Optical and electro-optical properties of ZnMgSe single crystals

The optical and electro-optical properties of large-sized (diameter, 20 mm; length, 70 mm) single crystals of Zn_{1 ? x}Mg_xSe (x ～ 0.5) semiconductor solid solutions are investigated. The crystals are grown by the vertical Bridgman-Stockbarger method. It is found that, for ZnMgSe single crystals with a magnesium content up to 25 at. %, the modulus of the difference between the electro-optical coefficients |r₁₃ ? r₃₃| at a wavelength of 0.63 μm is equal to (1.1 ± 0.22) × 10^?12 m/V, which is comparable in order of magnitude to the difference in the electro-optical coefficients for classical hexagonal A^IIB^VI compounds, such as CdS and CdSe. It is shown that single crystals of ZnMgSe solid solutions are promising materials for use in the fabrication of electro-optical modulators, λ/4-and λ/2-wavelength plates, and multifunctional optical elements operating in the range of high-intensity radiation of CO and CO₂ lasers.     

Temperature dependences of the electrical conductivity and hall coefficient of indium telluride single crystals

Conductivity type, carrier concentration and carrier mobility of InTe samples grown by Bridgmann technique were determined by the Hall effect and electrical conductivity measurements. The study was performed in the temperature range 150–480 K. Two samples with different growth rate were used in the investigation. The samples under test were P-type conducting, in accordance with previous measurements of undoped material. The Hall coefficient was found to be isotropic yielding room temperature hole concentration in the range 10¹⁵ – 10¹⁶ cm⁻³. The hole mobilities of InTe samples were in the range 1.17 × 10³ – 2.06 × 10³ cm²/V · sec at room temperature. The band – gap of InTe determined from Hall coefficient studies has been obtained equal to 0.34 ev. The scattering mechanism was checked, and the electrical properties were found to be sensitive to the crystal growth rate.     

Anisotropy of optical absorption in layered single crystals

The optical energy gap of Re doped MoSe₂ single crystal Mo_0.995Re_0.005Se₂ has been measured at room temperature near the fundamental absorption edge. The incident light was kept normal to the basal plane i.e. along the c‐axis of the grown crystals. Results have been given on the basis of two and three dimensional models. Both direct and indirect transitions are involved in the absorption process. The indirect transition was found to be allowed with two phonons involved in the process. The three dimensional model and not the two dimensional could be used to describe the optical properties of Re doped MoSe₂ single crystal. Also, the optical energy gaps depend upon the amount of the intercalating Re material. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Temperature dependence of lattice parameters of langasite single crystals

To determine the coefficient of thermal expansion of trigonal langasite (La₃Ga₅SiO₁₄) the two independent lattice parameters a and c are measured over a temperature range of 800 °C using X‐ray diffraction on single crystal samples. From the given nonlinear temperature dependence the linear and quadratic thermal coefficients of expansion α₁₁, β₁₁ and α₃₃, β₃₃ for the two lattice parameters a and c could be deduced. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characteristics of HgGaInS4 single crystals

Single crystals of the HgGaInS₄ layered compound were grown by the iodine transport technique. Results of their optical, photoelectric, and radiative properties' study are presented. The band gap and the binding energy of holes on the sensitizing centres were determined to be E_g = 2.41 eV and E_a = 0.2 eV, respectively. A presence of quasi-continuously distributed states was stated which are responsible for the exponential segment of the absorption edge and which take part in the radiative recombination.     

Growth and optical characteristics of Ce-doped and Ce : Na-codoped BaLiF3 single crystals

Ce-doped and Ce : Na-codoped BaLiF₃ single crystals were grown by the Czochralski technique under reactive atmosphere. Na⁺-ions, used as a charge-compensating impurity, compete with Ce³⁺-ions for Ba²⁺ sites in the host, reducing the Ce³⁺ incorporation and degrading the mechanical integrity of crystals. Ce-doped BaLiF₃ showed potential for UV tunable lasers.     

Anisotropy of the optical suppression of the magnetoplastic effect in NaCl single crystals

Anisotropy of the plane-polarized light effect on magnetosensitive point defects in NaCl crystals has been observed. The data obtained may yield the information on the symmetry of the electronic states of these defects.     

Temperature dependence of the dielectric parameters of nonstoichiometric SrTiO3 single crystals

The results of experimental studies of the temperature dependence of the low-frequency permittivity ε ₀ and the loss tangent taδ of nominally undoped and doped single crystals of strontium titanate at T = 10–300 K are given. The samples were doped with ions of iron-group metals (V, Mn, Fe, Co) and/or ions of rare earth metals (Pr, Nd, Sm, Tm) with concentrations of 10^?3?5 × 10^?1 at %. Anomalous temperature dependences ε₀ T and tanδ(T) were found for a number of samples. The anomalies found were attributed to the violation of stoichiometry of the single crystals under study and the transition of some fraction of Ti⁴⁺ ions to the Ti³⁺ state.     

