P. Murugakoothan

Natural dye extract of lawsonia inermis seed as photo sensitizer for titanium dioxide based dye sensitized solar cells.

Natural dye extract of lawsonia inermis seed were used as photo sensitizer to fabricate titanium dioxide nanoparticles based dye sensitized solar cells. Pure titanium dioxide (TiO2) nanoparticles in anatase phase were synthesized by sol-gel technique and pre dye treated TiO2 nanoparticles were synthesized using modified sol-gel technique by mixing lawsone pigment rich natural dye during the synthesis itself. This pre dye treatment with natural dye has yielded colored TiO2 nanoparticles with uniform adsorption of natural dye, reduced agglomeration, less dye aggregation and improved morphology. The pure and pre dye treated TiO2 nanoparticles were subjected to structural, optical, spectral and morphological studies. Dye sensitized solar cells (DSSC) fabricated using the pre dye treated and pure TiO2 nanoparticles sensitized by natural dye extract of lawsonia inermis seed showed a promising solar light to electron conversion efficiency of 1.47% and 1% respectively. The pre dye treated TiO2 based DSSC showed an improved efficiency of 47% when compared to that of conventional DSSC.

Comparison between pure and deuterated potassium acid phthalate (DKAP) single crystals

Single crystals of pure and deuterated potassium acid phthalate (DKAP) have been grown from aqueous solution by slow cooling method. The effect of deuterium on morphology and crystal properties has been studied. Powder X-ray diffraction analysis confirms the structure and changes in lattice parameter values for the deuterated crystals. The presence of deuterium in the crystal lattice has been confirmed by FTIR analysis. The DKAP crystals possess relatively lower hardness values than the pure crystals. The transmittance of DKAP is found to be higher than KAP crystals.

A new organic NLO material isonicotinamidium picrate (ISPA): crystal structure, structural modeling and its physico-chemical properties

A novel organic nonlinear optical (NLO) crystal, isonicotinamidium picrate (ISPA) was synthesized and grown by the slow evaporation method. Formation of the new crystalline compound was confirmed by a single crystal X-ray diffraction study. The title compound crystallizes in the monoclinic crystal system with the space group of P21/n. DFT was carried out to calculate the bond lengths and bond angles. Structural parameters obtained from single crystal XRD and DFT studies are in good agreement with each other. The frontier energy gaps calculated theoretically are useful to understand the charge transfer taking place in the molecule. Polarizability of the ISPA compound is found using Penn gap analysis and the Clausius–Mossotti equation. The UV-vis-NIR spectral study showed that the grown crystal is transparent in the entire visible region with the lower cut-off wavelength of 469 nm. The four independent tensor coefficients of dielectric permittivity were found to be e11 = 1.42, e22 = 4.62, e33 = 6.23 and e13 = 5.56 from the dielectric measurements. The titular compound ISPA is thermally stable up to 229 °C assessed by thermogravimetric and differential thermal (TG-DTA) analyses. The specific heat capacity of ISPA is found to be 3.49 J g−1 K−1. The laser induced surface damage threshold of the grown crystal was measured to be 0.22537 GW cm−2 for 1064 nm Nd:YAG laser radiation. Nonlinear refractive index (n2), absorption coefficient (β) and third order nonlinear susceptibility (χ(3)) were determined using the Z-scan technique. The optical limiting study revealed that the transmitted output power increases linearly with the input power up to the irradiance of around 3.25 mW mm−2.

Performance of Caesalpinia sappan heartwood extract as photo sensitizer for dye sensitized solar cells

A natural dye extracted from Caesalpinia sappan heartwood was used as photo sensitizer for the first time to fabricate titanium dioxide (TiO2) nanoparticles based dye sensitized solar cells. Brazilin and brazilein are the major pigments present in the natural dye and their optimized molecular structure were calculated using Density functional theory (DFT) at 6-31G (d) level. The HOMO-LUMO were performed to reveal the energy gap using optimized structure. Pure TiO2 nanoparticles in anatase phase were synthesized by sol-gel technique. The pure and natural dye sensitized TiO2 nanoparticles were subjected to structural, optical, spectral and morphological studies. Low cost and environment friendly dye sensitized solar cells were fabricated using natural dye sensitized TiO2 based photo anode. The solar light to electron conversion efficiency of Caesalpinia sappan heartwood extract sensitized dye sensitized solar cell is 1.1%.

Electronic structure, vibrational spectral and intervening orbital interactions studies of NLO material: guanidinium 4-nitrobenzoate.

Single crystals of guanidinium 4-nitrobenzoate (GPNB) have been grown by slow evaporation method. Grown crystals were characterized by FT-IR, FT-Raman, UV-Vis absorption and UV-Vis transmission spectroscopies. Crystal defects and surface morphology were studied by etching method. Dielectric properties of the crystal such as dielectric constant, dielectric loss and AC electrical conductivity as function of frequency (50 Hz-5 MHz) at two temperatures (35°C and 100°C) were measured. The frequency and temperature dependence of dielectric behaviour were investigated. The equilibrium geometry, vibrational spectral analysis, intramolecular charge transfer interactions using NBO method, first order hyperpolarizability, molecular electrostatic potential and frontier molecular orbital analysis for GPNB have been studied using density functional theory at B3LYP/cc-pVTZ level. Vibrational spectral study reveals the presence of moderate and weak N-H⋯O bonds in GPNB. NBO analysis also confirms the presence of intramolecular N-H⋯O hydrogen bonding and investigates the stability as well as the intervening orbital interactions. The electronic absorption spectrum of the gas and water phases of GPNB were simulated using time dependent density functional theory and NBO transitions for the three lowest excited states were assigned and studied.

