Distinct differences observed in the alternating current powder electroluminescence (ACPEL) and photoluminescence (PL) characteristics of lab-made ZnS:Cu(1%) phosphor have been explained based on variation in donor and acceptor traps (levels) assisted electron-hole recombination upon optical and electrical excitations. The results were also compared with that of commercially available ZnS based phosphor. The fabricated display panel using lab-made ZnS:Cu(1%) sample exhibit bright blue colour electroluminescence. On the other hand, device fabricated using commercially available phosphor display bright cyan colour emission under similar biasing conditions. It is confirmed that the commercially available phosphor is composed of both cubic and hexagonal phases of ZnS whereas the lab-made sample is single phase cubic ZnS. The observed variation in spectral profile for commercial sample with increase in frequency of applied AC signal has been explained based on coexistence of hexagonal and cubic phases of ZnS in the sample.

Structural as well as magnetization studies have been carried out on graphite samples irradiated by neutrons over 50 years in the CIRUS research reactor at Trombay. Neutron diffraction studies reveal that the defects in irradiated graphite samples are not well annealed and remain significant up to high temperatures much greater than 653 K where the Wigner energy is completely released. We infer that the remnant defects may be intralayer Frenkel defects, which do not store large energy, unlike the interlayer Frenkel defects that store the Wigner energy. Magnetization studies on the irradiated graphite show ferromagnetic behavior even at 300 K and a large additional paramagnetic contribution at 5 K. Ab-initio calculations based on the spin-polarized density-functional theory show that the magnetism in defected graphite is essentially confined on to a single 2-coordinated carbon atom that is located around a vacancy in the hexagonal layer.

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 similar to 3.7 ms and point group symmetry similar to C-6v. Judd-Ofelt analysis suggested very low non-radiative channels present in DES resulting in extremely high quantum yield similar to 76% and very high color purity of 94.72% which was also assisted by absence of any water molecule as suggested by FTIR measurement.

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.

Designing of efficient luminescent materials requires proper understanding of energy transfer, defect evolution and dopant local structure. The present work is a perfect amalgam wherein we have thoroughly investigated the concentration dependent host sensitized energy transfer, defect evolution and local structure of europium ion in La2Ce2O7 (LCO) pyrochlore material. Raman spectroscopy suggested stabilization of defect fluorite structure for LCO as well as LCO:Eu3+ (LCOE) but degree of structural distortion as well as oxygen vacancies (OVs) increases with increase in europium ion concentration. Diffuse reflectance spectroscopy suggested band gap narrowing at higher doping level owing to enhanced density of OVs. Positron annihilation lifetime spectroscopy suggested an increase in the formation of oxygen vacancies and vacancy clusters near the surfaces at higher doping. As a result, LCO, on irradiation with 250 nm ultraviolet photon showed visible emission due to OVs as well charge transfer transition. On Eu3+ doping emission spectra was rich in host as well as europium emission and host to europium energy transfer increases with increase in europium ion concentration. This get's reflected as violet blue emission at lower doping and yellowish white at higher doping level >= 7.5% under host excitation and orange-red emission under 471 nm dopant excitation. Europium ion emission spectral profiles in LCOE suggested stabilization of Eu3+ in CeO6 octahedra as is also confirmed using lifetime spectroscopy. Judd-Ofelt measurement further reflected higher branching ratio for D-5(0)-> F-7(2), internal quantum yield similar to 48% and high Omega(2) compared to Omega(4). This work highlights the importance of local dopant site, HSET, excitation photon and defects in designing color tunable luminescent materials and is expected to play an important role in designing the phosphor converted light emitting diodes (pc-LEDs).

Conventional characterization of plutonium contaminated neoprene gauntlets and cellulosic materials are highly difficult not only due to the non-geometric and unconventional nature of the sample, but also the radio-toxicity associated with them. An analytical method based on direct current arc atomic emission spectrometric (D.C.Arc AES) technique was developed for direct determination of 22 metallic impurities in contaminated neoprene gauntlets and cellulose samples. The samples were incinerated to powder form and analyzed against seven point standardization using graphite standards. The interference free best performed emission lines of the analytes were chosen as the analytical lines for establishing the calibration curves required for their estimation. The linear dynamic range, sensitivity, detection limit, precession associated with these analytical lines were evaluated in the graphite matrix. Energy dispersive X-ray fluorescence spectrometry has also been employed for comparative evaluation of the analytical performance of the developed AES based method as well as analysis of the actual samples. D.C.Arc AES based method was found to have 20% precession, while that for EDXRF was 10%. However, elements with lower Z values and lower concentration can only be determined by AES.

UV emitting Gd3+ doped phosphors have recently attracted significant attention among materials scientists owing to their important applications in the areas of photothermal therapy, transilluminators and sensitizer based luminescent phosphors.

