Rajesh Narayana Perumal

Near-infrared down-conversion in Yb3+:TiO2 for solar cell applications

Near-infrared emitting phosphors of ytterbium doped titania are synthesized by precipitation method using titanium tetrachloride as a raw material. X-ray diffraction technique is to analyze the structure, ultraviolet–visible diffuse reflectance spectroscopy to determine the band gap energy and photoluminescence spectroscopy to characterize the luminescence properties of the synthesis material. The HRSEM and HRTEM are used to measure the morphology structure of the sample. This sample is excited by ultraviolet irradiation, exhibits an intense band emission near NIR region between 2F5/2 and 2F7/2 transition of Yb3+ ions using photoluminescence spectroscopy. The observation discusses the possible energy transfer mechanism between TiO2 and Yb3+ ions. The results determine the synthesized material is adept for silicon based solar cells.

A software program to investigate the nucleation kinetics of solution grown crystals using MATLAB platform

Abstract A software program has been developed on the MATLAB platform, which is useful for studying the nucleation kinetics of crystals grown from solutions. Nucleation parameters such as interfacial energy ( σ ) , metastable zone width ( Δ T max ) , volume free energy ( Δ G v ) , critical energy barrier for nucleation ( Δ G ∗ ) , radius of the critical nucleus ( r ∗ ) and nucleation rate ( J ) of the crystals are determined from classical nucleation theory. The Metastable Zone Width (MZW) of the crystals is explored by using the relation based on solubility and enthalpy of nucleation. A new polynomial equation has been generated by this software program, and the results are checked with the experimental data of crystal growth/formation. Nucleation temperature as a function of supersaturation ratio was successfully evaluated using MZW. The equation relating to the nucleation kinetics and MZW can easily be solved with the help of a newly designed software program in the MATLAB platform. In addition, a program has been developed that highlights changes in nucleation parameters when the supersaturation ratio is changed. A plot of temperature vs energy barrier, nucleation rate and interfacial energy is also drawn. Program summary Program title: Nucleation Catalogue identifier: AERG_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AERG_v1_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 6305 No. of bytes in distributed program, including test data, etc.: 616560 Distribution format: tar.gz Programming language: MATLAB (MathWorks Inc.) version R2013a. Statistics Toolbox and Curve Fitting Toolbox required Computer: Any computer running MATLAB (MathWorks Inc.) Operating system: Tested on Windows XP, but generally it would work on any computer running MATLAB (MathWorks Inc.) RAM: 32 MB Classification: 8 Nature of problem: In crystal growth, the knowledge of nucleation thermodynamical parameters like interfacial energy, metastable zone width (supercooling temperature), volume free energy, critical energy barrier for nucleation, radius of critical nucleus and nucleation rates is essential for the growth of good quality bulk single crystals. In these parameters, metastable zone width determination is very useful for growth. Also some curve fitting tool is needed to obtain more information about nucleation kinetics. Solution method: In this program, an attempt has been made to calculate nucleation parameters theoretically to understand the role of these nucleation thermodynamical parameters for crystallization. A linear fit is done to calculate enthalpy of solution and polynomial fitting is used to derive the saturation concentration equation. Metastable zone width was calculated by the enthalpy–supersaturation relation. Supersaturation control is a decisive parameter for optimizing growth conditions during crystallization processes. The effects of metastable zone width and nucleation rate of crystals caused by changes in different supersaturation ratios were analyzed. Running time: Interactive and instantaneous.

Structural, thermal and optical properties of KTi0.92La0.08OPO4 and KTi0.94Nd0.06OPO4

KTi0.92La0.08OPO4 (KTP:La) and KTi0.94Nd0.06OPO4 (KTP:Nd) single crystals are grown using high temperature top seeded flux growth technique. The strain derived from doping is calculated from Williamson-Hall relation. The packing structure and lattice parameter of the grown crystals are analyzed using single crystal X-ray diffraction. The bonding, distortion and change in inter-atomic distances by strain effects of doping are assessed by Raman spectroscopy. Thermal stabilities of grown crystals are evaluated by specific heat capacity measurement. Pronounced high specific heat capacity is recorded as 1.16 J/gK at 498 K for KTP:Nd. Second harmonic generation intensities are measured for KTP:Nd and KTP:La single crystal.

Growth and characterization of propyl 4-hydroxybenzoate single crystal by vertical Bridgman technique

Abstract Organic material propyl 4-hydroxybenzoate (C10H12O3), single crystals, has been successfully grown by vertical Bridgman technique using the single and double wall ampoules. The grown crystal was confirmed by single crystal X-ray diffraction (XRD) and powder XRD analyses. Fourier Transform Infrared spectroscopy is used to identify the different functional groups. The thermal properties of the propyl 4-hydroxybenzoate were analysed. The single and double wall ampoules grown propyl 4-hydroxybenzoate crystals were also assessed by UV-vis-NIR, fluorescence and Vickers microhardness analyses. It is observed that the double wall ampoule gives better results than the single wall ampoule.

Growth of Organic Single Crystal by Transparent Vertical Bridgman Technique and Its Characterization

Organic single crystal of benzyl carbamate was grown by transparent vertical Bridgman technique. The grown crystal was subjected to single-crystal XRD, optical transmittance analysis, second harmonic generation analysis, laser damage threshold and photoconductivity analysis. The grown crystal cell parameters were confirmed by single-crystal X-ray diffraction analysis. From the UV–Vis–NIR transmittance spectrum analysis the cut off wavelength was found to be 275 nm. The second harmonic generation property of the powdered benzyl carbamate was confirmed by the emission of green light. The powder density value of benzyl carbamate crystal was found to be 0.955 GW/cm2. Benzyl carbamate showed positive photoconductivity nature and the calculated photosensitivity value was 2.84.

Crystal growth, structure analysis and characterisation of 2 - (1, 3 - dioxoisoindolin - 2 - yl) acetic acid single crystal

Single crystal of dielectric material 2 - (1, 3 - dioxoisoindolin - 2 - yl) acetic acid has been grown by slow evaporation solution growth method. The grown crystal was harvested in 25 days. The crystal structure was analyzed by Single crystal X - ray diffraction. UV-vis-NIR analysis was performed to examine the optical property of the grown crystal. The thermal property of the grown crystal was studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The dielectric measurements were carried out and the dielectric constant was calculated and plotted at all frequencies.