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An analytical method was developed based on the D.C. arc carrier distillation atomic emission spectrometric (D.C. Arc AES) technique for determination of trace metallic impurities (Al, Ca, Co, Cr, Cu, Fe, Mg, Mn, Mo, Na, Ni, Si, Sn, Ti, V and Zn) in uranium silicide samples. Chemical quality control was also carried out for the precursor materials in order to track the source of impurities in the final fuel materials. The method was validated using synthetic samples. To minimize the spectral interference, a suitable carrier (5% AgCl) was used to sweep away the trace constituents into the arc preferentially, leaving the major matrix as a refractory material. The use of a charge coupled device (CCD) detector was found to improve the overall analytical performance in terms of detection limits, precision, linear dynamic range and most importantly providing an opportunity to choose additional analytical lines, which is highly desirable, especially for trace level determination of analytes in an emission-rich matrix. The energy dispersive X-ray fluorescence (EDXRF) spectroscopic technique was employed each time for comparative evaluation of the precursors and the product.

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.

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.

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 PO4 3− 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.

Plutonium in the form of oxide is stored in plastic vials and bottles during its analysis for trace metal assay. Due to radiation damage and moisture, small amount of oxide samples were found to be adhering to surface of vials/bottles. This required methods for safe disposal. Methods involving wet chemical and dry cleaning procedures were evaluated for effective removal of sticking α active plutonium oxide powder from these vials for their safe disposal. Dry cleaning method for removal of plutonium activity was found to be effective method for disposal of storage vial, while wet chemical method was found to be more suitable for removal of plutonium from damaged PVC bottles. The recovered Pu was checked for chemical purity for 24 analytes using glove box adopted high resolution inductively coupled plasma atomic emission spectrometry.

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 ...

Designing new materials for solid state lighting and understanding the various intricacies involved for designing them such as defects, energy transfer and concentration quenching is very important. Such materials will be highly beneficial in optoelectronics, energy and health industry. In this work, an effort has been taken in that direction by exploring room temperature synthesized Dy3+ doped β-Ag2MoO4 using simple co-precipitation method under neutral conditions. Pure β-Ag2MoO4 showed blue – green emission upon shining with UV light. On doping Dy3+an efficient host-dopant energy transfer takes place. The concentration quenching study revealed non-radiative energy transfer in Dy3+ doped β-Ag2MoO4 takes place via Dexter mechanism of exchange interaction. Additionally, on doping Dy3+ ions in the β-Ag2MoO4 a multicolour emission could be observed due to presence of blue, yellow and red bands induced by host sensitized energy transfer. Positron lifetime studies show that the Dy3+ doping creates cation vacancies. Positron lifetimes and asymmetry ratios in PL emission show that Dy3+stabilizes at Ag+ sites. Photoluminescence Lifetime Spectroscopy revealed non-homogenous distribution of Dy3+ ions and its surroundings differ in terms of their vicinity with respect to defects created due to aliovalent doping. Such complete spectrum of work on concentration quenching study, UV excited photoluminescence, defect spectroscopy, local structure of dopant ion and excited state lifetime indicate that the developed phosphor may potentially be used for solid state phosphor for LED application. Future work will be seeing how the material properties change in going to nanodomain and to make it excitable using f-f band (351 nm). The only demerit of this phosphor is the poor absorption in this region.

LiMgBO3 :Dy3+ , a low Zeff material was prepared using the solution combustion method and its luminescence properties were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermoluminescence (TL), photoluminescence (PL), Fourier transform infrared spectroscopy, and electron paramagnetic resonance (EPR) techniques. Reitvield refinement was also performed for the structural studies. The PL emission spectra for LiMgBO3 :Dy3+ consisted of two peaks at 478 due to the 4 F9/2 →6 H15/2 magnetic dipole transition and at 572 nm due to the hypersensitive 4 F9/2 →6 H13/2 electric dipole transition of Dy3+ , respectively. A TL study was carried out for both the γ-ray-irradiated sample and the C5+ irradiated samples and was found to show high sensitivity for both. Moreover the γ-ray-irradiated LiMgBO3 :Dy3+ sample showed linearity in the dose range 10 Gy to 1 kGy and C5+ -irradiated samples show linearity in the fluence range 2 × 1010 to 1 × 1011 ions/cm2 . In the present study, the initial rise method, various heating rate method, the whole glow curve method, glow curve convolution deconvolution function, and Chen's peak shape method were used to calculate kinetic parameters to understand the TL glow curve mechanism in detail. Finally, an EPR study was performed to examine the radicals responsible for the TL process.

This work discusses about synthesis of relatively unexplored carnegieite type NaAlSiO4 and designing it as efficient europium ion doped red phosphor. The synthesized powder has been systematically characterized using powder X-ray diffraction (XRD), Raman spectroscopy, Thermogravimetry - Differential Thermal Analysis (TG-DTA) and photoluminescence (PL) techniques. The effects of Eu3+ concentration on the photoluminescence properties were investigated. Concentration dependent emission spectroscopic studies suggested quenching at 0.5% doping level due to multipolar interaction. Stark splitting analyses revealed that the point group around Na+ ions decreases with Eu3+ doping and it is found to be C4v in Eu3+ doped NaAlSiO4. The asymmetry ratio was found to increase monotonically with europium concentration due to increasing density of sodium ion vacancies (VNa) which further distort the structure of NaAlSiO4. Lifetime spectroscopic studies suggested stabilization of europium ion at sodium site in two different environment; one nearer to charge compensating defect and one at far off distance. Judd-Ofelt analysis suggested asymmetric and highly polarizable environment around europium ion lead to enhanced red emission. The structure-property correlations indicate the potential of such structures for enhanced luminescence, scintillation and other optoelectronic properties.

