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Ultraviolet emitting Gd3+ doped phosphors have recently attracted significant attention from the optical science community owing to their important applications in the areas of photothermal therapy, transilluminators and sensitizer based photoluminescent phosphors (PLPs). It was found in several previous studies that the annealing temperature and water content has a profound influence on the emission intensity and luminescence lifetime of PLPs. In this context, we have synthesized Th(C2O4)2·6H2O:Gd3+ (TOHG) and characterized it using photoluminescence (PL) and electron paramagnetic resonance (EPR) spectroscopy. Emission spectroscopy showed the presence of a singular peak at 311 nm due to an electric dipole transition, suggesting the extremely low symmetry around Gd3+ in TOHG. Luminescence lifetime measurements suggested two different local environments of Gd3+ in TOHG; the shorter lived one (S) is closer to oxygen vacancies and the longer lived one (L) is further away from the oxygen vacancies. The time resolved emission spectrum shows a slightly different peak profile for S and L. The EPR spectra of TOHG suggested that Gd3+ is situated in a nearly eight-fold coordination of oxygen (cubic coordination) at the Th4+ ion. Furthermore, we carried out thermal treatment of TOHG at 250 °C which led to Th(C2O4)2·2H2O:Gd3+(TODG) which on further annealing at 300 °C was converted into anhydrous thorium oxalate (TOAG). X-ray diffraction analysis suggested a triclinic lattice structure for TOHG and a monoclinic and orientationally disordered structure for TOAG. The PL emission intensity and excited state lifetime were found to be greater for TOAG due to the absence of the non-radiative transition provided by water molecules. The EPR spectra of TOAG suggested lowering of the site symmetry to rhombic symmetry in TOAG. This is in agreement with our structural analysis. Such a complete spectrum of work wherein the structure, excited state dynamics and spin properties of Gd3+ were investigated will open up a new avenue into gadolinium photophysics, particularly for researchers to explore actinide oxalate with a view to thermally tuning its properties. [ABSTRACT FROM AUTHOR]

This work highlights the role of defects, excitation energy, and energy transfer in realizing color-tunable Green → Red → White from a single phosphor. In this work, thorium-based K2Th(PO4)2:Eu3+ (KTPE) phosphor was explored for the first time. Rietveld refinement of the powder XRD data showed the formation of a phase pure compound and a reduction in the lattice parameters upon europium doping. Undoped K2Th(PO4)2 (KTP) depicted bright green emission under UV irradiation due to the presence of oxygen vacancies (OVs) in the lattice. Further upon host excitation with 250 nm, complete host-to-Eu3+ energy transfer occurred to produce red emission due to 5D0 → 7F2 transition of europium ions with high asymmetry and a branching ratio with an internal quantum yield (IQY) of 53%. On the other hand, under europium excitation with 395 nm, emission spectra displayed host as well as europium emission, producing near white emission with an IQY of 49%. There were slightly more non-radiative channels under dopant excitation compared to the host. Evaluation of the color coordinates and correlated color temperature suggested that the white light was neutral with perfect amalgamation of red, green, and blue. Lifetime spectroscopy suggested a monoexponential decay behavior owing to the stabilization of Eu3+ at Th4+ ion, leading to the formation of oxygen vacancies and antisite defects. These defects together with the size and charge mismatch produce substantial lattice strain in the KTPE. Such lattice strain combined with the host crystalline field leads to substantial Stark splitting, in turn to a reduction in the symmetry of KTPE. This work gives a complete flavor of structure–property correlation in designing a new color tunable phosphor by controlling defects, excitation energy, and host-to-dopant energy transfer in the complex phosphate host consisting of alkali and actinide ions. [ABSTRACT FROM AUTHOR]

