High-order picosecond SRS and self-SRS generation in Nd3+-doped CaMoO4, SrMoO4, and SrWO4 laser crystals

The results of a stimulated Raman scattering (SRS) spectroscopy study of Nd³⁺-doped CaMoO₄, SrMoO₄, and SrWO₄ crystals are presented. All the wavelengths of the Stokes and anti-Stokes generation observed in these crystals are identified. For the first time, the self-SRS conversion of the emission frequency of activator Nd³⁺-ions is attained in these lasing molybdates and tungstate with scheelite-type structures.     

Absorption and electrical conductivity of CaMoO4 crystals

The electrical conductivity σ of CaMoO₄ crystals was investigated between room temperature and 850°C. The mobility v_v and the diffusion coefficient D_v of the O⁻ ion vacancies have been derived from σ: v_vT = 3300 exp (−1.52 eV/kT) cm² K/Vs, D_v = (0.1…1) × exp (−1.52 eV/kT) cm²/s. An absorption occuring in crystals which are reduced or X-irradiated at low temperatures is dichroitic and caused by Mo⁵⁺ ions. For measurement in c direction the oscillator strength of the 680 nm absorption band is found to be about 0.1.     

Growth and characterization of mixed neodymium praseodymium oxalatze decahydrate crystals in silica gel

Mixed single crystals of neodymium praseodymium oxalate decahydrate were grown from silica gel by controlled reaction of rare earth nitrates with oxalic acid. The crystals were characterized using X-ray powder diffraction and optical absorption studies.     

Growth of different habits of lead bromide crystals in silica gel by the new gel technique

Lead bromide crystals of high optical perfection and of different habits have been grown in silica gel by new gel technique starting from colloidal lead tartrate and KBr solution. pH is found to be not a factor for habit modification. Certain habits of the grown crystals exhibit interesting surface features. The growth conditions have been optimized and the various aspects of the growth process have been widely investigated.     

Factors influencing the periodic precipitation of BaMoO4 crystals in silica gel

Influence of electric and magnetic fields on the periodic precipitation of BaMoO₄ crystals in Silica gel has been discussed. The retarding effect of gel density on the advancing precipitation front has been qualitatively analysed. The role of impurity on the formation of rings has been investigated.     

Growth and characterization of pure and doped lead hydrogen phosphate single crystals in silica gel

Following the chemical reaction method pure and doped lead hydrogen phosphate single crystals were grown in silica gel using different gel density, various concentrations of phosphoric acid, and lead nitrate solutions. As the gel pH plays an important role in the formation of different H₃PO₄ species in the phosphoric acid system, the pH range in which HPO ions dominate, was considered which in turn in necessary for the growth of lead hydrogen phosphate crystals. Characteristics of these crystals were carried out by infrared spectral analysis and microhardness study.     

Growth of crystals of calcium sulphate in silica gel in presence of additive and their characterisation

Procedure for the growth of calcium sulphate dihydrate crystals in silica gel, in the presence of barium chloride as additive, is described. Optimum conditions for the growth of good quality crystals are worked out. The crystals are characterised by laser Raman spectroscopy, infrared spectroscopy, thermogravimetric analysis and Atomic absorption spectroscopy. It is shown that crystals in the presence of the additive have a greater degree of perfection than those without additive. Amount of water in the crystals is estimated as 20.97%. Presence of calcium and absence of barium in the crystals are indicated.     

Observations on the growth of NiMoO4 crystals in Silica gel media

Growth of NiMoO₄ crystals by gel method has been described. By manipulating the condition of growth parameters, crystals of fairly large dimensions have been obtained at ambient temperature. The crystal faces are examined by optical and scanning electron microscopy and thus a two-dimensional layer growth mechanism for the development of the faces have been proposed.     

Growth of manganese tartrate trihydrate in silica gel

Growth of manganese tartrate trihydrate crystals in silica gel media with manganese chloride and manganese sulphate as the reactant is attempted. The reason for the occurrence of platelets along with dendrites in the case of manganese sulphate is discussed. IR, X-ray, atomic absorption and thermogravimetric techniques are employed to characterize the grown crystals and the results are discussed.     

Growth of calcium phosphate crystals in Silica gel

The results of a study of the crystal growth of calcium phosphates in silica gel employing double diffusion system with CaCl₂ and KH₂PO₄ aqueous solutions are reported. Liesegang rings, spherical crystalline agglomerates and brushite dendrites are formed near the CaCl₂ solution. It was found that the agglomerates consist of octacalcium phosphate and hydroxyapatite crystals with the predominance the former.     

Growth of Te(OH)6Na2HPO4 · H2O single crystals in silica gel and their characterization

Single crystals of Te(OH)₆Na₂HPO₄ · H₂O were grown in silica gel medium using single-test tube diffusion method. Hexagonal pyramidal and hexagonal tabular single crystals were obtained. Crystals were characterized by IR, X-ray, and Raman studies.     

