N. Rajmuhon Singh

Luminescence, lifetime, and quantum yield studies of redispersible Eu3+-doped GdPO4 crystalline nanoneedles: Core-shell and concentration effects

Crystalline nanoneedles of Eu3+-doped GdPO4 and Eu3+-doped GdPO4 covered with GdPO4 shell (core shell) have been prepared at relatively low temperature of 150 °C in ethylene glycol medium. From luminescence study, asymmetric ratio of Eu3+ emission at 612 nm (electric dipole transition) to 592 nm (magnetic dipole transition) is found to be less than one. Maximum luminescence was observed from the nanoparticles with Eu3+ concentration of 5 at. %. For a fixed concentration of Eu3+ doping, there is an improvement in emission intensity for core-shell nanoparticles compared to that for core. This has been attributed to effective removal of surface inhomogeneities around Eu3+ ions present on the surface of core as well as the passivation of inevitable surface states, defects or capping ligand (ethylene glycol) of core nanoparticles by bonding to the shell. Lifetime for D50 level of Eu3+ was found to increase three times for core-shell nanoparticles compared to that for core confirming the more Eu3+ ions with sym...

Synthesis and luminescence properties of CaMO4:Dy3+ (M = W, Mo) nanoparticles prepared via an ethylene glycol route

CaWO4 and CaMoO4 doped with Dy3+ nanoparticles are obtained via an ethylene glycol route at temperature as low as 130 °C. The XRD results reveal that all the doped samples are well assigned to the scheelite structure of the CaWO4 and the CaMoO4 phase. Upon excitation by ultraviolet radiation, the CaWO4:Dy3+ and CaMoO4:Dy3+ phosphors demonstrate the characteristic 4F9/2–6H13/2–15/2 emission line of Dy3+. Photoluminescence examination revealed yellow phosphorescence for CaWO4:Dy3+ and yellowish white for CaMoO4:Dy3+ nanoparticles. The highest emission is observed when doped with 5 at% Dy3+ for the CaWO4 host and 7 at% Dy3+ for CaMoO4 samples. Doping the host with Dy3+ tunes the emission wavelength from blue-green to white for CaMoO4 and blue to yellow for CaWO4 nanoparticles. This multicolour tuning emission could increase their applicability in fluorescent lamps and display panels.

Synthesis of CaWO4:Eu3+ phosphor powders via ethylene glycol route and its optical properties

Abstract Eu 3+ doped CaWO4 with tetragonal system were prepared at comparatively low temperature (125 °C) in ethylene glycol medium. The phosphor was further investigated by X-ray diffractometer (XRD), photoluminescence spectrophotometer (PL), Fourier transform infra red (FT-IR) spectroscopy and transmission electron microscopy (TEM). XRD analysis indicated a decrease in the unit cell volume of CaWO 4 with increasing Eu 3+ ion concentration. It indicated the homogeneous substitution of Ca 2+ ions in CaWO 4 by the Eu 3+ ions. TEM images showed that the particle size ranged from 20 to 200 nm and it could extend the application of the nanoparticles. The photoluminescence study showed that the intensity of electric dipole transition ( 5 D 0 → 7 F 2 ) at 614 nm dominated over the magnetic dipole transition ( 5 D 0 → 7 F 1 ) at 592 nm. The optimum concentration of Eu 3+ for the highest luminescence was found to be 20 at.%. The as prepared samples were found to be dispersible in water and methanol.

Spectral study of the complexation of Nd(III) with glutathione reduced (GSH) in the presence and absence of Zn(II) in aquated organic solvents

Studies on the difference in energy parameters and comparative absorption spectrophotometry involving 4f-4f transitions on Nd(III) and glutathione reduced (GSH) in the absence and presence of Zn(II) have been carried out in aquated organic solvents (50 : 50) like methanol, dioxane, acetonitrile and dimethylformamide. Variations in the spectral energy parameters — Slater-Condon (Fk) factor, Lande spin-orbit coupling constant (ξ4f), nephelauxetic ratio (β), bonding parameter (b1/2) and percent covalency (δ) — are calculated and correlated with binding of Nd(III) with GSH in presence and absence of Zn(II).

Absorption spectral analysis of 4f-4f transitions for the complexation of Pr(III) and Nd(III) with thiosemicarbazide in absence and presence of Zn(II) in aqueous and organic solvents.

The complexation of thiosemicarbazide with Pr(III) and Nd(III) in absence and presence of Zn(II), a soft metal ion in aqueous and organic solvents like CH(3)OH,CH(3)CN, dioxane (C(4)H(8)O(2)) and DMF (C(3)H(7)NO) and their equimolar mixtures are discussed by employing absorption difference and comparative absorption spectrophotometry. Complexation of thiosemicarbazide with Pr(III) and Nd(III) is indicated by the changes in the absorption intensity following the subsequent changes in the oscillator strength of different 4f-4f bands and Judd-Ofelt intensity (T(λ)) parameters. The other spectral parameters like energy interaction parameters namely Slater-Condon (F(k)), Racah (E(k)), Lande (ξ(4f)), Nephelauxetic ratio (β) and bonding parameters (b(1/2)) are further computed to explain the nature of complexation. The difference in the energy parameters with respect to donor atoms and solvents reveal that the chemical environment around the lanthanide ions has great impact on f-f transition and any change in the environment result in modification of the spectra. Various solvents and their equimolar mixtures are also used to discuss the participation of solvents in the complexation.