An effort was made to get an idea regarding the correlation between structure and radiative properties of Gd incorporated LiBaB9O15 matrix. The samples were synthesized via a combustion route and characterized using X-ray diffraction (XRD). Photoluminescence (PL) experiments were carried out in order to understand the radiative properties and local site symmetry of ‘Gd’ ions in the sample. The site occupancy of the rare earth ions were also evaluated through electron spin resonance (ESR) measurements. The PL data suggested the emanation of UV light from the system with emission maxima at 307 and 311 nm. Both these peaks belong to the UV-B region which has many useful applications in phototherapy. The nature of the peaks suggested the stabilization of the ion predominantly in asymmetric geometry making the electric dipole transitions more prominent. It was observed that the maximum radiative or luminescence intensity could be obtained for the 0.048 mol ‘Gd’ doped sample. Beyond this, concentration quenching reduced the PL intensity. Based on the energy transfer model it was evaluated that ‘Foster’ type mechanism was responsible for the observed concentration quenching. From the ESR data it could be inferred that the rare earth ion stabilises at two different sites with differing geometries. At lower doping levels, it was seen that the Gd3+ ions predominantly existed at relatively more distorted Ba2+ sites and at higher concentrations, the ions are at the distorted sites as well as at Ba2+ sites with less distorted environment.

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 -Oil and PO(4)(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, Intrapartide 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.

Lanthanide luminescence gains significant attention during the last decade or so because of its unique optical properties. In designing a phosphor material various parameter needs to be optimized as far as lanthanide doped materials are concerned, such as host-dopant energy transfer, the local structure of lanthanide ion, point group symmetry of lanthanide ion, etc. In this context, we have explored a variety of novel oxide hosts for lanthanide based luminescent materials. In this review, we have explored the optical properties of various lanthanide ions doped in multiple sites host such as Sr2SiO4, Sr2CeO4, SrZrO3, Zn2P2O7, Gd2Zr2O7, Nd2Zr2O7 etc. and correlate the results with the one reported in literature. The focus was on establishing structure-property correlation, identifying the dopant local site, understanding the dynamics of host to depend energy transfer, defect related emission etc., which are especially important for designing tunable phosphors for optoelectronic devices. Europium ion was used as a spectroscopic probe to decipher its point group symmetry and correlate it with the structure of the host materials. Defects are not always deleterious and can sometime leads to interesting optical properties and few nano and bulk materials were synthesized wherein visible blue-green emission could be seen due to the presence of oxygen vacancies and other defects. (C) 2020 Elsevier B.V. All rights reserved.

Wurtzite form of ZnS has been prepared by heating zinc ethane thiol complex at a relatively low temperature of less than 300 °C. This low temperature synthesized, high temperature form of ZnS is quite stable and does not undergo conversion to cubic form even at annealing temperatures as high as 900 °C. The “c/a” ratio of ZnS lattice decreases whereas average crystallite size and “I(hkl)/I(002)” ratio increase with increase in annealing temperatures up to 700 °C and remains same for samples heated at 800 and 900 °C. Although crystallite sizes remain same for 800 and 900 °C heated samples, carbon species get removed from the lattice with increase in annealing temperatures and this is further confirmed by decrease in value of strain, FTIR and luminescence results. The synthesis method also can be used for doping transition metal ions such as Mn2+ in ZnS lattice. EPR Studies confirmed incorporation of Mn2+ ions at Zn2+ site in ZnS lattice.

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.

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 is 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 (A(NR)), high red branching ratio (beta(2)) 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 C-6 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 us) and other (425 mu s) 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. (C) 2020 Elsevier B.V. All rights reserved.

Considering the positive implication of designing singular emitting phosphor in the area of bioimaging and solid state lighting, this work reports on singular orange emission from Zn2SnO4:Eu3+ (ZSOE) phosphor. The studies showed that ZSOE is stabilized in inverse spinel structure with Eu getting stabilized in octahedral Zn sites with orthorhombic symmetry and D-2h point group leading to very intense orange emission with negligible red component. Undoped Zn2SnO4 (ZSO) on ultraviolet irradiation depicted defect induced blue emission due to synergetic effect of F-centers and vacancy clusters. (C) 2020 Elsevier B.V. All rights reserved.

This work highlighted green, red, and white light emission from a single K2Th(PO4)2 compound consisting of actinide and an alkali ion through defect, doping, excitation, and energy transfer manipulation.

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 beta-Ag2MoO4 using simple co-precipitation method under neutral conditions. Pure beta-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 beta-Ag2MoO4 takes place via Dexter mechanism of exchange interaction. Additionally, on doping Dy3+ ions in the beta-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.

A methodology was optimized for the determination of fission products in irradiated thoria. Chlorinated cobalt dicarbollide (CCD) and tri-n-butyl phosphate (TBP) were employed for the separation of U and Th, respectively, for dose reduction and to avoid spectral interferences arising out of the emission rich spectra of U and Th. The tolerance level of U and Th on these analytes was found to be 100 mg L-1 and 125 mg L-1 respectively. Five contacts of TBP were required for preferential separation of U and Th. CCD formed a Cs+CCD- complex through an 'ion exchange' mechanism, while TBP formed UO2(NO3)(2)center dot 2TBP and Th(NO3)(4)center dot 3TBP complexes through a 'solvation' mechanism.