R. Arun Kumar

Influence of calcination temperature on the luminescent properties of Eu3+ doped CaAl4O7 phosphor prepared by Pechini method

Motivated by the need for new phosphor for white light emitting diode (WLED) applications, CaAl₄O₇ phosphors activated by Eu(3+) rare earth ion was synthesized using the Pechini method at different calcination temperatures. The crystal structure and luminescent properties were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), UV-Vis diffuse reflectance spectroscopy (DRS), and photoluminescence spectroscopy (PL). The XRD and SEM patterns confirm the presence of a single grossite monoclinic phase (311) and the particles exhibit good crystallinity and the particle size varies with calcination temperature. Absorption peak of FT-IR shows the decomposition of citrate ethylene glycol complex and the formation of CaAl₄O₇:Eu(3+) phosphor. Diffuse reflectance spectra indicate an absorption in the UV-region. The photoluminescence excitation spectrum exhibited a broad band covering from 340 to 420 nm with a sharp band at 395 nm. CaAl₄O₇:Eu(3+) phosphor excited by near UV (395 nm) light showed a strong red emission at 611 nm. The emission band is due to f-f transitions within the 4f(6) configuration of Eu(3+) ions, respectively. The photoluminescence properties were found to be strongly dependent on the calcination temperature and the PL properties are superior for sample calcined at 950 °C.

Growth and characterization of L-threonine doped thiourea single crystals: an optical material

Single crystals of pure and L-threonine-doped thiourea, an organic nonlinear optical (NLO) material, were grown by slow evaporation technique at room temperature. The structure of the grown crystals was confirmed by powder X-ray diffraction analysis and the crystals belong to the orthorhombic structure. The UV-vis-NIR study was performed to reveal the optical behaviour of the grown crystals. The UV cut-off wavelength for the pure, 1 and 3 mol% LT-doped thiourea crystals were found to be 295 nm. The bonding structure and molecular associations due to chemical reactions were analysed and also the functional groups present in the crystals were identified using FTIR spectrum. Kurtz–Perry powder technique employing Nd:YAG laser was utilised to find the second harmonic generation efficiency of the grown pure and doped crystals which are found to be comparable to that of KDP.

Growth, structural and optical characterization of a new nonlinear optical crystal--hippuric acid doped potassium di hydrogen phosphate.

Potassium di hydrogen phosphate (KDP) is an efficient nonlinear optical crystal employed in frequency conversion applications. 1mol% hippuric acid doped potassium di hydrogen phosphate (HAKDP) crystals with the dimensions 35×8×4 mm(3) were grown using the slow evaporation technique. The grown HAKDP crystal is iso-structural with pure KDP, but a variation in the crystallographic parameters was observed. The UV-VIS-NIR study suggests that the crystal is highly transparent in the region 340-1200 nm. The functional groups present in the grown crystal were observed in the FTIR analysis. The powder SHG test performed on the grown crystal revealed the NLO efficiency of the crystal has increased due to doping when compared with pure KDP crystal.

Growth and characterization of a novel nonlinear optical borate crystal--yttrium calcium borate (YCB).

A new nonlinear optical single crystal yttrium calcium borate Y2CaB10O19 (YCB) was grown for the first time from its melt. The starting materials were prepared by the solid-state reaction method. The melting point of the synthesized material was identified to be 967 °C. YCB crystal exhibits monoclinic crystal structure with the space group C2. The crystalline perfection of the grown YCB crystal was found to be good. From the UV-VIS-NIR studies, the lower cutoff wavelength of the crystal occurs below 200 nm. The functional groups of the grown crystal were assigned using the FTIR data. The second harmonic generation (SHG) of the YCB crystal was observed using a Nd:YAG laser with a fundamental wavelength of 1064 nm. The laser damage threshold value of the YCB crystal was found to be very high - 10.5 GW/cm(2).

Photosynthesis and Associated Aspects Under Abiotic Stresses Environment

Abiotic stresses are the prime reason of crop loss worldwide, reducing average yields for most of the major crop plants by more than 50%. Plants as sessile organisms are persistently exposed to changes in environmental conditions. When these changes are swift and extreme, plants generally perceive them as stresses. However stresses are not necessarily a problem for plants because they have evolved effective mechanisms to avoid or reduce the possible damages. The response to changes in environment can be rapid, depending on the type of stress, and can involve adaptation mechanisms, which allow them to survive the adverse conditions. Extreme environmental conditions, such as high and low temperatures, waterlogging and deficits, salinity, and carbon dioxide (CO2) and ozone (O3) concentrations at the leaf surface strongly affect plant growth and development. Such abiotic stresses adversely affect on physiological mechanisms associated with plant responses, adaptation, and tolerance to stresses in terms of photosynthetic mechanisms, such as CO2 diffusion through stomatal control, photosystem II repair, ribulose bisphosphate carboxylase/oxygenase (Rubisco) activity, and generation of reactive oxygen species (ROS), are susceptible to damage that causes great diminution in photosynthetic efficiency. Therefore, photosynthesis is one of the key processes to be affected by abiotic stresses, which results in decrease in CO2 diffusion to the chloroplast and metabolic constraints. Although several structural and functional components of the photosynthetic apparatus are responsive to abiotic stresses, photosystem II (PS II) and Rubisco act as the major stress sensors. In addition, it is essential to systematize current knowledge on the complex network of interactions and regulation of photosynthesis in plants exposed to abiotic stresses. In this chapter, we brought the update knowledge emphasizing on the regulation of photosynthesis and associated aspects that are affected by various abiotic stresses.

Growth and characterization of amino acids doped sodium acid phthalate single crystals

Single crystals of pure and 1 mol% of L-alanine (LA-C3H7NO2), L-histidine (LH-C6H9N3O2) and L-arginine (LAR-C6H14N4O2)-doped sodium acid phthalate, C8H5NaO4 (SAP) were grown by slow evaporation solution growth technique at ambient temperature. Powder X-ray diffraction revealed that all the crystals possess orthorhombic crystal structure and revealed lattice distortion due to doping. Fourier transform infrared analysis confirmed the presence of various functional groups of SAP and amino acids in the grown crystals. Both pure and amino acids-doped crystals exhibited wide transmission range lying between 403 and 1100 nm, and the nature of transmittance of doped crystals are superior to that of pure crystals. The band gap energy values of the grown crystals were calculated. The effect of amino acid dopants on thermal and mechanical properties of SAP single crystals have also been studied and discussed in this paper. The second harmonic generation efficiency of the grown crystals was also studied.

Structural, spectroscopic, and nonlinear optical investigations on a novel nonlinear optical crystal: hippuric acid doped ammonium di hydrogen phosphate (HAADP).

Transparent single crystals of pure and 1 mol% hippuric acid doped ammonium di hydrogen phosphate (HAADP) were grown from aqueous solution by employing slow evaporation technique. Crystallinity of the grown crystals was studied by powder X-ray diffraction analysis. Both pure ADP and HAADP crystals exhibit tetragonal crystal structure. The bonding structure and molecular associations due to chemical reactions were analyzed by FTIR spectroscopy. It also confirms the functional groups present in the grown crystals. UV-Vis-NIR spectral analysis was carried out to study the optical characteristics of the crystals which reveal that the cutoff wavelength for both pure and hippuric acid doped ADP crystal is around 300 nm. From these spectra it can be clearly inferred that there is an absence of characteristic absorption in the region between 340 and 1200 nm, which is a most desirable property of a material for both SHG and other NLO applications. Second harmonic generation (SHG) test adopting the Kurtz Perry technique revealed that the second harmonic generation efficiency of HAADP is 1.5 times that of pure ADP crystal.