COVID-19 is the world’s first digital pandemic. Digital tools and technologies have been developed to track and trace the spread of the virus, screen for infection, and the pandemic has accelerated the use of digital technology in the delivery of healthcare. The continued development of these tools and technologies, the monitoring of the virus and the development of new tests, treatments and vaccines are dependent on the collection of and access to vast amounts of personal data. This includes clinical data, epidemiological data and public health data that may be collected from laboratories, medical records, wearables and smartphone apps. Previous public health emergencies (PHEs) have demonstrated the importance in making this data available, and early in the COVID-19 pandemic, there were calls for making all kinds of data, including clinical trial data, routine surveillance data, genetic sequencing, and data on the ongoing monitoring of disease control programmes, openly and rapidly available. As part of this, personal data on age, race, sex, health, ethnic group, and socioeconomic factors have been shared. This has helped led to the rapid development of COVID-19 interventions. It has also enabled the better understanding of factors contributing to difference in infection rates and effectiveness of tests, treatments, and vaccines. However, the use of this particularly sensitive data can infringe upon individual and group privacy, increase the risks of individual and group stigma and discrimination, and it may negatively impact already vulnerable, marginalised or minority populations. [...]

CaMg2(SO4)3 host and CaMg2(SO4)3:Dy3+ phosphor (where Dy3+ = 0.05, 0.1,0.2, 0.5 and 1 mol%) were synthesized via solid state synthesis method at 700 °C. Phase formation of the compound was confirmed by obtaining its X-ray diffraction (XRD) pattern and the surface morphology was analyzed with the scanning electron microscopy (SEM) technique. Photoluminescence (PL) excitation and emission spectra of CaMg2(SO4)3:Dy3+ phosphor shows characteristic emission and excitation peaks of Dy3+ ions, which confirms the doping of Dy3+ ions in the host. Material was irradiated with γ-rays and C6+ ion beam. Thermoluminescence (TL) glow curve of irradiated material was recorded at the heating rate of 5 °C s−1. A single TL peak is obtained after γ-rays irradiation for CaMg2(SO4)3 host at 158 °C and two TL peaks were seen for CaMg2(SO4)3:Dy3+ at 129 °C and 355 °C. With increase in Dy3+ concentration, TL intensity is increased but the nature of TL glow curve remained same. Material was quenched from 400 °C and its TL was recorded by irradiating it with γ-rays and C6+ ion beam (75 MeV). TL intensity of quenched CaMg2(SO4)3:Dy3+ compound enhanced significantly as compared to annealed CaMg2(SO4)3:Dy3+ compound. Electron paramagnetic resonance (EPR) study was carried out on irradiated (γ-ray and C6+ beam) CaMg2(SO4)3:Dy3+ compound to analyse radicles formed in the irradiation process and possible mechanism of TL. Correlated study of TL, PL and EPR is done.

Local structure analysis of dopant ion, understanding host to dopant energy transfer dynamics and defects characterization in a doped material which plays an important role in the designing a highly efficient opto-electronic material. In this connection a new Sm3+ doped Gd2Zr2O7 pyrochlore material was synthesized using gel-combustion technique and was characterized systematically using X-ray diffraction (XRD), time resolved photoluminescence spectroscopy (TRPLS), positron annihilation lifetime spectroscopy (PALS) and density functional theory (DFT) based ab-initio calculation. Based on DFT site selective energetics calculation and luminescence decay measurement, it was observed that the Sm3+ was distributed at both Gd3+ and Zr4+ site with higher Sm3+ fraction at the Gd3+ site. PALS was used to probe the presence of defects in the phosphor. In this work intense orange-red emission is realized through manipulating the energy transfer from host defect emission (oxygen vacancies) to Sm3+ which allows color emission from green in undoped to orange-red in doped samples. Effect of dopant concentration and annealing temperature was probed using TRPLS and PALS. These all information is highly important for researcher looking to achieve pyrochlore based phosphor materials with high quantum yield.

An effort was taken to carry our speciation study of uranium ion in technologically important cerate host Sr2CeO4 using time resolved photoluminescence spectroscopy. Such studies are not relevant only to nuclear industry but can give rich insight into fundamentals of 5f electron chemistry in solid state systems. In this work both undoped and varied amount of uranium doped Sr2CeO4 compound is synthesized using complex polymerization method and is characterized systematically using X-ray diffraction (XRD), Raman spectroscopy, impedance spectroscopy and scanning electron microscopy (SEM). Both XRD and Raman spectroscopy confirmed the formation of pure Sr2CeO4 which has tendency to decompose peritectically to SrCeO3 and SrO at higher temperature. Uranium doping is confirmed by XRD. Uranium exhibits a rich chemistry owing to its variable oxidation state from +3 to +6. Each of them exhibits distinct luminescence properties either due to f-f transitions or ligand to metal charge transfer (LMCT). We have taken Sr2CeO4 as a model host lattice to understand the photophysical characteristics of uranium ion in it. Emission spectroscopy revealed the stabilization of uranium as U (VI) in the form of UO66- (octahedral uranate) in Sr2CeO4. Emission kinetics study reflects that uranate ions are not homogeneously distributed in Sr2CeO4 and it has two different environments due to its stabilization at both Sr2+ as well as Ce4+ site. The lifetime population analysis interestingly pinpointed that majority of uranate ion resided at Ce4+ site. The critical energy-transfer distance between the uranate ion was determined based on which the concentration quenching mechanism was attributed to electric multipolar interaction. These studies are very important in designing Sr2CeO4 based optoelectronic material as well exploring it for actinides studies.