Growth of lanthanum heptamolybdate crystals by gel technique

The growth of single crystals of lanthanum heptamolybdate is achieved by allowing controlled diffusion of La ions through silica gel using the system La(NO₃)₃ MoO₃ NH₄OH HNO₃–Na₂SiO₃. The reaction mechanism leading to the growth is reported. Mechanism of crystallization of La heptamolybdate is discussed. Formation of Liesegang rings consisting of La heptamolybdate crystals in the system is reported. It is observed that concentration programming and seeded growth enhances the size of crystals. The crystals grown in the system are single crystal platelets exhibiting squarish or octagonal facets. Some crystals exhibit a spherulitic morphology.     

Characterization of pure and doped potassium hydrogen tartrate single crystals grown in silica gel

Growth of pure‐, sodium‐ and lithium‐ doped potassium hydrogen tartrate single crystals by gel technique is reported. Growth conditions conducive for the growth of single crystals are worked out. The crystals are characterized by using powder XRD, SEM, FTIR, AES, EDAX, CH analysis and thermoanalytical techniques. The stoichiometric composition for the grown crystals are established as KHC₄H₄O₆.H₂O, (K)_0.98(Na)_0.02.H₂O and (K)_0.94(Li)_0.06HC₄H₄O₆.H₂O. Doping of sodium and lithium in the pure potassium hydrogen tartrate single crystals is found to influence the size, perfection, morphology, crystal structure and the thermal stability of crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of gel grown calcium pyrophosphate tetrahydrate crystals

Formation of calcium pyrophosphate dihydrate (CPPD) crystals in soft tissues such as cartilage, meniscus and synovial tissues lead afflictions. The appearance of these crystals in the synovial fluid give rise to acute arthritis attack, which is known as pseudo‐gout. The growth of calcium pyrophosphate crystals in gel medium can mimic the growth in a body. In the present study, calcium pyrophosphate tetrahydrate (CPPT) crystals are grown by a single diffusion gel growth technique and characterized by powder XRD, FT‐IR spectroscopy, TGA, kinetic and thermodynamic studies of dehydration and dielectric studies. Monoclinic crystals structure, presence of P‐O bonds and four water molecules are confirmed from powder XRD, FT‐IR and TGA studies, respectively. The dielectric investigation suggests the reduction in dielectric constant with increase in frequency. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of lead(II)chloride single crystals grown in silica gel

Acousto‐optical materials play an important role in acousto‐optic devices as acousto‐optic modulators. Lead(II) chloride is an acousto‐optical material, having high figure of merit approximately ten times greater than that of lead molybdate, which is an efficient acousto‐optical material. It also possesses high birefringence, low attenuation coefficient, wide transparency range and good mechanical properties. This paper discusses in detail, the growth of single crystals of lead(II) chloride in silica gel by the process of diffusion in a highly acidic medium. Needle‐type lead(II) chloride crystals have been obtained. The crystal system is confirmed to be orthorhombic by powder X‐ray diffraction analysis. To study the optical transparency of the grown crystal, the transmission spectrum has been recorded in the range 190 – 1100 nm. Thermal stability of the crystal is also studied. Results are discussed in detail. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of octacalcium phosphate and dicalcium phosphate dihydrate crystals in silica gels

The crystallization of octacalcium phosphate (OCP) and dicalcium phosphate dihydrate (DCPD) have been studied at ambient temperature in silica gel using double diffusion system. The first stage of evolution of the OCP spherulites as well as their growth have been observed by optical microscopy. The growth rate of the OCP spherulites under stable external conditions was constant. The formation of DCPD crystals has been observed in the last stages of experiments.     

Growth aspects of barium oxalate monohydrate single crystals in gel medium

Single crystals of barium oxalate monohydrate (BaC₂O₄.H₂O, BOM) were grown in pure form by controlled diffusion of Ba²⁺ using the gel technique at different temperatures. Starting from aqueous Ba²⁺ chloride (BaCl₂) and acetic acid (C₂H₂O₄) in gel, this method offers a low‐cost and an easiest alternative to other preparation methods for the production of barium oxalate bulky single crystals. The optimal conditions for the growth of BOM crystals in silica gel were found by investigating different growth parameters such as gel pH, gel aging and crystallization temperature. Irrespective of all such crystallization environments, growth rate of the crystals were initially less and then exhibited supersaturation effect leading to non‐linearity. Gel aging and temperature has profound effect on nucleation density that resulted less number of crystals of maximum size in the gel matrix. Perfect single crystals were grown on gels of higher pH. The macropore morphology and porosity was controlled by changing age of the gel. It has been found that temperature has a fabulous effect in controlling the nucleation density by altering the supersaturation conditions for the formation of critical nuclei. The entire growth kinetics informed that the grown crystals were derived by the one dimensional diffusion controlled process. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)