Growth, spectral, anisotropic, second and third order nonlinear optical studies on potential nonlinear optical crystal anilinium perchlorate (AP) for NLO device fabrications

A new semiorganic nonlinear optical material anilinium perchlorate was grown by the slow evaporation technique using water as solvent. The solubility and meta stable zone width were determined. The anilinium perchlorate crystal belongs to orthorhombic system with noncentrosymmetric space group P2₁2₁2₁. The presence of various functional groups was identified by FT-IR FT-Raman spectrum. The morphology of the anilinium perchlorate crystal was studied. From this morphology, anilinium perchlorate crystal plate was cut along three prominent planes, such as (001), (010) and (20-1). The thermal stability of the crystal was determined using TG-DTA studies. The hardness, laser damage threshold, transmittance, reflectance, experimental refractive index of the crystal was found. The particle size dependent second harmonic generation efficiency for anilinium perchlorate was evaluated by Kurtz-Perry powder method using Nd:YAG laser, which established the existence of phase matching. The third order nonlinear refractive index and nonlinear absorption coefficient of the grown crystal were measured by Z-scan studies.

Crystal structure, molecular packing, FMO, NBO, nonlinear optical and optical limiting properties of an organic imidazolium diphenylacetate diphenylacetic acid single crystal

An organic nonlinear optical (NLO) crystal, imidazolium diphenylacetate diphenylacetic acid (IDA), was synthesized and grown by the slow evaporation method. Formation of the new crystalline compound was confirmed by single crystal X-ray diffraction study. The title compound crystallizes in the triclinic crystal system with the space group P. UV-vis-NIR spectral study showed that the grown crystal is transparent in the entire visible region with a lower cut-off wavelength of 275 nm. Density functional theory (DFT) calculations were carried out to calculate the frontier molecular orbitals and natural bonding orbitals of the IDA compound. The frontier energy gaps calculated theoretically were useful to understand the charge transfer taking place in the molecule. The natural bonding orbital analysis provides a convenient basis for the investigation of the charge transfer or conjugative interactions in the molecular system. Vickers microhardness study revealed that the title material belongs to the soft material category. The values of fracture toughness, brittleness index and yield strength have also been calculated for Palmqvist and median types of cracks. The title compound IDA is thermally stable up to 201 °C, as assessed by thermogravimetric and differential thermal (TG-DTA) analyses. The specific heat capacity of IDA is found to be 3.25 J kg−1 K−1 at 65 °C. The laser induced surface damage threshold of the grown crystal was measured to be 0.2645 GW cm−2 with 1064 nm Nd:YAG laser radiation. The nonlinear refractive index (n2), absorption coefficient (β) and third order nonlinear susceptibility (χ(3)) were determined using the Z-scan technique. An optical limiting study revealed that the transmitted output power increases linearly with the input power up to an irradiance of around 3.6 mW cm−2.

Green synthesis of Ag and the effect of Ag on the efficiency of TiO2 based dye sensitized solar cell

Green synthesis of silver nanoparticles (AgNPs) was carried out using the aqueous extract of Carcia papaya (commonly known as papaya) leaves as reducing and capping agent. The synthesized AgNPs colloid was mixed with titanium dioxide slurry to produce Ag:TiO2 nanocomposite. The as-synthesized AgNPs and Ag:TiO2 nanocomposite were characterized for structural, optical and morphological studies. Dye sensitized solar cells (DSSCs) were fabricated with pure TiO2 and Ag:TiO2 nanocomposite photoanodes using N719 dye and their performance was investigated. The power conversion efficiency of Ag:TiO2 nanocomposite DSSC is increased by about 33.5% when compared to the efficiency of the pure TiO2 DSSC. The electrochemical impedance spectroscopic measurements showed that Ag:TiO2 nanocomposite film effectively reduce the charge transfer resistance and also increased the lifetime of the electron.

Optimization, frontier molecular orbitals and dielectric studies on 2,6DiaminopyridiniumTosylate single crystals

An organic nonlinear optical (NLO) crystal, 2,6diaminopyridiniumtosylate (2, 6DPT) was synthesized and grown by the slow evaporation method. Formation of the crystalline compound was confirmed by single crystal X-ray diffraction study. The title compound (2, 6DPT) crystallizes in the monoclinic crystal system with space group, P21/c. The optimized molecular geometry and frontier molecular orbitals were obtained using density functional theory. The dielectric constant of the crystal was measured as a function of frequency for different temperatures and results are discussed.

Synthesis, Structural, Optical, Morphological and Elemental Characterization of CTAB Capped CdS Quantum Dots by Facile Chemical Precipitation Technique

In the present work, we report synthesis of CTAB capped cadmium sulphide quantum dots (CdS QDs) employing facile chemical precipitation technique in non aqueous medium at room temperature. Cadmium nitrate tetra hydrate and sodium sulphide flakes and cetyltrimethyl ammonium bromide (CTAB) was used as a precursors and capping agent respectively. The Powder X-Ray Diffraction (PXRD) confirms the hexagonal wurtzite structure and Field Emission Scanning Electron Microscopy (FESEM) shows the nanocrystalline nature. FESEM images showed a distribution of spherical particles with the diameter of 5.6–7.8 nm with the mean diameter of 7.1 nm. The change in band gap with size-quantization was investigated by reflectance UV spectroscopy. The functional groups were analyzed by the Fourier Transform Infrared Spectroscopy (FTIR) and elemental composition of the synthesized sample was determined by the EDX analysis.