In order to evaluate the trap level spectroscopic properties of Uranium in ZnAl2O4 spinel host, undoped and Uranium doped ZnAl2O4 samples were synthesized. From photoluminescence (PL) data it was confirmed that uranium gets stabilized in the system as UO66− (octahedral uranate). Electron spin resonance (ESR) studies for the gamma irradiated sample suggested the formation of O2−, F+ and V centres. From the TSL (thermally stimulated luminescence) data, the trap parameters such as frequency factor and activation energy etc. were evaluated. From ESR-TSL correlation it was confirmed that the destruction of O2− ion coincides with TSL glow peak appeared at 332 K.

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.

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.

To resolve the issue of aggregation induced quenching (AIQ), poor adhesion/dispersion on film and fiber, limited dispersability/solubility and non biocompatibility issue; phosphor powder particles are generally casted into solution form. It was found in most cases that lanthanide luminescence and lifetime reduced substantially in aqueous medium and ionic liquid. Deep eutectic solvent (DES) has been found to be an alternate and more efficient solvent for lanthanide luminescence. With similar intention we have synthesized europium type (IV) DES (EuDES) via mechanochemical synthesis employing europium nitrate and urea. Fourier transformed infrared spectroscopy (FTIR) studies confirms that in DES, the Eu3+ ion is surrounded by bidentate nitrate ions and urea is coordinated to europium centre by C O group. There is no water molecule in primary coordination sphere of Eu3+ ion. Interestingly with rigid H-bonding and strong chemical interaction offered by DES; Eu3+ CTB is quenched whereas very high intensity of Eu3+ intra f-f transition appears which was reversal from usual trend. Moreover asymmetry ratio was found to be more than 3 with predominantly high intensity of electric dipole transition (EDT) suggesting very asymmetric environment around Eu3+ in DES. But the distribution of europium was found to be very homogenous with luminescence lifetime of ~3.7 ms and point group symmetry ~ C6v. Judd-Ofelt analysis suggested very low non-radiative channels present in DES resulting in extremely high quantum yield ~76% and very high color purity of 94.72% which was also assisted by absence of any water molecule as suggested by FTIR measurement.

Nanocrystalline (n-SWO) and microcrystalline (b-SWO) samples of SrWO4 were prepared using polyol and solid state diffusion method, respectively and their crystallite sizes were estimated by powder X-ray diffraction employing Williamson-Hall method. Morphostructural characterization using transmission electron microscopy (TEM) revealed the increased thermal agglomeration and size enhancement in b-SWO particles relative to n-SWO. The photoluminescence emission in both the samples was broad in the range of 400–650 nm. The emission consisted mainly of a narrow peak in the blue region and a broader emission in green region. The fraction of emission in the green region was higher for nanocrystalline SrWO4 than its microcrystalline counterpart. The higher intensity of green emission in nanocrystalline sample is attributed to the large concentration of the oxygen related vacancies.

X-ray opacity of polymer based medical implants is a desirable attribute for implant placement and function monitoring. This study presents the development of flexible thermoplastic composites with high radiopacity, low mechanical hysteresis, and excellent mechanical integrity via modulating vinyl acetate (VA) content in the melt compounded ethylene vinyl acetate copolymer (EVA) and barium sulfate (BS) composites. Extensive rheological, mechanical hysteresis, morphological, X-ray diffraction, mass attenuation and thermo-mechanical analysis were carried out to understand the interplay between the morphological distribution BS particles in the composites and the VA content. The results showed that 0.7 mm thick sheet of EVA/BS composites had markedly higher gray value (radiopacity) than 1 mm sheet of aluminum while retaining more than 1200% elongation at break and complete flexibility. Time-temperature (t-T) superimposition studies, fractional free volume, radiopacity, crystallinity, mechanical hysteresis, phase imaging, structural breakdown, storage modulus, loss factor and the complex viscosity of the melt showed high dependence on the vinyl acetate content of EVA and on the BS loading. These results will enable designing of flexible and thin radiopaque polymer composites for X-ray imaging applications, with predetermined physicomechanical and radiopacity behavior.

Phase purity, optical properties and defects in new near white light emitting rare earth free Sr2V2O7:Bi3+phosphors were investigated. Emission spectrum of Sr2V2O7 displayed two peaks at all excitation wavelength approximately around 450 (P1) and 600nm (P2). With increase in the excitation wavelength; emission intensity increases and there is a red and blue shift in Peak P1 and P2, respectively. On bismuth doping, the two Peaks P1 and P2 slowly starts merging and become a single broad peak at 5% doping. Bismuth doping also reduces the emission peak energy. This is attributed to substitution of Bi3+ at Sr2+ site which would distort VO4 tetrahedra, thereby reducing the energy difference between the 3T and 1A levels of VO43− distorted tetrahedral. This dual role of bismuth doping and excitation energy leads to interesting tunability in white emission from cool to warm white. This opens a new arena in phosphor research because of great role of white LEDs (both warm and cool) in outdoor and indoor lighting. Keywords: White light, Pyrovanadate, Photoluminescence, Positron annihilation, Phosphors, Tunable

