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Phosphoric acid/hydrogen peroxide (H3PO4/H2O2) oxidizer mixture is used to grow films on high purity germanium (HPGe) crystals in Hydrofluoric acid with an objective to passivate the inter-contact region of HPGe detectors. The bonding characteristics have been investigated by IR transmission. The native oxide films consist of Ge-O bonding in cristalobite atomic configuration where both hexagonal and tetragonal germanium oxide signatures are present. Raman spectroscopy data indicate the amorphous nature of grown films. Scanning electron microscopy (SEM) clearly reveals formation of a porous layer that is Ge–Hx terminated as indicated by FTIR spectroscopy when high peroxide concentrations are employed for growth. On the other hand smooth and dense films appear at low H2O2 concentration with no Ge-H bonding signature. The chemically grown films are quite stable in HF unlike the unstable nature of native oxides of Ge. HPGe diode has been fabricated using lithium diffused and Pd surface barrier contacts. The inter-contact region is passivated using chemically grown oxide film. The film offers high resistive properties and inhibit surface leakage problem of the fabricated diodes. [ABSTRACT FROM AUTHOR]

Partially transparent ceramic of 2 at.% Eu doped CaF2 have been grown preferentially towards [111] direction. For this purpose, Eu doped CaF2 nanoparticles (size~12 nm) obtained by a low temperature solution growth method has been pressed at 1000°C under vacuum. The preferentially grown ceramic shows 15% transparency within the visible range of spectrum. As confirmed by the X-ray diffraction result, the hot pressed ceramic exhibits reduced lattice volume than the nanopowder. It indicates Eu3+ as the dominant substituting ions at the Ca2+ sites of CaF2 lattice in the hot pressed ceramic material. It is corroborated by the photoluminescence results of hot pressed ceramic which shows strong red emission corresponding to Eu3+ sites. However, photoluminescence of nanopowder exhibits intense peak in the blue region of the spectrum which is characteristics of Eu2+ sites. [ABSTRACT FROM AUTHOR]

Epitaxial films of 2 at.% Eu doped CaF2 have been grown on (111) plane of CaF2 by a low temperature solution growth method. The CaF2: Eu films when grown on Si (111) and glass substrate show random orientation having higher degree of surface roughness. As confirmed by the X-ray diffraction and photoluminescence results, Eu (II) ions substitute the Ca sites of CaF2 lattice. Excitation spectrum shows two broad peaks at 282 and 366 nm, which correspond to the allowed transitions of 4f7 to 4f65d1 (eg) and 4f65d1 (t2g) of Eu2+, respectively. Photoluminescence of Eu (II) doped CaF2 films exhibit intense and sharp peak in the blue region of the spectrum. [ABSTRACT FROM AUTHOR]

Temperature dependent photoluminescence (PL) spectroscopy has been employed to study the exciton localization in ZnO nanostructures of various sizes. Low temperature (LT) near-band-edge UV emission from ZnO nanostructures of size less than 100 nm show signature of free exciton (FE), bound exciton and longitudinal-optical phonon replica of FE lines. Free and bound excitonic emission deviates from the Varshni equation at LT and exhibits S-shaped temperature dependence due to the exciton localization effect. Deviations of the measured data from the Varshni equation directly provide the exciton localization energies, ELoc. It was found that ELoc increases and dELocalization due to thermal activation occurs at higher temperature for smaller nanoparticles. [ABSTRACT FROM AUTHOR]

Thin films of thallium activated cesium iodide (CsI: Tl) have been deposited on silicon substrates using a thermal evaporation technique. The films were found to have similar luminescence properties as bulk single crystals and the Tl ion concentration could be controlled by varying the film thickness. These can be used with P-I-N photodiodes in the radiation detection applications. [ABSTRACT FROM AUTHOR]

High quality lithium tetraborate; Li2B4O7 (LTB) single crystals with varying concentrations of Ag have been grown using the Czochralski technique. Optimized growth parameters enabled us to grow crystals that were transparent, colorless, crack-free, and core-free. The grown LTB:Ag crystals were characterized using UV-VIS-NIR transmission, photoluminescence (PL) and thermoluminescence (TL) measurements. The transmission of about 85 % in the range from 200 nm to 1100 nm revealed a good optical quality of the grown crystals. The TL glow peak of LTB:Ag single crystals at 160°C with an emission at 270 nm is found useful for the dosimetric applications. The dose response is found to be linear in the range from 100 mGy to 50 Gy. [ABSTRACT FROM AUTHOR]

High optical quality Li2B4O7 (LTB) single crystals and glassy phases of pure, doped (Cu, Ag) and co-doped with Cu+Ag have been grown by Czochralski crystal pulling and melt quenching techniques respectively. They were characterized through photoluminescence (PL), thermoluminescence (TL), and UV-VIS-NIR transmission measurements. The PL of glass phase shows light yield comparable to that of single crystal. 80-85 % optical transmission in the range 350-800 nm revealed good optical quality of the glasses which is comparable to the single crystals though the glasses have higher cut off wavelength (lower energy). TL glow peaks of Cu doped LTB single crystal at 200 °C and for Cu+Ag co-doped LTB single crystals at around 170°C and 240°C are useful for the dosimetry applications and found to be linear in the range from 1mGy to 1kGy. However, in glasses no TL was observed in spite of a good PL yield. [ABSTRACT FROM AUTHOR]

Nano-particles of CaF2: Mn were synthesized by a co-precipitation method. Optically transparent ceramics were obtained by vacuum hot-pressing at 1000°C under 20 MPa pressure for 2 h. The duration of pressure and dehydration of the initial powder was found important to achieve the transparency. 50% transparency was observed for a polished disc of 1 mm thickness. SEM micrographs revealed the absence of voids in hot pressed samples. These samples were found to be highly sensitive and linear for TLD and can measure doses from mGy to kGy. [ABSTRACT FROM AUTHOR]