Study on rapid growth of KH2PO4 and its characterization

Large size crystals of KH₂PO₄ (KDP) were grown by adopting rapid growth technique from point seeds in a 1500‐liter crystallizer which is used to grow KDP crystals by conventional method. The grown KDP crystal size can reach to 310 × 310 × 320 mm³ and the average growth rate was 8mm/day. The optic properties of the rapidly grown KDP crystals were characterized comparing with the KDP crystals grown by the traditional temperature reduction method. We found it that the optical quality of the KDP crystals we grown rapidly are not significantly different from those of KDP crystals grown by traditional method. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of semi organic nonlinear optical LHPCL crystals

The growth of single crystals of L‐histidinium perchlorate (LHPCL), a semi organic nonlinear optical material with dimension upto 5 × 6 × 2.5 mm³ is reported. Good optical quality single crystals were grown from aqueous solution by slow solvent evaporation technique. The grown crystals were characterized by single crystal X‐ray diffraction (XRD), FT‐IR and optical transmission studies. Thermal studies confirm that LHPCL has a fairly high thermal stability (272°C) when compared with other members of histidine family. The scanning electron microscopy (SEM) provides information on the quality of the samples and grain distribution over the surface of the sample. The dielectric constant and dielectric loss of the compound were measured at different frequencies, and also at varying temperatures and the results of these experiments are discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The effect of cooling rate on size,quality and morphology of KTiOPO4 (KTP) crystals grown by different nucleation techniques

KTP crystals have been grown by two nucleation techniques namely spontaneous nucleation in flux medium and nucleation on Pt rod using K₆P₄O₁₃ flux.10 °C/h, 7 °C/h, 0.8 °C/h, 0.4 °C/h and 0.2 °C/h cooling rates were applied for spontaneous nucleation and crystals up to 15 × 7 × 4 mm³ in size were grown. 1 °C/h and 0.8 °C/h cooling rates were also used for nucleation on Pt rod and crystals up to 8 × 6 × 3 mm³ in size were grown. The effect of cooling rate on size, morphology and optical quality of grown crystals by both techniques were studied. For nucleation on Pt rod upper and lower rotation rates limits and an optimum rotation rate were distinguished for each cooling rate. Quality of the grown crystals by both techniques was characterized by optical transmission analysis.     

Structural,thermal and optical characterizations of a NLO material: L‐alaninium oxalate

An organic electro‐optic and nonlinear optical (NLO) material, L‐alaninium oxalate, was synthesized by the standard method. The synthesized material was purified by repeated recrystallization. Single crystals were grown by the slow evaporation technique. The grown crystals were transparent and had optimum dimensions (20 × 3 × 2 mm³) and were characterized by single crystal XRD, FT‐NMR, FT‐IR, TGA‐DTA and UV‐Vis‐NIR techniques. The second harmonic generation (SHG) from the material was confirmed using Nd:YAG laser. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Single crystal growth and properties of semiorganic nonlinear optical L‐arginine hydrochloride monohydrate crystals

L‐arginine hydrochloride monohydrate (LAHCl.H₂O) has been synthesized and single crystals have been grown from its aqueous solution by slow evaporation and slow cooling methods. The solubility of the material was measured at various temperatures and bulk crystals of size 26×13×11 mm³ have been grown by optimizing the growth parameters. The grown crystals have been subjected to single crystal XRD studies to confirm the structure and to estimate the lattice parameters. FTIR analysis indicate the mode of vibrations of different molecular groups present in LAHCl and confirm the protonation of guanidyl, amino groups and deprotonation of COO^‐ groups. UV‐Vis transmission spectrum revealed the linear optical properties of the grown crystals with a transparency of 65% over the entire visible range upto 300 nm. Thermal behavior of the grown crystal was investigated from DTA and TGA measurements. Dielectric studies have been carried out on the grown crystals. Kurtz and Perry powder SHG technique confirms the NLO property of the grown crystal. The SHG efficiency of LAHCl was found to be 0.38 with respect to KDP. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of YCOB single crystals by flux technique and their characterization