Ba 1−x Eu x MoO 4 phosphors were synthesized by complex polymerization method. The prepared phosphor material was extensively characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetry (TG) and differential thermal analysis (DTA). The introduction of europium upto 2 mol% doesn’t change the crystal structure. The influence of Eu concentration on the luminescent properties of phosphors was analyzed. It was seen that, under UV irradiation, the pure BaMoO 4 sample shows multicolor emission. The blue and green emission was attributed to 1 T 2 → 1 A 1 transition within MoO 4 2− moeity (shallow defects), whereas the red- orange emission to the defect MoO 3 group (deep defects). The intensity of magnetic dipole transition (MDT) was found to be lower than that of electric dipole transition (EDT) which indicates the low -⁠ symmetry acentric environment of Eu 3+ ions. Based on Stark splitting, the actual site symmetry of Eu 3+ in BaMoO 4 was clarified as C 6v ; reduced from actual S 4 for Ba 2+ ion in BaMoO 4 . The decay curve shows two different lifetime value 11.2 µs (τ 1 ) (host contribution) and 693 µs (τ 2 ) (europium sitting at Ba 2+ site) with magnitudes 14% and 86% respectively. The value of host dopant energy transfer efficiency calculated under forbidden f-f transition excitation was found to be lower at 12.6% as compared to 76% in case of excitation by allowed charge transfer band. To find out the concentration quenching mechanism, the critical energy-transfer distance for the Eu 3+ ions was evaluated to be 33.81 A, which was found to be greater than 10 A and signify electric multipolar interactions as the only mode of energy transfer The intensity of peaks corresponds to EDT was found to be high in comparison to the peak due to MDT in all the Eu- doped samples: indicating the asymmetric local site symmetry around Eu 3+ . This is also reflected in the JO (Judo Ofelt) parameter trend; at all concentrations, Ω 2 value is greater than Ω 4 indicating the high covalency of the Eu 3+ ligand bonding and asymmetric environment around europium ion in BaMoO 4 , which is highly probable because it occupies the asymmetric Ba 2+ position.

This study describes a comparative analysis of γ-ray irradiated thermoluminescence properties of Ce 3+ /Dy 3+ and Eu 2+ doped LiAlO 2 phosphor. LiAlO 2 : Ce 3+ /Dy 3+ /Eu 2+ phosphors were synthesized by solution combustion method. The as synthesized phosphors were characterized by X-ray diffraction (XRD) and Scanning electron microscopy (SEM) for structural and morphological study. Rietveld Refinement of XRD patterns were executed by using Fullprof suit software program. Thermoluminescence characteristics of these phosphors show a linear dose response for a wide range of gamma radiation, especially Eu 2+ doped LiAlO 2 phosphor. The presence of large number of lithium vacancies in LiAlO 2 phosphor was supposed to be responsible for TL characteristics. Electron paramagnetic resonance (EPR) study of un-doped and Ce 3+ /Dy 3+ /Eu 2+ doped LiAlO 2 phosphor was carried out to confirm the presence of Eu 2+ ion and cation, anion vacancies in the host lattice. The responsible defect recombination mechanism for observed TL peak in LiAlO 2 was developed on the basis of TL and EPR study of irradiated and un-irradiated samples. TL kinetics was studied through glow curve deconvolution, Chen's peak shape method and initial rise method. A good match of kinetic parameters was observed between Chen's peak shape method and IR method. The present phosphors may find application in the dosimetry of high dose ionizing radiation.

A procedure was developed for determination of Np using HR Sequential ICP-AES. Mutual interference and background free spectral lines of Np at 295.66, 297.43, 297.49, 302.64 nm were identified. The samples of higher concentration (10–20 µg/mL) of Np had been analyzed. Analytical values of 10–20 µg/mL samples were found to be in good agreement with the expected amounts. The concentration of Np between 2 and 4 μg/mL slightly affected as compared to higher concentration. In U/Pu, Np-295.66, 297.43 nm lines were monitored which showed noticeable enhancement of their intensities. The repetitive analyses showed that the precision was better than 2% RSD.

Nanocrystalline ThO2:Sm3+ was synthesized using wet-chemical route and characterized using X-ray diffraction (XRD), photoacoustic (PA) and photoluminescence (PL) spectroscopy. PA absorptions of Sm3+ doped samples are found to be quite weak as compared to Nd3+, while PL of Sm3+ was intense. As the energy gap between lowest luminescent levels and highest non-luminescent level in samarium ion is around 7000 cm−1; it is highly fluorescing compared to Nd3+ which has close by levels. Through photoacoustic data it was pointed out that large covalent character exists in ThO2:Nd3+ compared to ThO2:Sm3+.

ZnGa2O4 and Europium incorporated ZnGa2O4 powder samples were prepared by solid state reaction of ZnO, Ga2O3 and Eu2O3 in stoichiometric quantities at 900 °C. The samples were subjected to AC powder electroluminescence and photoluminescence studies. Undoped ZnGa2O4 showed an electroluminescence peak with emission maximum around 525 nm, characteristic of luminescent centers like GaO6 structural units, anti-site defects and oxygen vacancies present in the lattice. Unlike this, for Europium incorporated ZnGa2O4 samples, blue light emission, characteristic of Eu2+ ions has been observed upon application of AC voltages. Europium ions also exist as separate Eu3+ containing phase in the samples as confirmed by photoluminescence studies. Electron Paramagnetic Resonance (EPR) studies confirmed the incorporation of Eu2+ at six coordinated Zn2+ site (anti-site) in ZnGa2O4 lattice.

