Linear and nonlinear optical properties of tris thiourea zinc sulphate single crystals

Optical absorption of tris thiourea zinc sulphate (ZTS) single crystals has been measured and its direct band gap was found to be 3.6 eV. Theoretical calculations were carried out to determine the linear optical constants such as extinction coefficient and refractive index. Further the optical nonlinearties of ZTS have been investigated by Z‐scan technique with He‐Ne laser at 632.8 nm. The nonlinear refractive index, absorption coefficient and third order susceptibility is found to be in the order of –5.36 ± 0.26 × 10^–12 cm²/W, 4.24 ± 0.21 × 10^–4 cm/W, 3.5 ± 0.17 × 10^–4 esu respectively. Thus optical characterization of ZTS reveals the various industrial application oriented properties of the material. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of pure and lithium doped L‐alanine single crystals for NLO devices

Single crystals of pure and lithium substituted L‐alanine are successfully grown by slow evaporation method at constant temperature of 32°C. The effect of lithium dopant on crystal properties has been studied. Powder and single crystal XRD analysis confirms the structure and change in lattice parameter values for the doped crystals. The crystals were characterized by solubility studies, density, melting point measurements, FTIR and UV‐Vis‐NIR techniques. Thermal and mechanical stability of crystals were tested by TGA/DTA and micro hardness analysis. NLO activity of the crystals is found to be increased in the presence of lithium ions. The dielectric constant and dielectric loss of the crystals were studied as a function of frequency. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of pure and Hg2+ doped thiosemicarbazide cadmium chloride crystals

Semiorganic single crystals of thiosemicarbazide cadmium chloride (TSCCC) and mercury ions doped thiosemicarbazide cadmium chloride were synthesized by slow solvent evaporation technique. The grown crystals were subjected to powder X‐ray analysis and both the crystals were found to crystallize in the monoclinic system. EDAX analysis was carried out for chemical analysis of the grown crystals. The UV‐Vis‐NIR spectrum shows that both the materials have wide transparency window in the visible and near IR region. The dielectric studies were carried out to estimate the dielectric constant and dielectric loss with respect to frequency for both the crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical and dielectric studies on succinic acid single crystals

Single crystals of ferroelectric succinic acid (SA) with very high degree of transparency were grown from aqueous solution by slow evaporation technique. Single crystal X‐ray diffraction analysis reveals that the crystal belongs to monoclinic system with the space group P2₁/c. Some physical parameters have been determined for grown crystal. The optical absorption study reveals the transparency of the crystal in the entire visible region and the cut off wave length was found to be 240 nm. The optical band gap is found to be 3.75 eV. The dependence of extinction coefficient (k) and refractive index (n) on the wavelength have also been reported. The presence of functional groups was determined qualitatively by using Fourier transform infrared spectrum (FTIR) from which force constant has been calculated. The dielectric constant was also studied as a function of frequency at room temperature and electrical conductivity has been calculated from the Cole‐Cole plot. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of pure and metal doped bis(thiourea) zinc chloride single crystals

Metal (Cd²⁺ and Cu²⁺) substituted single crystals of Bis(thiourea) zinc chloride (BTZC) are grown by slow solvent evaporation technique, with the vision to improve the physicochemical properties of the sample. Single crystal XRD studies of both pure and doped samples are carried out and the results are compared. Optical absorption and FTIR studies are performed to identify the UV cut‐off range and the presence of various functional groups in the grown crystals. The thermogravimetric (TG) analysis of metal doped BTZC indicates a marginal increase in the thermal stability of the crystals. The dielectric response of the samples have been studied in the frequency range 100 Hz to 5 MHz at room temperature and the results are discussed. Photoconductivity studies carried out on pure and metal doped BTZC crystals revealed the negative photoconducting nature. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of undoped,Sr2+‐, and Mn2+‐doped ammonium tetrachlorozincate

Crystals of ammonium tetrachlorozincate (AZC) undoped and doped with Sr²⁺ or Mn²⁺ in different concentrations were grown by the slow evaporation method from an aqueous solution. The crystal morphology changed considerably by doping. The dopant concentration in the crystals was measured by the atomic absorption technique. Slight changes in the unit cell parameters of AZC after doping with Sr²⁺‐ or Mn²⁺ have been detected. Optical absorption measurements indicated strong influence of Sr²⁺ and Mn²⁺ doping. The optical energy gap at room temperature decreased continuously with increasing Sr²⁺ and Mn²⁺ concentration but with two different rates. The dc conductivity was also measured as a function of temperature for the undoped and two samples doped with 0.144 Sr²⁺ and 0.191 Mn²⁺ and the results were compared. Positions possibly occupied by Sr²⁺ and Mn²⁺ cations in AZC lattice have been identified. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical absorption spectra and related parameters of ammonium zinc chloride crystal in the antiferroelectric and commensurate phases