Nonlinear optical single crystals of YCOB with good optical quality were grown by the flux technique for the first time. Polycrystalline YCOB samples were synthesized by solid state reaction method. The thermal analysis of the sample was performed with lithium carbonate flux in different weight proportions and the growth temperature was optimised. Single crystals of YCOB with dimensions 3 × 3 × 5 mm³ were obtained by the method of ‘slow‐cooling’. The grown crystals were characterized by XRD, UV‐VIS‐NIR, EDAX, FTIR and etching studies. The powder XRD pattern revealed the formation of YCOB compound. The lattice parameters were identified through single crystal XRD studies. The UV‐VIS‐NIR results showed that the crystal has a sharp cutoff at 220 nm and is nearly 55% transparent over a wide wavelength range enabling applications in the UV region. The EDAX measurement revealed the ‘flux‐free’ crystal formation. The presence of the functional groups belonging to the YCOB crystals was identified by the FTIR results. ‘Hillock‐like’ patterns are observed in the etching studies. The primary emphasis in this study is laid to describe ‘flux technique’ as an alternative method to grow YCOB crystals. The results are presented and discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of bis-glycine sodium nitrate (BGSN), a novel semi-organic nonlinear optical crystal

Single crystals of bis-glycine sodium nitrate (BGSN), a semi-organic nonlinear optical (NLO) material, have been grown by slow cooling method. Good optical quality single crystals with dimensions up to 1.6×1.6×1.0 cm³ are obtained. Using a single-crystal diffractometer, the morphology of BGSN crystal was identified. Powder X-ray diffraction confirms the crystalline nature of BGSN. The grown crystals were characterized by optical transmission spectrum (UV) and FTIR studies. The NLO property of the crystal was confirmed by Kurtz second harmonic generation (SHG) test, and the output power generated by the crystal was compared with that of KDP. The thermal stability of the crystal was studied by thermo-gravimetric analysis (TGA), differential thermal analysis (DTA) and differential scanning calorimetry (DSC). Micro hardness study was carried out for different planes, and the anisotropy behavior of the crystal was observed.     

Growth and characterization of nonlinear optical zinc hydrogen phosphate single crystal grown in silica gel

Good optical quality single crystals of zinc hydrogen phosphate (ZnHPO₄) having dimensions up to 8×2×2 mm³ have been grown with the aid of sodium meta silicate gel. Single crystal XRD studies confirm that the crystal belongs to the orthorhombic system with space group P2₁2₁2₁. The functional groups present in the crystals were confirmed using FTIR technique. Optical absorbance shows very low absorption in the entire visible region. Differential thermal and thermo gravimetric analysis confirmed that the crystal is stable up to 193°C. Photoconductivity study reveals positive photoconductivity in the presence of photo active centers formed by trap energy levels. The NLO activity of the crystal was confirmed by Kurtz powder technique. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of α-NiSO<Subscript>4</Subscript> · 6H<Subscript>2</Subscript>O crystals at high rates

The high-rate growth of nickel sulfate hexahydrate NiSO₄ · 6H₂O (α-NSH) crystals up to 120 × 120 × 65 mm³ in size is described for the first time. The data on the distribution of related impurities in the {011} and {001} growth sectors of α-NSH crystals grown at different rates are reported. The transmission spectra of both growth sectors of these crystals are obtained. The structural quality and the optical properties of rapidly and slowly grown α-NSH crystals are compared. It is established that the {011} growth sector of crystals grown at rates exceeding 5 mm/day shows the best characteristics for application in UV filters.     

Growth and characterization of a novel NLO crystal bis-glycine hydrogen chloride (BGHC)

Single crystals of bis-glycine hydrogen chloride (BGHC), a semiorganic nonlinear optical (NLO) material, have been grown by slow solvent evaporation technique. Good optical quality single crystals with dimensions up to 33×5×5 mm³ are obtained. The crystals are characterized by optical transmission spectrum, FTIR and X-ray diffraction studies. The thermal stability of the crystal is studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The second harmonic generation (SHG) efficiency of BGHC was found to be 5.6 times that of KDP. The laser damage threshold values studied in single shot mode indicates that BGHC crystal possesses a fairly high value of 9.8 GW/cm² and thus the NLO studies confirmed the superiority of BGHC over KDP and urea crystals. The dielectric constant of the crystal was studied as a function of frequency and the results are discussed.     

Crystal growth,quality characterization and THz properties of DAST crystals

4‐N, N‐diethylamino‐4’‐N’‐methyl‐stilbazolium tosylate (DAST) crystals were grown by slope nucleation method (SNM). The crystal structure of grown DAST crystals was characterized by single crystal X‐ray diffraction with demonstrating X‐ray diffraction main peaks. The crystal defects were analyzed by the synchrotron radiation X‐ray topography. It was found that the unbalanced temperature gradient, the Teflon groove and the super saturation fluctuation were primary causes of crystal defects. Furthermore, widely tunable THz waves ranging from 1.16 to 16.71 THz were generated from 1 mm‐thick DAST crystal using the optical parametric oscillator (OPO). It was obtained that the THz output energy was 27.4 nJ (peak power of 2.74 W) and the highest conversion efficiency was 1.37 × 10⁻⁵ at 3.8 THz.     