A systematic photoluminescence based investigation was carried out to understand the complexation of Eu 3 + with different ligands (TBP: tri-n-butyl phosphate, DHOA: di-n-hexyl octanamide, Cyanex 923: tri-n-alkyl phosphine oxide and Cyanex 272: Bis (2,4,4 trimethyl) pentyl phosphinic acid) used for preferential separation of lanthanides and actinides in various stages of nuclear fuel cycle. In case of TBP and DHOA complexes, 3 ligand molecules coordinated in monodentate fashion and 3 nitrate ion in bidentate fashion to Eu 3 + to satisfy the 9 coordination of Eu. In case of Cyanex 923 and Cyanex 272 complexes, 3 ligand molecules, 3 nitrate ion and 3 water molecules coordinated to Eu 3 + in monodentate fashion. The Eu complexes of TBP and DHOA were found to have D 3h local symmetry while that for Cyanex 923 and Cyanex 272 were C 3h . Judd–Ofelt analysis of these systems revealed that the covalency of Eu O bond followed the trend DHOA > TBP > Cyanex 272 > Cyanex 923. Different photophysical properties like radiative and non-radiative life time, branching ratio for different transitions, magnetic and electric dipole moment transition probabilities and quantum efficiency were also evaluated and compared for these systems. The magnetic dipole transition probability was found to be almost independent of ligand field perturbation while electric dipole transition probability for 5 D 0 - 7 F 2 transition was found to be hypersensitive with ligand field with a trend DHOA > TBP > Cyanex 272 > Cyanex 923.

Based on photoluminescence spectroscopy it was inferred that uranium stabilizes as both U(IV) as well as U(VI) in Gd2Zr2O7 which was also corroborated using X-ray photo electron spectroscopy (XPS). Absence of equidistant vibronic structure in emission spectrum of Gd1.98U0.02Zr2O7 confirmed that U(VI) stabilizes in the form of UO66−. Based on luminescence lifetime it was inferred that majority of UO66− stabilizes at both Gd3+/Zr4+ whereas U4+ stabilizes only at Zr4+ sites. The positron lifetime doesn’t change on uranium doping indicating the formation of antisite defect. Infact it is this antisite defect in Gd1.98U0.02Zr2O7 which favours the stabilization of its fluorite phase.

Actinide chemistry is very interesting not from scientific perspective but also from technological importance. Elucidating the valence state and coordinating environment of actinide ion like uranium in technologically important magnesium aluminate spinel (MAS) is important to fully understand its hazardous and other harmful effect in human as well as environment. Magnesium aluminate spinel doped with 1.0 mol % of Uranium ion has been synthesized using citric acid assisted gel-combustion route at 800 °C. The as prepared powder is characterised using X-ray diffraction (XRD), time resolved photoluminescence spectroscopy (TRPLS) and density functional theory (DFT) calculations. Uranium is an interesting element because it exhibits multiple oxidation state and each one of them is having characteristics fluorescence behavior. TRPLS is used to investigate the oxidation state and coordination behavior of uranium in MgAl 2 O 4 . Indeed in our earlier work on undoped and lanthanide ion doped MAS; it was oberved that in undoped sample itself defect induced emission could be seen in visible region which was probed using DFT. Here on doping uranium in MAS; complete energy of host is transferred to uranium ion which is explained using DFT. From excitation and emission spectroscopy it was observed that uranium stabilizes in +6 oxidation state in the form of UO 2 2 + ion. Based on luminescence lifetime and its comparison with the emission profile of uranyl fluoride crystal it was inferred that majority of uranium is occupying relatively asymmetric MgO 4 polyhedra and minority substitutes AlO 6 . The site stability of the uranyl ion in MAS was also validated using DFT based first principle calculations. Time resolved emission shows the uranyl at Mg 2+ site differs from the one at Al 3+ site in terms of peak position and intensity.

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.

Optical nanomaterials (ONMs) have attracted significant attention of the global research community owing to their several superior advantages. Some of the ONMs depict negligible photobleaching, bright emission, large electron-hole overlap integral, ease of coating on any surface, large Stoke/Antistoke shifts, higher photostabilites, easy to incorporate inside human body etc. These properties make them technologically highly efficient which helps in minimizing the global issue of energy crisis and improving the standard of living of common man. Several aspects of ONMs such as plasmonic nanomaterials, quantum dots, photonic crystals, and rare earth doped nanoparticles have been discussed. For covering various categories of luminescent nanomaterials (LNMs) based on composition, a brief introduction and importance of metal nanoclusters, carbon nano dots, organic-inorganic nanocomposites, and metal doped nanoparticles have been also included. This review article gives very concise overview of rare earth doped oxide nanoparticles covering several important aspects such as rare earth ion (RE) as dopant, oxide-based host, nanophosphors etc. The importance of LNMs, their advantages as well as drawbacks are also highlighted. Technologically important types of RE doped oxide nanoparticles pertaining to downconversion, upconversion, persistence and radioluminescence are also explained and covered in detail in this review article. Several recent applications involving LNMs in bioimaging, solar cell, thermal sensor, biosensor, anti-counterfeiting etc are explained. In the last section of the review, a comparison between nano and bulk rare earth doped oxide LNMs are discussed in terms of several photophysical properties such as dopant local symmetry, Stark splitting, emission intensity, luminescence lifetime, host to dopant energy transfer, quantum yield etc. Finally, this review article is concluded with summary, outlook, challenges, and future scope on the use of LNMs. Several important aspects of LNMs with focus on RE doped oxide nanoparticles have been covered in this review article which will help general readers in their further research, in this important area, for development of both fundamental sciences and applications involving LNMs.