Optical absorption along the three crystallographic axes of (NH₄)₂ZnCl₄ single crystals is reported over a temperature range from 276 K to 350 K. Our results clearly confirm the antiferroelectric to commensurate phase transition at 319 K. Analysis reveals that at the absorption edge the type of transition is the indirect allowed one. The indirect band gaps at various temperatures are determined and their temperature dependence is estimated in the antiferroelectric and commensurate phases. Optical parameters related to the temperature dependence of the energy gap are evaluated. The single‐effective oscillator model was used to describe the imaginary part of the dielectric constant, which facilitate calculation of the dipole moment parameters. The steepness parameter is given, its value is used to estimate the temperature dependence of the indirect energy gap and the result is compared with that calculated graphically. In the region of the absorption edge, the absorption coefficient obeys Urbach's rule. Urbach characteristic parameters are determined and their temperature dependence is investigated. Correlation between different parameters is considered. Most of the results confirm the optical isotropic nature of AZC crystals. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of trivalent ions doped PbWO4 crystals and their scintillation properties

Undoped and series of trivalent ions(including La, Y, Gd and Tb) doped PWO crystals were grown from 5N raw materials by using Czochralski technique. Trivalent ions doping improved the transmittance, fast components of luminescence and radiation damage resistance for compensating structure defects. Corresponding, the fraction of light yield at shorter collecting time was increased. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Temperature‐tuned band gap energy and oscillator parameters of Tl2InGaSe4 semiconducting layered single crystals

The optical properties of Tl₂InGaSe₄ layered single crystals have been studied through the transmission and reflection measurements in the wavelength range of 500‐1100 nm. The analysis of room temperature absorption data revealed the presence of both optical indirect and direct transitions with band gap energies of 1.86 and 2.05 eV, respectively. Transmission measurements carried out in the temperature range of 10‐300 K revealed that the rate of change of the indirect band gap with temperature is γ = – 4.4 × 10^‐4 eV/K. The absolute zero value of the band gap energy was obtained as E_gi(0) = 1.95 eV. The dispersion of the refractive index is discussed in terms of the single oscillator model. The refractive index dispersion parameters: oscillator wavelength and strength were found to be 2.53 × 10^–7 m and 9.64 × 10¹³ m^–2, respectively. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Specific features of the optical spectra in Tl2In2S3Se layered single crystals

The optical properties of Tl₂In₂S₃Se layered single crystals have been studied by means of transmission and reflection measurements in the wavelength range of 450‐1100 nm. The analysis of the absorption data revealed the presence of both optical indirect and direct transitions with energy band gaps of 2.16 and 2.42 eV, respectively. The observed coexistence of indirect and direct energy band gaps is related to the anisotropy of the Tl‐containing layered crystals. The dispersion of the refractive index is discussed in terms of the Wemple‐DiDomenico single‐effective‐oscillator model. The refractive index dispersion parameters: oscillator energy, dispersion energy, oscillator strength and zero‐frequency refractive index were found to be 4.78 eV, 43.58 eV, 13.18 × 10¹³ m^–2 and 3.18, respectively. From X‐ray powder diffraction study, the parameters of monoclinic unit cell were determined. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical and dielectric studies on pure and Ni2+, Co2+ doped single crystals of bis thiourea cadmium chloride

Good quality single crystals of Ni²⁺, Co²⁺ ions doped Bisthiourea Cadmium Chloride (BTCC) are some of the excellent and efficient non‐linear optical materials grown from aqueous solution by slow evaporation method. The lattice parameters of the grown crystals are determined by single crystal X‐ray analysis. UV spectral analyses on these samples reveal the improved transparency of the doped crystals ascertaining the inclusion of metal ion in the lattice. FTIR spectral analysis carried out on the materials confirm the presence of functional groups. Dielectric measurements reveal that the dielectric constant of pure and doped crystals decreases with increase of frequency. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mechanical properties of organic alkali metal and ammonium hydrophthalate single crystals

The mechanical parameters characterizing the deformation and fracture of acid salts of orthophtalic acid (alkali metals and ammonium hydrophthalates) have been determined. It is shown that the mechanical properties of these crystals are considerably anisotropic and can be either deformed plastically, form kink bands, or undergo brittle fracture depending on the direction of the compression axis with respect to the cleavage plane.     

