S. G. Singh

Growth and characterization of lithium yttrium borate single crystals

Single crystals of 0.1% Ce doped Li6Y(BO3)3 have been grown using the Czochralski technique. The photoluminescence study of these crystals shows a broad emission at ∼ 420 nm corresponding to Ce3+ emission from 5d→4f energy levels. The decay profile of this emission shows a fast response of ∼ 28 ns which is highly desirable for detector applications.

Preparation and characterization of CsI:Tl thick films on silica glass substrate

The films of Tl doped CsI (CsI:Tl) of varying thicknesses ranging from 10 μm - 1.5 mm have been grown on silica glass substrates by thermal evaporation technique. Effects of substrate temperature, substrate surface texture and film thickness on the film structure and morphology were studied. The film shows a preferred orientation along the direction having columns of diameter 1–6 μm depending on the film thickness. In the films of lower thicknesses a number of cracks were observed that vanishes with increase in the film thickness and shows a continuous and crack-free morphology beyond 500 μm thickness. Radio-luminescence of the films was also recorded using a white x-ray source (Cu target) and a solid state spectrometer in 300–800 nm wavelength range.

Synthesis of gadolinium silicate by hydrothermal method

A simple method based on hydrothermal synthesis of materials to prepare gadolinium silicate has been prescribed. It is found that molar ratio of Gd(NO3)3: TEOS plays a crucial role in the formation of Gd2SiO5. The effect of calcinations, concentration of the precipitating agent and dopant atoms on composition and morphology of the synthesized materials has been investigated. The desired phase of Gd2SiO5 can be synthesized from hydrothermally grown powder after annealing at 1400°C.

Synthesis of optically transparent ceramic of CaF2 doped with Mn and Ce for thermoluminescent dosimetry

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.

Growth and luminescence properties of Ce doped Li6Gd(BO3)3 single crystals

Large size single crystals of undoped and Ce doped Li6Gd(BO3)3 oriented in direction have been grown using the Czochralski technique. The Transparency of these crystals was >85%. The Low temperature photoluminescence study of these crystals revealed that the temperature quenching of Ce3+ emission is compensated, to some extent, by an increased energy transfer between Gd3+ →Ce3+ with temperature.

Synthesis And Luminescence Studies Of Mn doped CaF2

Nano particles of CaF2:Mn were synthesized by a co‐precipitation method. The maximum Mn concentration which could be doped into the CaF2 lattice was ∼3%. The photoluminescence and thermally stimulated luminescence (TSL) were studied for different Mn doping. High dopant concentration leads to the appearance of yellow orange luminescence (580 nm) band due to the introduction of excitation levels in the deep UV region. A slight decrease in TSL peak temperature was observed at higher Mn concentrations after attaining a maximum at 1.3% Mn. Based on TSL data optimum doping concentration was found to be 2.5%. These nanoparticles were further hot pressed in vacuum to produce optically transparent ceramic.

Scintillation yield uniformity studies on single crystals of Tl doped CsI

Single crystals of 0.1% Tl doped CsI (50 mm φ and 50mm L) have been grown using the Bridgman melt growth technique. Scintillation yield uniformity of radiation detector made from the as-grown crystals was checked using an 243Am α (5.25 and 5.5 MeV) source. It was found that yield variation along the radial direction was within 2% over 0-15 mm and was less than 5% for the whole crystal. A correlation between radial temperature profile of furnace and yield uniformity was observed.

Effect of film thickness on luminescence property of CsI: Tl

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.

Czochralski Growth of NaY(WO4)2 Single Crystals

Single crystal growth of NaY(WO4)3 was carried out by the Czochralski technique using a starting charge rich in Y2(WO4)3 composition. This off‐stoichiometric starting composition used for the growth has been found to yield reasonable size single crystals. The XRD measurements carried out on the powder from different positions of the grown crystal confirmed the presence of desired single phase NaY(WO4)2. Grown crystals were found to have good transparency.

Photoluminescence Studies on NaBi(WO4)2 Single Crystals at Low Temperatures

Photoluminescence properties of NaBi(WO4)2 crystals were studied near liquid nitrogen temperatures. The excitation and emission properties were found to be similar to an iso‐structural Scheelite PbWO4. A metal‐to‐metal charge‐transfer character (Bi3+→W6+) is found responsible for the emission process. The thermal activation energy for quenching of the luminescence was found to be about 160 meV.