In this study, we have synthesized Dy 3+ activated Sr 5 (PO 4 ) 3 F (S-FAP) phosphors by sol-gel synthesis method. The synthesized phosphors were characterized by X-ray diffraction pattern (XRD), scanning electron microscopic (SEM), photoluminescence (PL) and thermoluminescence (TL) for structural, morphological and luminescent properties. Dy 3+ activated Sr 5 (PO 4 ) 3 F phosphor shows its characteristic PL emission at 481 nm and 574 nm due to 4 F 9/2 → 6 H 15/2 and 4 F 9/2 → 6 H 13/2 transitions, respectively. TL characteristics of Dy 3+ doped Sr 5 (PO 4 ) 3 F phosphors were taken after irradiation by 60 Co gamma exposure. Two separate TL peaks at 126 °C and 279 °C were observed in case of Dy 3+ doped phosphor. Sr 5 (PO 4 ) 3 F:Dy 3+ phosphor was irradiated within a wide range of exposure of 50 Gy to 7 kGy doses. Linearity was found up to 2 kGy and thereafter TL response saturates. Fading study was also carried out over the duration of six weeks for Sr 5 (PO 4 ) 3 F phosphor. Trapping parameters were calculated using Chen's peak shape method, initial rise method and various heating rate method. Glow curve is deconvoluted using computerized glow curve deconvolution program. TL sensitivity of Sr 5 (PO 4 ) 3 F:Dy 3+ phosphor is found to be less by a factor of 2.08 than commercially used CaSO 4 :Dy phosphor. In order to identify the defect centers formed upon γ -ray irradiation in Sr 5 (PO 4 ) 3 F:Dy 3+ phosphor, EPR measurements were carried out on un-irradiated and irradiated phosphors.

Novel self activated green phosphors; K 2 ZnV 2 O 7 (KZV) and K 2 MgV 2 O 7 (KMV) have been prepared and characterized in details. Both KZV and KMV were prepared by solid state reaction and systematically characterized by a number of techniques like X-ray diffraction (XRD), Fourier transformed Infrared (FTIR), Raman spectroscopy, Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), diffuse reflectance spectroscopy (DRS) and time resolved photoluminescence spectroscopy (TRPLS). XRD studies confirm tetragonal melilite type layered phase for both of them. The presence of pyrovanadate group in both is supported by FTIR and Raman spectroscopic investigations. Raman bands of KMV are blue shifted w.r.t to KZV which may be due to shorter bond lengths of MgO compared to ZnO and lower atomic weight of magnesium compared to zinc. DRS measurements indicated the optical band gap of KMV and KZV are 3.14 and 3.12 eV, respectively. Optical measurements on these samples show the emission of green color on ultra violet light irradiation. The origin of such emission is attributed to electronic transition (charge transfer) from filled 2p orbital of oxygen ion (O 2− ) to vacant 3d orbital of vanadium ion (V 5+ ). In KZV there are dual emission band (PL1 and PL2) which are respectively attributed to 3 T 2 → 1 A 1 and 3 T 1 → 1 A 1 transition, and the emission zone varies slightly compared to KMV. KZV emits bluish green (cool green) where KMV emits in yellowish green (warm green) region. This is indeed an important step towards realization of cost effective rare earth free luminescence material. It is also oberved that PL intensity of KZV is very high compared to KMV which is supported by the lifetime measurements.

Uranium doped Nd2Zr2O7 is synthesized at 800 °C (NUZO-800) using gel-combustion method and characterized using X-ray diffraction, scanning electron microscopy (SEM), X-ray photoelectron microscopy (XPS) and time-resolved photoluminescence (TRPL). As prepared sample was annealed further at 900, 1000, 1100 and 1200 °C leading to increase in the size of the particle and the effect of same has been investigated on the photophysical properties of NUZO. Based on excitation and emission spectroscopy it was inferred that uranium stabilizes as +6 oxidation state in the form of UO 6 6 − . XPS measurement also establishes +6 oxidation state of uranium in Nd2Zr2O7. Both emission intensity and photoluminescence (PL) decay time increases with increase in temperature till 1000 °C beyond which lifetime saturates whereas emission intensity decreases. The decay curve shows two different chemical environments for uranate ion in Nd2Zr2O7 pyrochlore matrix.

Undoped and Mn 2+ doped ZnGa 2 O 4 phosphors were prepared by solution combustion method and characterized by XRD, SEM, luminescence and electron paramagnetic resonance (EPR) techniques. Based on XRD results, it is inferred that, strain in ZnGa 2 O 4 host lattice increases with incorporation of Mn 2+ ions in the lattice. Mn 2+ doping at concentration levels investigated, lead to significant reduction in the defect emission and this has been attributed to the formation of higher oxidation states of Mn ions in the lattice. Electron Paramagnetic Resonance studies confirmed that majority of Mn ions exist as Mn 2+ species and they occupy tetrahedral Zn 2+ site in ZnGa 2 O 4 lattice with an average hyperfine coupling constant, A iso ∼82 G.

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 (La2 Zr2 O7 = 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.

Novel narrow band UVB-emitting phosphors, BaMgF4 :Gd3+ and SrMgF4 :Gd3+ phosphors, were synthesized using a co-precipitation synthesis method. X-Ray diffraction analysis was carried out to confirm compound formation, phase purity and crystallinity of the phosphor. At 274 nm excitation, phosphors show a sharp narrow band emission at 313 nm that can be assigned to 6 P7/2 → 8 S7/2 transition of the Gd3+ ion. With increasing dopant concentration, intensity enhances and then decreases after a certain concentration, which is an indication of concentration quenching taking place in the phosphor. Scanning electron microscopy images of the phosphor show agglomerated particles in the sub-micron range. Particles range in size from 600 to 800 nm. Electron paramagnetic resonance studies of the phosphors were carried out to detect radicals present in the prepared phosphor. With narrow band UVB emission, phosphor seems to be a good candidate for UV phototherapy application. Copyright © 2016 John Wiley & Sons, Ltd.