Growth and characterization of L‐prolinium tartrate – A new organic NLO material

Single crystals of L‐Prolinium tartrate (C₅H₁₀NO₂)⁺ (C₄H₅O₆)^‐, a new organic non‐linear optical material of size: 15 × 10 × 10 mm³ were grown using submerged seed solution growth method. Characterization of the crystals was made using single crystal X‐ray diffraction and density determination. Spectroscopic, thermal, optical and mechanical studies were carried out. These studies show that the crystals are thermally stable upto 161°C, transparent for the fundamental and second harmonic generation of Nd: YAG (λ = 1064 nm) laser and possess good mechanical strength. Second harmonic generation (SHG) conversion efficiency was investigated to explore the NLO characteristics of this material using Kurtz and Perry method and it was found that the SHG conversion efficiency is about 90% of that of the standard KDP crystals. Laser damage threshold study was also carried out. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of a new langasite‐type single crystal Sr3NbAl1.5Ga1.5Si2O14

Single crystals of Sr₃NbAl_1.5Ga_1.5Si₂O₁₄ (SNAGS) with langasite structure have been successfully grown by Czochralski method. The X‐ray diffraction (XRD) verified that the as‐grown crystal was isostructural with A₃BC₃D₂O₁₄ structure and the lattice parameters were calculated as follows: a = 8.242 Å, c = 5.041 Å, V = 296.6 ų. The piezoelectric coefficient d₁₁ was 5.7pC/N, which was 2.47 times of α‐quartz (d₁₁=2.31pC/N). The electric resistivity was up to 3.04×10⁶ Ωcm at 700 °C for X‐cut sample. In addition, the transmission spectrum of the SNAGS crystal showed that it had a high transmittance (>80%) in the range of 350‐800 nm and exceeded 90% above 520 nm. These results suggest that the SNAGS crystals have potential applications in high‐temperature piezoelectric sensors and optical techniques. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Single crystal growth,structural, optical,mechanical, dielectric and thermal studies of formic acid doped potassium dihydrogen phosphate crystal for NLO applications

Optically transparent formic acid (FA) doped potassium dihydrogen phosphate (KDP) crystal of dimension 21×15×9 mm³ has been grown by slow evaporation solution technique (SEST). The X‐ray diffraction (XRD) technique was used to confirm the cell parameters and the shifts in peak positions of identified reflecting planes. The incorporation of FA in KDP has been qualitatively analyzed by fourier transform infrared analysis. The UV‐visible absorption spectrum of crystals has been recorded in the range of 200 to 900 nm and the doped KDP crystal is found to have improved optical parameters than pure KDP. The color centered photoluminescence emission spectrum of grown crystal has been illustrated in visible region. The mechanical behavior of pure and doped KDP crystal has been investigated using the Vicker's microhardness analyzer and hardness parameters have been calculated. The effect of FA on thermal stability of KDP crystal was examined by means of thermogravimetric and differential thermal analysis. The temperature dependent dielectric behavior of crystals was studied.     

Increased optical damage resistance of Zr:LiNbO3 crystals

Zr: LiNbO₃ crystals has been grown. The crystal composition and phase are analyzed by X‐ray diffration. The optical damage resistance ability of Zr: LiNbO₃ crystals is studied by the Sénarmont compensation method and the transmitted beam pattern distortion method. The saturated value of the birefringence change of 6 mol% Zr: LiNbO₃ crystal is 1.01×10^‐4, which is seven times smaller than that of congruent pure LiNbO₃ crystal. The results of UV‐Visible and IR absorption spectra of Zr: LiNbO₃ crystals powerfully confirm that the optical damage resistance threshold concentration of the Zr⁴⁺ ions doped in LiNbO₃ crystals is about 6 mol% in the melt. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Enhancement of thermoelectric efficiency in vapor deposited Sb2Te3 and Sb1.8In0.2Te3 crystals