Zirconium phosphosilicate (ZPS) has been prepared by gelation route for its ion exchange applications. ZPS was characterised by X-ray diffraction technique (XRD), thermogravimetry (TG), scanning electron microscopy (SEM), Fourier transformed Infrared Spectrometry (FTIR) and surface area analysis. K+ ion exchange behaviour was studied by pH titration. The material was found to extract Pu selectively over U from different mineral acids. Pu sorption behaviour on ZPS packed column was also been carried out. The pore volume was evaluated as 0.1336 mL g−1. The FTIR revealed the presence of –OH and PO43− groups on the surface of the material, while the SEM image indicates the irregular morphology and size of the sorbent. Different isotherm model: Langmuir, Freundlich, Dubinin–Rodushkevich and Temkin were used to understand the nature of sorption, while Lagergren 1st order, Intraparticle diffusion and pseudo 2nd order kinetics were used for modelling sorption kinetics. Suitable elution method was used for quantitative stripping of plutonium from sorbent. The radiolytic stability of the sorbent was evaluated upto 1500 kGy. A comparative evaluation of the sorption process has also been carried out with that reported in literature. [ABSTRACT FROM AUTHOR]

The present phosphor K2Ca(SO4)2, doped by dysprosium and europium, is synthesized by the solid-state diffusion method. The doping concentration varied from 0.1 to 0.5 mol% by weight. A phosphor is studied for X-ray powder diffraction, surface morphology analytical scanning electron microscopy and analyzed by energy-dispersive X-ray spectroscopy. The prepared phosphor K2Ca(SO4)2, doped by Dy and Eu, has been characterized for thermoluminescence (TL) glow curve, showing maximum peak temperatures at 176°C and at 200°C, respectively. TL peak intensity of K2Ca(SO4)2: Dy and Eu was compared with the standard TLD CaSO4:Dy phosphor. Both phosphors show the dose linearity ranging from 20 to 240 Gy doses of γ-rays of 60Co source at room temperature. Negligible fading has been observed when irradiated with γ-rays and stored for 60 days without taking any care from sunlight. The TL materials were used in powder forms. The linearity of ESR response with dose for powder forms of K2Ca(SO4)2: Dy was also studied using the signals at g = 2:0039 (SO3−) and at g = 2:02282 (SO4−). It was observed that the range of linearity of dose response extended between 20 and 240 Gy. Kinetic parameters have been calculated using three different methods: Chen's peak shape method, various heating rate method and initial rise method. To study the heating rate method, the glow curve was recorded for the heating rate as 1°C, 3°C, 5°C, 7°C, 9°C each time. Electron spin resonance (ESR) shows the ionic radical formation during γ-irradiation, which is responsible for TL. The effect of temperature and microwave power on the ESR signal was also studied. [ABSTRACT FROM AUTHOR]

LiAl5O8 doped with varying concentrations of Eu were synthesized by a solid state reaction route. Phase purity of the prepared phosphors was determined using X-ray diffraction technique. Dynamic light scattering technique was used to estimate the average particle size of the synthesized products that was found to be ~ 110 nm. The doped phosphor samples exhibited strong excitation band in the range 210-290 nm with 613 nm emission suggesting the stabilisation of trivalent Eu. With 394 nm (UV) excitation, strong visible luminescence was observed at 613 nm corresponding to the 5D0 → 7F2 transition of the Eu3+ ions. The emission parameters were optimised by varying the dopant ion concentration and annealing temperature. The intensity parameters (Ωλ, λ = 2, 4 and 6), radiative transition probabilities (AR), radiative lifetime (τR) and branching ratios (β) for the system were evaluated in the framework of the model given by Judd-Ofelt. The CIE coordinates for the system were evaluated by adopting standard procedure, which suggested that the system has enough potential to be used as a red phosphor. [ABSTRACT FROM AUTHOR]