Selective separation of uranium using bis(2,4,4-trimethylpentyl)phosphinic acid in xylene and C8mimNTf2 was investigated. For ionic liquid based system, the extraction kinetics was found to be slower with the predominance of ion exchange mechanism through [UO2(NO3)·2L]+, while for xylene based system solvation mechanism. The nature of the extracted species was found to be different in both the media as observed in luminescence study. Ionic liquid based system was more radioresistant than that of molecular diluents. Na2CO3 was successfully used for stripping. The selectivity was investigated by processing simulated high level waste of pressurized heavy water reactor origin.

ZnAl2O4:Dy3+ nanoparticles were synthesized using citrate sol–gel method and characterized systematically using X-ray diffraction, scanning electron microscopy and photoluminescence spectroscopy. Emission spectrum of pure ZnAl2O4 shows intense violet blue emission under ultra violet irradiation. Based on electron paramagnetic resonance (EPR) results; it was attributed to presence of singly ionized oxygen vacancy centres in ZnAl2O4. On doping Dy3+ in ZnAl2O4, complete host–dopant energy transfer does not take place. Local structural investigation and lifetime measurements reveal that dysprosium ion is distributed between both Zn2+ and Al3+ sites. Near white light from ZnAl2O4:Dy3+ is attributed to combined host and dopant luminescence. The trap parameters such as activation energy (E) and frequency factor (s) for TSL glow peak 165 °C were determined using different heating rate method. Thermally stimulated emission showed the presence of oxygen related defect centre.

For the first time, visible photoluminescence could be seen in the blue and green regions in Nd2Zr2O7 nanocrystals synthesized by gel combustion at 800 °C. The nanocrystalline nature of samples was confirmed using X-ray diffraction (XRD), and transmission electron microscopy (TEM). The samples were further characterized using Fourier transform infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS). The photoluminescence emissions pointed to the presence of defects related to oxygen vacancies. DFT-based calculations showed that electronic transitions between defect states (which arise due to V1+O and V2+O defects) and the conduction band, as well as impurity states at the bottom of the CB, can lead to emissions in the green and blue regions. Samples were further annealed at higher temperatures of up to 1200 °C to observe the evolution of defects and its implications for the photophysical characteristics of Nd2Zr2O7. The emission intensity was found to increase with an increase in temperature. The increase in intensity upon annealing at a higher temperature was attributed to a reduction in the concentration of surface defects and cation vacancies as confirmed using positron annihilation lifetime spectroscopy (PALS). Based on positron annihilation gamma-ray coincidence Doppler broadening (CDB) measurements, it was observed that the nature of the defects probed by positrons did not change on annealing but their concentrations significantly changed. This was also reflected in the emission spectra, in which the spectral features remained the same but the intensity increased as the annealing temperature was increased. The value of the direct optical band did not change much either as a function of the annealing temperature, which further supports the trend in the emission spectra. In brief, it can be said that the characteristic emission in Nd2Zr2O7 samples is due to oxygen vacancies, whereas the increase in the emission intensity with temperature is due to a decrease in the concentration of cation vacancies and surface defects, which serve as alternative non-radiative paths.

An undoped and Eu3+ doped magnesium aluminate spinel (MAS) was synthesized using a citric acid assisted combustion technique. MAS samples were characterized systematically using X-ray diffraction (XRD), time resolved photoluminescence spectroscopy (TRPLS) and ab initio calculations. On irradiating the undoped MAS with UV light; multicolor emission is observed. The blue emission peak was attributed to Mg2+ vacancies whereas the one in the green region was attributed to oxygen vacancies. Based on the emission spectrum it was inferred that the majority of europium ions are localized at the Mg2+ site which was also confirmed using lifetime measurements. DFT based cohesive energy calculations also showed Eu doping in the Mg position is energetically more favorable than doping in the Al position. Photoluminescence (PL) spectroscopy shows that the emission spectrum consists of host as well as Eu3+ emission indicating the absence of complete host–dopant energy transfer. DFT calculated density of states analysis shows that Eu states are solely localized in VB and CB regions and do not contribute in defects states. From the emission spectrum of the undoped MAS sample it was observed that photo-luminescence properties of the MgAl2O4 are dominantly governed by the defect states coming from the presence of cation and oxygen vacancies (neutral and charged). As a result photon energy transfer from host MAS to dopant Eu is difficult. The actual site symmetry for europium ions in MAS was also evaluated based on a stark splitting pattern which comes out to be C2v. Based on Judd–Ofelt analysis it was found that the Ω2 value is greater than Ω4; indicating high covalency and low symmetry around europium ions which is also observed in the emission spectrum. The high purity of the red emission coupled with good fluorescence quantum yields highlights the potential of this unexplored MAS as a promising phosphor.

SrWO4 (SWO) and Eu3+ doped SrWO4 (SEWO) scheelite samples were synthesized using a polyol method. Crystallite sizes of the as prepared samples annealed at 300 and 500 °C are in a similar range (

Barium zirconate (BZO) nanoceramics were synthesized using self-assisted gel-combustion route. BZO powders were characterized systematically using X-ray diffraction (XRD), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR) and photoluminescence (PL). Doping of Eu3+ and Sm3+ was confirmed by XRD. Intense blue and green emission was observed in undoped sample without activator ion. PL and EPR study shows the presence of oxygen vacancy (shallow and deep defect) is responsible for such visible emission. Bases on PL spectroscopy; it was inferred that majority of Sm3+ ion stabilizes at Ba2+ site without inversion symmetry though oxygen vacancies are introduced in vicinity to ensure local charge compensation whereas majority of Eu3+ ion occupies Zr4+ site. The fact that in Ba1−xEuxZrO3; electric dipole transition (EDT) is much more intense than magnetic dipole transition (MDT); asymmetry ratio is found to be much greater than unity (I⪢1) indicating majority of Eu3+ at site without inversion symmetry in BaZrO3 perovskite. The actual site symmetry for Eu3+ ion in barium zirconate was also evaluated based on stark splitting pattern which comes out to be C6 in BaZrO3.This is also reflected in the trend of Judd Ofelt (JO) parameter; Ω2 value was found to be greater than Ω4 indicating high covalency and low symmetry around Eu3+ ion.

