Nafa Singh

CaS: Bi as U.V. dosimeter

Abstract Stable CaS: Bi phosphors have been prepared under optimum reducing conditions. These phosphors exhibit two thermoluminescence peaks at 60° and 200°C, except at very low or high concentrations of the dopant. The use of the high temperature (dosimetric) peak in CaS: Bi (0.05%) has suggested for monitoring ultraviolet doses without any pre-irradiation. The effects of annealing, fading, dose response and monochromatic excitation have also been studied.

Thermoluminescence studies of CaS : Bi nanocrystalline phosphors

The thermoluminescence (TL) studies of CaS : Bi nanocrystalline phosphors prepared by the wet chemical co-precipitation method and exposed to γ-rays have been discussed. The average grain size of the samples was estimated as 35 nm using Scherrers equation. The samples exhibit a complex TL glow curve with multiple peaks. Sample exposed to γ-rays showed that the TL intensity increases linearly as the radiation doses increased in the 1.012–40.48 mGy range. The trap parameters namely, activation energy (E), order of kinetics (b) and frequency factor (s) of the main peaks of the CaS : Bi(0.08 mole%) sample have been determined using Chens method. The effect of different dopant concentrations and different heating rates has also been discussed.

Synthesis and luminescence studies of Ce doped SrS nanostructures

Cerium doped strontium sulfide nanostructures were synthesized by the solid state diffusion method in the presence of sodium thiosulfate. XRD confirmed the single phase rocksalt structure of the synthesized samples and the average grain size using the Debye–Scherrer relation is calculated to be 55 nm. TEM micrographs reveal the agglomerated whisker-like morphology with a diametre of 55–60 nm and length of several nanometres, which is in close agreement with XRD results. The effect of dopant concentration on photoluminescence (PL) intensity has been studied. PL emission for SrS : Ce (0.5 mol%) is at 481 nm with a shoulder at 530 nm at an excitation wavelength of 430 nm, which is attributed to the transitions from the 5d state to the 4f (2f7/2, 2f5/2) states of Ce3+. Ultraviolet and visible (UV–VIS) spectroscopy shows band-to-band absorption at 273 nm (4.54 eV), which is blue shifted in comparison to the band gap of bulk SrS (4.2 eV), which may be due to quantum confinement. The effect of high energy ball milling on the grain size and PL intensity has also been investigated for the first time in the doped SrS system. The PL emission wavelength is blue shifted by 3 nm but the emission intensity decreases unexpectedly as the milling time increases, although there is a reduction in size which is evident from XRD peak broadening of the milled samples. This may be ascribed to surface defects generated by ball milling which act as killing centres, quenching the PL.

Spectral variations and retrapping processes in CaS:Bi dosimeter

Abstract Thermoluminescence spectra of CaS:Bi dosimeter have been recorded for the two glow peaks occuring at 60°C and 200°C. Due to the presence of two groups of traps, retrapping mechanism has been investigated in order to get the best performance out of this dosimeter. The effect of annealing, storage and pre-heating on the spectral characteristics has also been studied. The shift of the band maximum to longer wave length at higher temperature has been briefly discussed on the basis of one kind of luminescence centres.

Synthesis and characterization of bismuth doped calcium sulfide nanocrystallites

Nanosized bismuth doped calcium sulfide (CaS:Bi) particles have been synthesized by a wet chemical co-precipitation method. The average size of the nanoparticles was found to be about 30?nm. The particles were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), UV?vis spectroscopy and fluorescence spectroscopy. The effect of particle size on the photoluminescence (PL) of CaS:Bi has been studied. The optimum dopant concentration was found to be 0.025?mol% of bismuth for maximum PL emission intensity. A comparative study between bulk CaS:Bi prepared by a reduction method and nanosized CaS:Bi made by the wet co-precipitation method has been carried out. Increase in band gap with decrease in particle size has been explained on the basis of the quantum size effect. The PL intensity of the nanoparticles was found to increase to almost twice that of the bulk particles. The effect of different dopant concentrations on emission intensity has also been studied.