Habit modification and improvement in properties of potassium hydrogen phthalate (KAP) crystals doped with metal ions

Potassium hydrogen phthalate (KAP) single crystals were grown by slow evaporation and slow cooling techniques. The growth procedure like temperature cooling rate, evaporation rate, solution pH, concentration of the solute, supersaturation ratio etc., has been varied to have optically transparent crystals. Efforts were made to dope the KAP crystals with rubidium, sodium and lithium ions. The dopant concentration has been varied from 0.01 to 10 mole percent. Good quality single crystals were grown with different concentrations of dopants in the mother phase. Depending on the concentration of the dopants and the solution pH value, there is modification of habit. Rubidium ions very much improve the growth on the prismatic faces. The transparency of the crystals is improved with rubidium and sodium doping. The role of the dopants on the non‐linear optical performance of KAP indicates better efficiency for doped crystals. The grown crystals were characterized with XRD, FT‐IR, chemical etching, Vickers microhardness and SHG measurements. The influence of the dopants on the optical, chemical, structural, mechanical and other properties of the KAP crystals was analysed. © 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Thermoelectric properties of Tl‐doped Bi2Se3 single crystals

The single crystals of the ternary system based on Bi_2‐xTl_xSe₃ (nominaly x = 0.0‐0.1) were prepared using the Bridgman technique. Samples with varying content of Tl were characterized by the measurement of lattice parameters, electrical conductivity σ_⊥c , Hall coefficient R_H (B∥c), and Seebeck coefficient S (ΔT ⊥c). The measurements indicate that by incorporating Tl in Bi₂Se₃ one lowers the concentration of free electrons and enhances their mobility. This effect is explained in terms of the point defects in the crystal lattice – formation of substitutional defects thallium on the site of bismuth Tl_Bi and the decrease of concentration of selenium vacancies V_Se⁺². We also discuss the temperature dependence of the power factor σS² of the samples. Upon the thallium doping we observe a significant increase of the power factor compare to the parental Bi₂Se₃. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical imaging of the growth kinetics and polar morphology of zinc tris(thiourea) sulphate single crystals

Growth kinetics of zinc tris(thiourea) sulphate (ZTS) single crystals was imaged in two different growth geometries using laser shadowgraphy technique. Growth rates of the {010} and {001} faces were computed as a function of supersaturation. The time evolution of polar morphology of ZTS crystal based on the growth rates is presented. Except (00 ) face, all the other three faces are found to have a dead zone resulting in large induction period of growth. The anisotropy in the growth rates of the (001) and (00 ) faces was very high, resulting in polar morphology. Different chemical environments on two sides of the (001) slice are suggested as the possible cause for the polar morphology of the crystals. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural,electrical, thermal and optical properties of the nonlinear optical crystal L‐Arginine Fluoride

Single crystals of L‐Arginine Fluoride (LAF) have been grown by the slow evaporation technique, and the crystalline perfection was studied by HRXRD. Optical absorption studies reveal the lower cut off wavelength (280 nm) and the band gap (5.1 eV). The dielectric constant and dielectric loss have been measured as a function of frequency (42 Hz–5 MHz) and temperature (307‐368K) and the activation energy is 77 μeV. The thermal transport properties such as thermal conductivity (0.88 ± 0.02 W/mK) and specific heat capacity (482±24 J/kg/K) have been estimated by the photopyroelectric technique. The nonlinear refractive index n₂, is found to be of the order of 10⁻¹³ cm²/W by the Z‐scan technique.     

Effect of different metal ions on structural,thermal, spectroscopic and optical properties of ATCC and ATMC single crystals

