crystallization of l-Arg·2HIO₃ was carried out from aqueous solution. Morphology studies reveal that the crystals grow with reasonable growth rate along the [100], [001], [110¯] and [011] direction. As-grown crystals were characterized by density measurement, X-ray powder diffraction studies, infrared spectrophotometer, UV-Vis spectrometer, laser induced damage threshold studies and nonlinear optical study.     

Thermal, dielectric studies on pure and amino acid (l-glutamic acid, l-histidine, l-valine) doped KDP single crystals

Amino acids (l-glutamic acid, l-histidine, l-valine) doped potassium dihydrogen phospate crystals are grown by solution growth technique. Slow cooling as well as slow evaporation methods were employed to grow these crystals. The concentration of dopants in the mother solution was varied from 0.1 mol% to 10 mol%. The solubility data for all dopants concentration were determined. There is variation in pH value and hence, there is habit modification of the grown crystals were characterized with UV–VIS, FT-IR studies, SHG trace elements and dielectric studies reveal slight distortion of lattice parameter for the heavily doped KDP crystals. UV–Visible spectra confirm the improvement in the transparency of these crystals on doping metal ions. FT-IR spectra reveal strong absorption band between 1400 and 1600 cm⁻¹ for metal ion doped crystals. TGA–DTA studies reveal good thermal stability. The dopants increase the hardness value of the material and it also depends on the concentration of the dopants. Amino acids doping improved the NLO properties. The detailed results on the spectral parameters, habit modifications and constant values will be presented.     

Growth, characterization and optical quality of CaF2 single crystals grown by the temperature gradient technique

The CaF₂ single crystals with diameters up to 200 mm were successfully grown by modified temperature gradient technique (TGT), which are suitable for application as optical elements in the ultraviolet range. The optimizations of various growth parameters were systematically studied. Properties of as-grown CaF₂ crystals were characterized by the nature of inclusions, dislocations, crystallinity, and impurities contents. The results showed that the dislocations and multinucleation were mostly constrained in the conical part of the crystals with the cylindrical parts having the best crystalline quality and lowest impurity contents. The high optical quality of TGT-grown CaF₂ single crystals was also confirmed to have excellent optical transmission in 190-2500 nm and refractive index homogeneity.     

Synthesis and characterization of biodegradable poly(l-lactide)/layered double hydroxide nanocomposites

This study reports the preparation and physical properties of biodegradable nanocomposites fabricated using poly(l-lactide) (PLLA) and magnesium/aluminum layered double hydroxide (MgAl-LDH). The MgAl-LDH with molar ratio of Mg/Al = 2 were synthesized by the co-precipitation method. In order to improve the chemical compatibility between PLLA and LDH, the surface of LDH was organically-modified by polylactide with carboxyl end group (PLA–COOH) using ion-exchange process. Then, the PLLA/LDH nanocomposites were prepared by solution intercalation of PLLA into the galleries of PLA–COOH modified LDH (P-LDH) in tetrahydrofuran solution. Both X-ray diffraction data and Transmission electron microscopy images of PLLA/P-LDH nanocomposites indicate that the P-LDHs are randomly dispersed and exfoliated into the PLLA matrix. Mechanical properties of the fabricated 1.2 wt.% PLLA/P-LDH nanocomposites show significant enhancements in the storage modulus when compared to that of neat PLLA. Adding more P-LDH into PLLA matrix induced a decrease in the storage modulus of PLLA/P-LDH nanocomposites, probably due to the excessive content of PLA–COOH moleculars with low mechanical properties. The thermal stability and degradation activation energies of the PLLA and PLLA/P-LDH nanocomposites can also be discussed.