[en] Experimental methods are outlined for the preparation of hard, semitransparent, diamond-like carbon films on oriented, polished crystal wafers of silicon and gallium arsenide as well as on potassium bromide flats, quartz plates, and glass plates. Properties of the films are determined using infrared and visible absorption spectroscopy, ellipsometry, Auger, ESCA and conductance capacitance spectroscopy. Preparation techniques include rf plasma decomposition of hydrocarbons (methane, ethylene, propane and propylene) and dual ion beam sputtering. In general, the films showed slight, or no traces of oxygen. The maximum optical bandgap obtained was 2.7 eV. In the other part of the work, highly graphitized pitch-based carbon fibers were intercalated with copper chloride, antimony pentachloride, iodine chloride, nitric acid and bromine. These were reacted either singly or sequentially. The electric resistivities were measured before and after incalation, in air, and tests for air and thermal stability were done. A quantitative measurement of mobility was made using the Shubnikov-deHaas effect

[en] X-ray induced redox processes in YVO₄:Bi³⁺, Sm³⁺ phosphor were investigated using its photo-luminescence behaviour. A mechanism has been proposed for the electron release and trapping by the dopant ions. It is proposed that lanthanide vanadates might be potential matrices for immobilization of radioactive fission products. (author)

[en] Highlights: • Synthesis of SrBPO₅:U phosphor by solid state route. • Confirmed the stabilization of uranium as UO₂²⁺. • Evaluation of order of kinetics and trap parameters of the system. • ESR-TSL correlation of the observed glow peak. • Probable mechanism proposed for the TSL glow peak. - Abstract: Un-doped and uranium doped SrBPO₅ samples were synthesized using solid-state reaction route and investigated for their photo and luminescence properties. Photoluminescence (PL) spectrum of uranium doped sample showed five peaks at 502, 524, 547, 569 and 597 nm. The average frequency of symmetric stretching of O=U=O in the ground electronic state was found to be about 757 cm⁻¹. PL decay time measurements on the system confirmed the stabilization of uranium as UO₂²⁺ in the matrix. Thermally stimulated luminescence (TSL) measurements carried out on gamma irradiated SrBPO₅:U sample showed a glow peak at 390 °K, whose spectral characteristics was found to be typical of UO₂²⁺. The trap parameters were evaluated using different heating rate method. Room temperature EPR data suggested the formation of borate and oxygen based radical centers in the gamma-irradiated sample. Detailed EPR-TSL correlation studies confirmed the destruction of the oxygen radical to be responsible for the observed glow peak

[en] Photoluminescence (PL) and Thermally stimulated luminescence (TSL) properties of both virgin and Ce doped ZnAl₂O₄ phosphors were investigated. The phosphors were synthesized via sol–gel route using the respective metal nitrates and citric acid. The nano particle nature of the phosphor was confirmed by X ray diffraction and dynamic light scattering techniques. Time resolved photoluminescence and photo-acoustic spectroscopic techniques were used to characterize the emission and excitation properties of the system. TSL properties of the nanophosphor showed a single glow peak at 468 K. Various trap parameters and the kinetics for the glow peak were evaluated assuming the Arrhenius behavior for the system. Electron spin resonance (ESR) technique was used to identify the chemical nature of the traps/defects responsible for the glow peak. The emission spectrum of the nanophosphor was plotted on a standard CIE diagram which suggested a strong bluish violet emission from the phosphor system. Further, the intensity of the phosphor was compared with that of commercial blue phosphor to know the commercial utility of the prepared phosphors. - Highlights: • Synthesis of ZnAl₂O₄:Ce nano-phosphors by sol–gel route. • Speciation of Ce in the host matrix. • Evaluation of order of kinetics and trap parameters of the system. • ESR–TSL correlation of the observed glow peak. • Evaluation of CIE indices and commercial utility of the blue emitting phosphor

[en] The existence of a permanent electric-dipole moment (EDM) in a particle implies that both parity (P) and time-reversal symmetry (T) are violated. We propose an experiment to search for a permanent atomic EDM using laser-cooled ¹⁷¹Yb atoms launched in an atomic fountain. A uniform B field sets the quantization axis, and the Ramsey separated-oscillatory-fields method is used to measure the Zeeman precession frequency of the atoms. Laser beams of appropriate polarization are used for preparation and detection in a given magnetic sub-level. The signature of an EDM is a shift in the Ramsey resonance correlated with application of a large E field. The precision is expected to be at least 20 times better than current limits because the use of a cold atomic beam allows application of E field 10 times larger than in a vapor cell, and the interaction time with the E field is 200 times larger compared to a thermal beam. The leading source of systematic error in beam experiments, the motional magnetic field, is reduced considerably because of the near-perfect reversal of velocity between up and down trajectories through the E-field region. (authors)