The present paper reports on the γ-ray and C6+ ion beam induced effect on the structural and luminescence properties of Eu doped LiNaSO4 phosphors synthesized via wet the chemical method. The material was irradiated by 60Co and 137Cs γ-rays and 75 MeV C6+ ions in a fluence range varying from 2 × 1010 to 1 × 1012 ion per cm2. The ion induced modified properties were investigated using X-ray diffraction (XRD), micro-Raman spectroscopy, photoluminescence (PL), thermoluminescence (TL) and electron paramagnetic resonance (EPR) studies. The XRD and micro-Raman results confirm the loss of crystallinity and elongation of the lattice parameters after ion beam irradiation. The presence of both divalent as well as trivalent states of Eu ions at multiple sites of LiNaSO4 is observed by PL study. Irradiation of the LiNaSO4:Eu phosphor with a C6+ ion beam modifies the population of the valence state of the doped rare earth Eu ion and enhances the TL sensitivity of this phosphor. The nature of the prominent TL glow curve is identical for both γ-ray and C6+ ion beam irradiated materials while additional deep trap levels appear in the latter due to the formation of several types of cation and anion vacancy. The electron paramagnetic resonance (EPR) technique also supports the presence of the Eu ion at multiple sites and provides information regarding several types of radical produced after γ-ray and C6+ ion irradiation. Finally, a mechanism is presented for the thermally stimulated luminescence phenomenon on the basis of our observed results from the PL, TL and EPR studies. The reason behind ion beam irradiation induced modification of the TL properties and enhancement of luminescence intensity is also explained in this report. [ABSTRACT FROM AUTHOR]

This study reports the synthesis of nanocrystalline undoped and europium doped BaWO4:Eu3+ nanophosphors by a mechanical activation process using high energy ball mill (HEBM) technique. The prepared nanophosphors were characterized systematically by Rietveld analysis of the X-ray powder diffraction (XRD) data, Raman spectroscopy, energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The synthesized nanophosphors were found to possess spherical morphology and small particle sizes ∼25 nm. To explore this material for application in luminescence, detailed time resolved photoluminescence studies were carried out. It was observed that it is a rare breed of phosphor material that exhibits exceptional luminescence properties such as the capability to give high emission output till 5.0 mol% without undergoing quenching and unique property to get excited by mid ultraviolet (MUV) light, near ultraviolet (NUV) light, as well as by visible light such as blue and green. It was also observed that energy transfer primarily takes place from tungstate group of host to Eu3+. In fact energy transfer from the host to Eu3+ becomes more and more efficient with the increasing concentration of Eu3+ ions. Two lifetime values are observed for all europium ion (Eu3+) concentrations, one of the order of 465–650 μs (TS, short lifetime) and the other of the order of 1050–1320 ms (TL, longer lifetime). This reflects the fact that Eu3+ ions occupy two sites; regular symmetric Ba2+ site (S1) and asymmetric site (S2), which will be closer to charge compensating defects. Calculation of Judd–Ofelt parameter illustrated that at all europium concentrations, the local surrounding around it lacked inversion symmetry (asymmetric environment), and the exact point group symmetry around europium ion was found to be C6v. The red purity (intense 5D0–7F2) and high quantum efficiency (78%) of BaWO4:Eu3+ projects it as a new red phosphor for application in white light emitting diodes. [ABSTRACT FROM AUTHOR]

The speciation of a particular element in any given matrix is a prerequisite to understanding its solubility and leaching properties. In this context, speciation of uranium in lanthanum zirconate pyrochlore (La2Zr2O7 = LZO), prepared by a low-temperature combustion route, was carried out using a simple photoluminescence lifetime technique. The LZO matrix is considered to be a potential ceramic host for fixing nuclear and actinide waste products generated during the nuclear fuel cycle. Special emphasis has been given to understanding the dynamics of the uranium species in the host as a function of annealing temperature and concentration. It was found that, in the LZO host, uranium is stabilized as the commonly encountered uranyl species (UO22+) up to a heat treatment of 500 °C at the surface. Above 500 °C, the uranyl ion is diffused into the matrix as the more symmetric octahedral uranate species (UO66-). The uranate ions thus formed replace the six-coordinated 'Zr' atoms at regular lattice positions. Further, it was observed that concentration quenching takes place beyond 5 mol% of uranium doping. The mechanism of the quenching was found to be a multipolar interaction. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]