Pure and indium doped antimony telluride (Sb₂Te₃) crystals find applications in high performance room temperature thermoelectric devices. Owing to the meagre physical properties exhibited on the cleavage faces of melt grown samples, an attempt was made to explore the thermoelectric parameters of p‐type crystals grown by the physical vapor deposition (PVD) method. The crystal structure of the grown platelets (9 mm× 8 mm× 2 mm) was identified as rhombohedral by x‐ray powder diffraction method. The energy dispersive analysis confirmed the elemental composition of the crystals. The electron microscopic and scanning probe image studies revealed that the crystals were grown by layer growth mechanism with low surface roughness. At room temperature (300 K), the values of Seebeck coefficient S (⊥ c) and power factor were observed to be higher for Sb_1.8In_0.2Te₃ crystals (155 μVK⁻¹, 2.669 × 10⁻³ W/mK²) than those of pure ones. Upon doping, the thermal conductivity κ (⊥ c) was decreased by 37.14% and thus thermoelectric efficiency was improved. The increased figure of merit, Z = 1.23 × 10⁻³ K⁻¹ for vapour grown Sb_1.8In_0.2Te₃ platelets indicates that it could be used as a potential thermoelectric candidate.     

Thermal and infrared studies of calcium malate crystals grown in diffusion limited medium

Single crystals of the title compound Ca (C₄H₅O₅)₂.10H₂O are grown in silica gel using controlled chemical reaction method. Multifaceted single crystals of size up to 8 × 4 × 2 mm³ are obtained. Powder X‐ray Diffraction (XRD) pattern of the grown crystal and the Fourier Transform Infra‐Red (FTIR) spectrum in the range 400–4000 cm^–1 are recorded. The vibrational bands corresponding to different functional groups are assigned. Thermal decomposition stages observed in the Thermo‐gravimetric (TG) and Differential Thermal Analysis (DTA) studies are discussed. A six‐stage thermal decomposition scheme is proposed for the compound. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth and spectral analysis of Dy3+ and Er3+ doped KPb2Cl5 as a mid‐infrared laser crystal

This paper reports crystal growth and optical characteristics of dysprosium (Dy³⁺) and erbium (Er³⁺) doped mid‐infrared laser crystal ternary‐potassium‐lead‐chloride (KPb₂Cl₅). Two transparent crystals with good optical quality have been grown successfully by using the Bridgman technique,the largest crystal size reaches up to ∅︁10×60mm². Measurements of X‐ray diffraction(XRD) and absorption spectra were carried out. Based on Judd‐Ofelt theory, the intensity parameters Ω_t(t=2,4,6), the experimental and theoretical oscillator strengths have been obtained.The intensity parameters Ω_t(t=2,4,6) of Er³⁺:KPb₂Cl₅ were calculated to be Ω₂=5.10×10^‐20 cm², Ω₄=1.25×10^‐20 cm², Ω₆=0.83×10^‐20 cm², and the values for Dy³⁺:KPb₂Cl₅ were calculated to be Ω₂=6.26×10^‐20 cm², Ω₄=2.45×10^‐20 cm², Ω₆=0.04×10^‐20 cm² respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of cationic substitution on lattice constants and optical characterization in solution grown mixed crystals of potassium‐ ammonium zinc chloride

Mixed crystals of potassium‐ammonium zinc chloride in different concentrations were grown from aqueous solution employing the techniques of slow cooling and controlled evaporation. Powder x‐ray diffraction studies were carried out on the grown crystals. The comparison between lattice parameters a, b and c are experimentally determined and calculated by Vegad's law. The concentration of K⁺ ions in the crystals was measured by the atomic absorption technique. The crystal morphology changed considerably by increasing K⁺ concentration. The optical absorption coefficient (α) indicated strong influence changing concentration. The optical energy gap was found to decrease with increasing K⁺ concentration. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of bismuth tri‐iodide platelets by the physical vapor deposition method

The work reports the growth of single BI₃ crystals with platelets habit. Platelets were grown by physical vapor deposition (PVD) in a high vacuum atmosphere and with argon, polymer or iodine as additives. Crystals grew in the zone of maximum temperature gradient, perpendicular to the ampoule wall. Crystals grown with argon as additive show a very shining surface, have hexagonal (0 0 l) faces, sizes up to 20 x 10 mm² and thicknesses up to 100 μm. They were characterized by optical microscopy and scanning electron microscopy (SEM). Dendritic‐like structures were found to be their main surface defect. SEM indicates that they grow from the staking of hexagonal unities. Electrical properties of the crystals grown under different growth conditions were determined. Resistivities up to 2 x 10¹² Ωcm (the best reported value for monocrystals of this material) were obtained. X‐ray response was measured by irradiation of the platelets with a ²⁴¹Am source of 3.5 mR/h. A comparison of results according to the growth conditions was made. Properties of the crystals grown by this method are compared with the ones measured for others previously grown from the melt. Also, results for bismuth tri‐iodide platelets are compared with the ones obtained for mercuric and lead iodide platelets. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)