Luminescence studies and effect of etching on cerium-doped CaS nanoparticles

Cerium-doped calcium sulphide nanoparticles were synthesized using the solid state diffusion method. The formed nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-visible absorption spectroscopy and photoluminescence (PL) spectroscopy. The XRD pattern confirmed a cubic CaS phase with an average grain size of 53 nm of the formed samples. The TEM image showed non-agglomerated particles with an average size of 60 nm, which is in close agreement with the XRD result. The PL-emission spectrum showed peaks at 506 and 565 nm due to the transition from the excited state to the ground state of Ce3+. The effect of etching has been studied on the luminescent properties of CaS:Ce phosphors. With an increase in the etching time there is decrease in the size of the particles, as a result of which the PL spectrum showed a slight blue shift. The UV-visible absorption spectrum also showed a blue shift with an increase in etching time, which is in agreement with the nanosize effect.

Thermoluminescence and dosimetric properties of bismuth doped CaS nanocrystalline phosphor

The irradiation effect on bismuth doped CaS nanocrystalline phosphors and their possible applications to solid state dosimetry have been studied. The wet chemical co-precipitation method has been used for preparation of nanocrystallites. In UV exposed CaS nanocrystallites, the thermoluminescence glow curve consists of two peaks at 439 and 561 K. The effect of different concentrations, dose dependence, fading and reusability in CaS:Bi nanocrystallites have been investigated. The high temperature peak (dosimetric peak) intensity is nearly linear in a wide range of UV exposure. A blue shift has been observed in photoluminescence spectra, which may be attributed to quantum size effect.

Photoluminescence and optical characterization of CdS nanoparticles prepared by solid-state method at low temperature

The photoluminescence (PL) and optical properties of CdS nanoparticles prepared by the solid-state method at low temperature have been discussed. The effects of NaCl and anionic surfactant SDBS (sodium dodecylbenzene sulfonate) on the luminescent properties of CdS nanophosphors prepared using this method, without the inert gas or the H2S environment, were studied separately. The synthesized products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscope (FESEM), and energy dispersive X-ray spectroscopy (EDAX). UV–VIS absorption and PL spectra were also studied. XRD studies confirmed the single-phase formation of CdS nanoparticles. TEM micrograph revealed the formation of nearly spherical nanoparticles with a diameter of 2.5 nm. The PL emission for the CdS shows the main peak at 560 nm with a shoulder at 624 nm, with an increase in the PL intensity after the addition of SDBS. The effect of Mn doping on PL intensity has also been investigated. The PL spectra show that the emission intensity decreases as the dopant concentration increases.

UV dosimetry by thermoluminescence of bismuth doped CaS

The preparation of highly thermoluminescent bismuth doped CaS phosphors, where no pre-irradiation is required for measuring ultraviolet doses is reported. These phosphors exhibit two TL peaks above room temperature when excited by UV light. The effect of dopant concentration and flux is evaluated for maximising the dosimetric peak. The phosphor is annealed before studying its spectral response, fading and dose linearity. It is found that under suitable conditions of preparation the CaS:Bi(0.025%) phosphor has the potentiality to monitor ultraviolet radiation of wavelength less than 370.0 nm.

Operational importance of some physical parameters of TL phosphor CaS:Bi

Abstract The change in TL response due to change in phosphor grain size, grinding time, ambient illumination levels, thickness of phosphor layer, annealing and irradiation temperatures of CaS: Bi has been studied. Thermoluminescence (TL) response has been found to increase with the decrease of grain size due to the generation of surface traps. However, after an initial increase, a gradual decrease in TL response has been observed with the increase in grinding time. Irradiation in the presence of fluorescent room light has been found to enhance the error in the dose measurements by 16%. Decrease in TL response when the phosphor is irradiated at elevated temperature has shown that trapping levels corresponding to two peaks behave independently. From these investigations optimised conditions for dose measurements have been concluded.