[en] Thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) studies were conducted on self-irradiated as well as gamma irradiated BaCO₃ co-doped with ²³⁷Np⁴⁺ and NO₃^- ions. EPR studies of the irradiated samples revealed that the electron transfer process between iso-electronic carbonate and nitrate groups is the dominant effect of ionizing radiation, forming CO₃^- and NO₃^2- ions. This facilitated the radiation stability of the valence of Np in the tetravalent state. TSL spectral studies showed that Np⁴⁺ ion acts as the luminescence centre. TSL-EPR correlation studies revealed the role of CO₃^- ion in the glow peak at 413 K

[en] Thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) studies were carried out on cerium doped and cerium-uranium co-doped K₃Na(SO₄)₂ samples after γ-irradiation. Three glow peaks around 352, 415 and 475 K were observed and their spectral characteristics have shown that Ce³⁺ and UO₂²⁺ act as the emission centres in K₃Na(SO₄)₂:Ce and K₃Na(SO₄)₂:Ce, U, respectively. In Ce-U co-doped sample, energy transfer from cerium to uranium takes place. The commonly occurring radiation-induced centres in sulphates, viz SO₃^- and SO₄^- were observed by EPR and SO₄^- radical ion was found to take part in the TSL emission at 415 K. The hitherto unknown information, however, is the formation of SO₄^--SO₃^- radical pair creating deep traps in these lattices, apparently assisted by the dopants. This is the first observation of such radical pair formation leading to the identification of deep traps in this lattice. The radical pair, (SO₃^--SO₄^-) which is stable up to 970 K, decreases the intensity of the peak at 415 K due to the depletion of SO₄^- centres

[en] Main thrust of this work includes exploring lanthanide luminescence for structural probe, synthesizing white light emitting materials and understanding defect induced emission in nanomaterials. Refractory materials like zirconia and thoria doped with Eu³⁺ have been synthesized at a low temperature using reverse micellar route and investigated the photoluminescence properties of Eu doped ThO₂ and ZrO₂. Luminescence properties of Eu, Dy and Sm in strontium silicate and their local site occupancy have been described. EXAFS measurements and theoretical calculations have been carried out to justify the experimental results. In SrZrO₃, PL findings show that Eu³⁺ ions occupy both Sr²⁺ and Zr⁴⁺ sites and their spectral characteristics are entirely different. Optical properties of Sm, Gd and Dy doped SrZrO₃ have also been discussed. Rare earth free blue emitting Sr₂CeO₄ has also been synthesized. An entirely new phosphate based phosphor; zinc pyrophosphate has been explored. The effect of zinc coordination on the photophysical properties of lanthanide and transition metal ion was also studied. (author)

[en] Samarium doped SrBPO₅ phosphor was synthesized by a high temperature solid state reaction route and its luminescence properties were investigated before and after gamma irradiation. A photo-acoustic spectroscopic technique was used to record the excitation/absorption spectrum of the sample. Photoluminescence studies on the sample prior to gamma irradiation confirmed the presence of Sm³⁺ at an asymmetric site. After 2 kGy of gamma irradiation, the sample showed strong afterglow without any external source that lasted for several minutes. Thermoluminescence (TSL) studies revealed the presence of glow peak at 323 K for the system. Electron spin resonance (ESR) studies suggested the formation of borate and oxygen based radical centers in the gamma irradiated system. Detailed ESR–TSL correlation study confirmed the destruction of the oxygen radical to be responsible for the observed glow peak. Based on the findings, a probable mechanism was proposed for the glow peak and observed afterglow. - Highlights: • Synthesis of SrBPO₅: Sm by the high temperature reaction route. • Prior to irradiation, Sm³⁺ stabilized in an asymmetric site, no evidence for Sm²⁺. • Observation Sm³⁺ afterglow after gamma irradiation without any external source. • ESR–TSL correlation study of the irradiated system. • Proposition of a plausible mechanism for the TSL glow peak and afterglow

[en] Graphical abstract: - Highlights: • Synthesis of undoped and Eu and Tb-doped and Eu–Tb co-doped Strontium Molybdate (SMO) by co-precipitation method. • Characterization of the samples by XRD, SEM and DLS for particle size. • Observation of orange-red emission and blue-green emission from the Eu-doped and Tb-doped samples, respectively. • Optimization of the dopant ion concentration for white light emission from the co-doped sample. • Observation of cool day light white light emission with CCT 6863 K from the co-doped system (Eu-0.5 mol% and Tb-1 mol%). - Abstract: Nano ceramics of undoped and Eu and Tb-doped strontium molybdate (SMO) were synthesized via co-precipitation route and characterized by XRD, SEM and DLS techniques. It was observed that the average particle size for the samples was 90 nm. A bluish emission attributed to the tetrahedral molybdate moiety was observed for the undoped system. The single-doped sample Eu"3"+:SMO gave orange-red emission, whereas the Tb"3"+:SMO sample showed blue-green emission. From the emission data, the site symmetry of the ions was estimated. Based on the emission data of single-doped samples, the co-dopant ions concentrations were tuned to extract white light emission from the system. It was observed that when doped with 0.5 mol% Eu"3"+ and 1 mol% Tb"3"+ and excited with 230 nm, the system gave a ‘cool day light’ white light emission with a correlated color temperature (CCT) 6863 K.