Diversity and Density of Aquatic Insects in the Lower Reach of River Moirang, Manipur, North East India

A study on the diversity and density of aquatic insects in the lower reach of river Moirang, Manipur, India was conducted using aquatic insects as bio indicator to ascertain the pollution status of the river as it discharges into the Loktak lake (Ramsar site), the lifeline of people of Manipur. The study revealed the presence of three orders, nine families, twelve genera and eighteen species of aquatic insects in the lower reach of the river. The orders were Hemiptera, Odonata and Coleoptera. There was total absence of sensitive groups of aquatic insects like Ephemeroptera, Plecoptera and Trichoptera. According to Engelmann’s scale, Diplonychus rusticus (Fabricius) was found eudominant followed by five subdominant and six recedent species. No species was found in the dominant range. Species diversity and evenness indices fluctuated throughout the year and Shannon H′<1 in all the months indicated a stressed and disturbed environment. This is confirmed by the record of low dissolved oxygen (DO), high biological oxygen demand (BOD) and high phosphate in the water of the river. Among the heavy metals, the ranges of both lead and mercury were found to exceed the WHO maximum permissible limit. Significant positive correlation of rainfall with pH, DO, BOD, nitrate, phosphate, Berger Parker dominance index (d) and significant negative correlation with diversity index (Shannon H′) indicated that rainfall is one of the important parameters in the ecology of the system. Canonical correspondence analysis (CCA) revealed that the important physico-chemical attributes of the ecosystem were air temperature, water temperature, depth, rainfall, BOD, DO, salinity, sodium, total alkalinity, iron and lead.

Studies on the complexation of neodymium(III) ion with 1,2,4-1H-triazole and 1,2,3-benzotriazole in absence and presence of calcium(II) ion in aqueous and some selected different aquated organic solvents by an absorption spectroscopy involving 4f–4f transitions

The absorption spectra of trivalent neodymium ion with 1,2,4-1H-triazole and 1,2,3-benzotriazole in absence and presence of calcium(II) ion in aqueous and some selected different aquated organic solvents have been recorded in the visible and near infrared regions. From the data available in the absorption spectra, various spectroscopic parameters such as Slator-Condon (F(k)), Lande spin-orbit coupling constant (ξ(4f)), nephelauxetic ratio (β), bonding parameter (b(1/2)), percent covalency (δ), oscillator strength (P) and Judd-Ofelt intensity (T(λ)) parameters have been evaluated. The Judd-Ofelt intensity, T(λ) (λ=2, 4, 6) parameters are utilized in evaluating the P(cal) from various excited states of trivalent neodymium ions and ratifying as an inner sphere complexations.

Solvent induced shape change in CePO4：Dy3＋ nanophosphors and effect of metal ions： A photoluminescence study

The influence of different solvents and metal ions (Li+, Ba2+, Bi3+) on the crystallization behaviour, morphology and enhancement in photoluminescence intensity of Dy3+ doped CePO4 were investigated. Highly crystalline luminescent nanophosphors of CePO4:Dy3+ re-dispersible in polar solvents were successfully prepared via a simple polyol route at 140 °C. As-prepared Dy3+ doped CePO4 nanophosphors prepared in EG and DMF appeared to have crystalline monoclinic phase but exhibited hexagonal phase when prepared in water and water mixed solvents. The hexagonal phase transformed to monoclinic phase after heating at 900 °C. TEM study revealed different shapes of the synthesized nanophosphors with change of solvents. The luminescence intensity of 4F9/2→6H15/2 at 478 nm (blue) was found to be more prominent than 4F9/2→6H13/2 at 572 nm (yellow). The introduction of metal ions (Li+, Ba2+ and Bi3+) in CePO4:Dy3+ led to considerable luminescent enhancement. The nanophosphors were subsequently incorporated in polymer films of PVA which showed the characteristic emissions of Dy3+. It also served as an effective method to improve the performance of polymer materials and brought about novel properties in them.

Computation of energy interaction parameters as well as electric dipole intensity parameters for the absorption spectral study of the interaction of Pr(III) with l-phenylalanine, l-glycine, l-alanine and l-aspartic acid in the presence and absence of Ca2+ in organic solvents

Studying the absorption difference and comparative absorption spectra of the interaction of Pr(III) and Nd(III) with l-phenylalanine, l-glycine, l-alanine and l-aspartic acid in the presence and absence of Ca(2+) in organic solvents, various energy interaction parameters like Slater-Condon (F(K)), Racah (E(k)), Lande factor (xi(4f)), nephelauxetic ratio (beta), bonding (b(1/2)), percentage-covalency (delta) have been evaluated applying partial and multiple regression analysis. The values of oscillator strength (P) and Judd-Ofelt electric dipole intensity parameter T(lambda) (lambda = 2, 4, 6) for different 4f-4f transitions have been computed. On analysis of the variation of the various energy interaction parameters as well as the changes in the oscillator strength (P) and T(lambda) values reveal the mode of binding with different ligands.

Evaluation of intensity and energy interaction parameters for the complexation of Pr(III) with selected nucleoside and nucleotide through absorption spectral studies

The interactions of Pr(III) with nucleosides and nucleotides have been studied in different organic solvents employing absorption difference and comparative absorption spectrophotometry. The magnitudes of the variations in both energy and intensity interaction parameters were used to explore the degree of outer and inner sphere co-ordination, incidence of covalency and the extent of metal 4f-orbital involvement in chemical bonding. Various electronic spectral parameters like Slater-Condon (F(k)), Racah (E(k)), Lande parameter (ξ(4f)), Nephelauxatic ratio (β), bonding (b(1/2)), percentage covalency (δ) and intensity parameters like oscillator strength (P) and Judd Ofelt electronic dipole intensity parameter (T(λ), λ=2,4,6) have been evaluated. The variation of these evaluated parameters were employed to interpret the nature of binding of Pr(III) with different ligands i.e. Adenosine/ATP in presence and absence of Ca(2+).