Angular dependences of transmission spectra of chiral liquid crystals

Transmission spectra of chiral nematic liquid crystals (CNLCs) and chiral smectic С* liquid crystals (CSLCs) are studied in a wide range of angles of light propagation with respect to the direction of the helical structure axis. To this end, both a planar LC cell and a cell consisting of two substrates in the form of rectangular prisms (30° × 60° × 90°) were used, which allowed measurements of the transmission spectra at the light propagation at angles up to 65° with respect to the helical axis direction. The transmission spectra are numerically simulated; the results are in good agreement with the experimental spectra. A technique for determining the tilt angle of molecules in smectic layers is proposed based on the comparative analysis of experimental and calculated transmission spectra of CSLC.     

Studies on the growth and optical characterization of dysprosium gadolinium oxalate single crystals

Preparation and optical characterization of dysprosium gadolinium oxalate (DGO) single crystal is reported. The crystals were grown using silica gel technique, by the controlled reaction of rare earth nitrates with oxalic acid. Crystals were characterized using X‐ray powder diffraction, optical absorption and fluorescence studies. Radiative transition probability, fluorescence branching ratio and radiative lifetime of Dy³⁺ in the crystal are evaluated by the parameterization of the absorption spectrum by the Judd‐Ofelt theory. The recorded fluorescence spectrum showed two well resolved peaks at 480 nm and 571 nm and are assigned to the transitions from ⁴F_9/2 → ⁶H_15/2 and ⁶H_13/2 of Dy³⁺. Stimulated emission crossection and optical gain of these transitions are also evaluated. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Relation between the real structure and optical inhomogeneity of lithium niobate single crystals

Crystallography Reports - A real structure of lithium niobate single crystals has been studied by the etching method. A relationship between the real structure and the optical inhomogeneity...     

Growth and optical absorption studies on potassium dihydrogen phosphate single crystals

Growth of bulk nonlinear optical (NLO) single crystals gained new significance with the advent of solid‐state laser sources for opto‐electronic applications. An optically transparent crystal of potassium dihydrogen phosphate (KDP) has been grown from aqueous solution along (001) plane with the aid of modified growth assembly of Sankaranarayanan‐Ramasamy (SR) Method. The evaporation rate was controlled and single crystals of 5 mm diameter and 60 mm length with a growth rate 5 mm per day have been grown successfully. The improved transparency of grown crystal was investigated using DRS UV transmittance spectral analysis and the presence of functional groups in the grown crystal is confirmed using FTIR analysis. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Anisotropy of the optical absorption in layered single crystals of MoRe0.001Se1.999

Energy gap of MoRe_0.001Se_1.999 single crystal has been determined by fundamental absorption methods. The incident light was polarized along c‐axis of the crystals. The interpretion of the data is given within frameworks of two and three dimensional models. Both direct and indirect transitions are involved in the absorption process. The indirect transition was found to be allowed with two phonons participating in the process. The three dimensional model could be used to describe the optical properties of the single crystal. The energy gaps depend upon the amount of the intercalating Re material, which show the anisotropy of the chemical bonds. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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)     

Doping of KDP single crystals with cerium: Growth and optical properties

The features of doping of KDP crystals with cerium ions and organocerium complexes with alizarin complexon and arsenazo III have been investigated. It is established that “direct” doping by introducing cerium salts into the initial solution cannot be implemented. The effect of organometallic complexes of cerium on the crystal growth has been studied. Organocerium complexes predominantly enter the prismatic or pyramidal growth sectors. It is shown that the complex arsenazo III + Ce blocks the growth of the prismatic sector. Cerium-doped KDP crystals exhibit a photoluminescence band peaking at the wavelength λ_max= 350 nm.     

X-ray,optical and electrical study of melt-grown CdI2 single crystals

CdI₂ has been purified using the zone-refining technique by giving 20 passes. Single crystals grown from the starting material showed arcing in the X-ray oscillation photographs whereas it is absent in the crystals grown from the zone refined material. These crystals are found to be of the 4 H type. DC conductivity studies were made on these crystals at various stages of purification. The surface morphology of these crystals have been studied using an optical microscope.     

Oriented growth of large size calcium fluoride single crystals for optical lithography

We report (1 1 1), (1 1 0) and (1 0 0) growth of CaF₂ by the vertical Bridgman method. Crystals up to 250 mm diameter were grown and various growth parameters such as growth rate, temperature gradient and post-growth cooling rate were studied. It was found that the growth rate and the cooling rate are slower for the larger diameter crystals with a fixed temperature gradient. These growth parameters were optimized for growing the crystals along specific orientation after realizing that CaF₂ has a tendency to grow along an orientation close to 1 1 0. Degradation in optical transmittance was evaluated by irradiating the crystal to γ-rays up to a dose of 10⁵ rad. Optimized scavenger addition resulted in crystals with better radiation resistance and excellent VUV transmittance.     

Comparative optical absorption and photoreflectance study of n-type CuInSe2 single crystals

Optical absorption spectra in the photon energy range from 0.4 to 1.2 eV and photoreflectance spectra in the range of the fundamental edge are measured on n-type CuInSe₂ single crystals. Photoreflectance spectroscopy yields the true gap energy while the near-edge absorption spectra are dominated by acceptor–to–conduction band transitions, the acceptor ionisation energy being about 80 meV. Based on intrinsic defect chemistry considerations this acceptor is ascribed to copper vacencies.