A novel metal‐organic coordination complex nonlinear optical crystals, tri‐allylthiourea cadmium chloride [(CdCl₂(AT)₃] and tri‐allylthiourea mercury chloride [(HgCl₂(AT)₃] abbreviated as ATCC, ATMC (AT is Allylthiourea i.e.,CH₂=CHCH₂NHCSNH₂) has been synthesized and grown as single crystals. It was synthesized in deionised water and further recrystallized to improve its purity. Single crystals of the allylthiourea co‐ordination complex nonlinear optical crystals tri allylthiourea cadmium chloride (ATCC) with dimensions of 14x14x10 mm³ and tri allylthiourea mercury chloride (ATMC) with dimensions of 15x15x12 mm³ were grown successfully from aqueous solution by solvent evaporation as well as by temperature lowering method. It exhibits powder SHG efficiencies higher than that of a well known organic NLO crystal Urea. The solubility of the as grown crystals was estimated from the aqueous solution and the effect of different metal ions on the grown crystals, structural, thermal, spectral and optical properties were analyzed. XRD studies the reveals the same structure of both materials. Influence of the different central metal (Cd and Hg) atoms, changing the thermal properties of the materials when NLO complexes formed with the common ligand allylthiourea. The metal co‐ordination was confirmed form the spectroscopic analysis. From the UV transmittance studies, red shift was from the transparency cut‐off wavelengths. The value is 285nm for ATCC is and is 335nm ATMC, Non‐linear an optical study confirms the suitabilities of the as grown crystals for the non linear optical applications. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrical and optical properties of Co doped TlGaS2 crystals

In this study, Co doped TlGaS₂ single crystals which belongs to the class of A^IIIB^IIIX₂^VI have been investigated by means of XRD, temperature dependent dark and illuminated conductivity, Space Charge Limited Currents and absorption measurements. The room temperature conductivity and trap concentration values were about 10^‐8 (Ω‐cm)^‐1 and 7.5 × 10¹³ cm^‐3, respectively. From the temperature dependent conductivity measurements, two activation energies namely 271 and 12 meV have been determined in the high and low temperature regions, respectively. The trap level at 271 meV that was determined by the dark temperature dependent conductivity measurement has also been verified by Space Charge Limited Currents analysis. The absorption measurements have showed that the layered compound had indirect and direct band gaps and the values were determined to be 2.49 and 2.56 eV, respectively. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,growth and characterization of single crystals of pure and thiourea doped L‐glutamic acid hydrochloride

L(+)Glutamic acid hydrochloride [HOOC (CH₂)₂CH(NH₂) COOH·HCl], a monoamino dicarboxylic acid salt of L‐Glutamic acid was synthesized and the synthesis was confirmed by FTIR analysis. Solubility of the material in water was determined. Pure and Thiourea doped L‐Glutamic acid hydrochloride crystals were grown by low temperature solution growth using solvent evaporation technique. XRD, UV‐Vis‐NIR analyses were carried out for both pure and thiourea doped crystals. The crystals were qualitatively analyzed by EDAX analysis and the presence of thiourea was confirmed. The cell parameters of L‐Glutamic acid hydrochloride have been determined as a = 5.151 Å, b = 11.79 Å, c = 13.35 Å by X‐ray diffraction analysis and it crystallizes in orthorhombic space group P2₁2₁2₁. UV‐Vis‐NIR spectra analysis showed good optical transmission in the entire visible region for both pure and doped crystals. Micro hardness of both pure and doped crystals has been determined using Vickers micro hardness tester. The SHG efficiencies of both pure and doped crystals were determined using Kurtz powder test and pure L‐Glutamic acid hydrochloride crystal was found to possess better efficiency than thiourea doped L‐Glutamic acid hydrochloride crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of lithium ions on the NLO properties of KDP single crystals

Potassium Dihydrogen Phosphate (KDP) and its isomorphous deuterated form are popular due to their applications in frequency converters and electro‐optic modulation. Different attempts have been made to dope KDP with inorganic additives, organic materials and amino acids. Since many of the metal ions possess more electro negativity which increases the non centrosymmetry, it is of interest to dope them in KDP. The influence of lithium ion (Li⁺) on NLO properties of KDP crystal has been studied in the present investigation. Single crystal of Lithium ion doped Potassium Dihydrogen Phosphate (KDP) was grown by slow evaporation technique. The enhancement in SHG efficiency after addition of ion Lithium (Li⁺) was observed by Kurtz Powder SHG test. It was found that the SHG efficiency of KDP after addition of Lithium ion is 1.33 times more than pure KDP. The crystal structure and cell parameters of grown crystal were determined by X‐ray diffraction. The Energy Dispersive X‐ray analysis (EDAX) gives the chemical composition of grown crystal. The functional groups were identified by FT‐IR spectral analysis. The presence of Lithium in the material of grown crystal was detected by Atomic absorption spectroscopy (AAS). The optical absorption and transmission studies were done by UV‐Visible spectral analysis. The grown crystal was subjected to thermogravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC). (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)