Pure and Eu3+-doped Gd2Zr2O7 pyrochlore was synthesized using a gel combustion method using citric acid as a fuel. Samples of Gd2Zr2O7 pyrochlore were characterized systematically using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and time-resolved photoluminescence spectroscopy (TRPLS). On irradiating the undoped Gd2Zr2O7 pyrochlore with Ultraviolet (UV) light, an intense green emission was observed. Photoluminescence lifetime measurements and X-ray photoelectron spectroscopy (XPS) showed the presence of oxygen vacancies in the pyrochlore sample, which were responsible for the intense green emission in Gd2Zr2O7. Calculations based on density functional theory (DFT+U) of the electronic density of states in the presence of charged oxygen defects qualitatively explained the origin of the green emission in undoped Gd2Zr2O7. The emission spectrum of Eu3+ revealed that it was distributed at both Gd3+ and Zr4+ sites in Gd2Zr2O7, which was also confirmed using lifetime measurements. DFT-based calculations of cohesive energy also showed that doping with Eu is almost equally favorable at Gd and Zr sites. Based on DFT calculations, it is proposed that the distribution of f and d states of Eu3+ atoms matches well with the total density of states (DOS) of ordered Gd2Zr2O7 (o-Gd2Zr2O7), which signifies efficient transfer of photon energy from the host to the Eu3+ dopant. The actual site symmetry of europium ions in gadolinium zirconate was also determined based on the Stark splitting pattern and was found to be D2d, although it is Oh for Gd3+ in Gd2Zr2O7. Calculations of the Judd–Ofelt parameters revealed that Ω2 > Ω4, which indicates high covalency and low symmetry around Eu3+, which is in agreement with the results of emission spectroscopy. The high intensity of the red emission corresponding to the 5D0 → 7F2 transition and good fluorescence yields (51%) highlight the unexplored potential of Gd2Zr2O7:Eu3+ as a promising red phosphor.

A new zirconate-based pyrochlore-type red phosphor, Nd2Zr2O7:Eu3+, was synthesized using the gel-combustion method. The un-doped sample showed visible emission due to the presence of oxygen vacancies. On doping with europium ions, it was found that Eu was distributed into both Nd3+ as well as Zr4+ sites based on emission and lifetime spectroscopy with a lifetime value of 3.35 and 1.14 ms, respectively, although the population at the Zr4+ site is more than that at the Nd3+ site. This is also justified by the presence of two stark components in the 5D0–7F0 transition. The presence of host emission in the spectrum of Nd2Zr2O7:Eu3+ indicated incomplete energy transfer process at low levels of europium doping. Moreover, the efficiency of energy transfer increased as the doping percentage increased, and complete host-dopant energy transfer took place at 5.0% Eu3+ doping. Based on time resolved emission spectroscopy (TRES), the emission spectrum of europium into the Nd3+ sites as well as at Zr4+ sites was elucidated. Calculation of the Judd–Ofelt parameter illustrated that at all europium concentration, the local surrounding area lacks inversion symmetry (asymmetric environment) and the exact point group symmetry was found to be C4. The red purity and high quantum efficiency of Nd2Zr2O7:Eu3+ projects it to be a new materials for commercial application in white light emitting diodes.

Color tunable phosphor has been attracting the scientific community owing to its multifunctional application in optoelectronics, solid-state lighting and bioimaging. Achieving the same in a single host will be quite interesting from a designer’s perspective in narrowing down the cost and scaling it. In the current work, we have explored gel-combustion synthesized rare earth (RE) doped CaZrO3 (CZO) perovskite as a phosphor for covering a wide range of tunable colors ranging from ultraviolet (UV) → Visible. We have doped different rare earth ions such as Sm3+, Eu3+, Gd3+, and Tb3+ in CZO and explored their optical properties, local structure, excited-state lifetime, etc. Doping of RE ions in CZO leads to efficient luminescence facilitated by host→dopant energy transfer. CaZrO3:Sm3+(CZOS) displayed reddish-orange emission with two different lifetime values viz. 20 and 72 μs and are attributed respectively to Sm3+ ion located at Zr4+ (24%) and Ca2+ (76%) sites, respectively. CaZrO3:Eu3+(CZOE) on the other hand, displayed bright, highly pure, and narrow red emission with incredibly low non-radiative transition probability (ANR), high red branching ratio (β2) with internal quantum yield (IQY) of 71.4%. Based on the Stark splitting investigation; europium symmetry in CZOE was found to be quite low with the C6 point group. The lifetime of CZOE though suggested biexponential decay, but Eu3+ ions are localized only at Ca2+ ion; one closer to charge compensating calcium vacancies (194 μs) and other (425 μs) at far off distance from the same. CaZrO3:Gd3+(CZOG) emits highly energetic UV radiation, which can be quite useful in photothermal therapy. Lastly CaZrO3:Tb3+(CZOT) phosphor emits bright green light, but it is displaying a single exponential decay profile stabilizing only on symmetric Zr4+ sites as suggested by the intense magnetic dipole transition (MDT). We believe such a complete spectrum of work in designing a tunable phosphor would be quite beneficial in phosphor converted light emitting diodes (pc-LEDs) employing red-green-blue (RGB) strategy.