Dr. Giri Dhari Patra | Bhabha Atomic Research Centre (original) (raw)
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Papers by Dr. Giri Dhari Patra
AIP Conference Proceedings, 2012
ABSTRACT High optical quality Li2B4O7 (LTB) single crystals and glassy phases of pure, doped (Cu,... more ABSTRACT 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.
Journal of Luminescence, 2015
Single crystals of Li 2 B 4 O 7 (LTB) with varying Ag content were grown using the Czochralski te... more Single crystals of Li 2 B 4 O 7 (LTB) with varying Ag content were grown using the Czochralski technique and studied for their optical absorption, photo-luminescence (PL) and thermally stimulated luminescence (TSL) properties. The optimum Ag concentration in the LTB was found to be about 500 ppm for the best TSL properties. A TSL readout setup has been described that uses a solar blind photo-multiplier tube (PMT) to match the emission from Ag which is in the UV region (peak at 270 nm). This has significantly improved the performance of the TSL setup by lowering dark counts and enhancing the signal due to a better matching between the emission from Ag ions and PMT response. In addition, the use of the solar blind PMT also minimized the thermal noise generated from heating of sample in the TSL setup. Radiation doses lower than 5 μGy could be measured using this setup with small LTB:Ag crystal samples (100 mg). The lower detection limit has been estimated to be 500 nGy.
physica status solidi (RRL) - Rapid Research Letters, 2015
ABSTRACT High quality lithium tetraborate; Li2B4O7 (LTB) single crystals with varying concentrati... more ABSTRACT 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.
Journal of Luminescence, 2015
The optically transparent ceramics (OTC) of CaF 2 :Mn were fabricated by a vacuum hot-press metho... more The optically transparent ceramics (OTC) of CaF 2 :Mn were fabricated by a vacuum hot-press method. Photo-luminescence (PL) and radio-luminescence measurements were carried out on CaF 2 :Mn OTCs to study the effect of processing on the luminescence properties of the material. The temperature dependence of PL and decay kinetics were investigated down to 77 K. The results were compared with the reported luminescence properties of CaF 2 :Mn single crystals. The comparison shows that the luminescence is similar at room temperature, however, the evolution of luminescence with temperature and decay mechanism of Mn 2+ centers in OTC are quite different. A possible explanation for the differences in the luminescence properties of CaF 2 :Mn OTC has been proposed.
AIP Conference Proceedings, 2012
ABSTRACT Epitaxial films of 2 at.% Eu doped CaF2 have been grown on (111) plane of CaF2 by a low ... more ABSTRACT 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.
AIP Conference Proceedings, 2012
ABSTRACT Nano-particles of CaF2: Mn were synthesized by a co-precipitation method. Optically tran... more ABSTRACT 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.
AIP Conference Proceedings, 2014
ABSTRACT Partially transparent ceramic of 2 at.% Eu doped CaF2 have been grown preferentially tow... more ABSTRACT Partially transparent ceramic of 2 at.% Eu doped CaF2 have been grown preferentially towards [111] direction. For this purpose, Eu doped CaF2 nanoparticles (size similar to 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 Temperature dependent photoluminescence (PL) spectroscopy has been employed to study the... more ABSTRACT 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.
AIP Conference Proceedings, 2012
ABSTRACT Thin films of thallium activated cesium iodide (CsI: Tl) have been deposited on silicon ... more ABSTRACT 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.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2012
An optically transparent ceramic of CaF 2 :Mn has been prepared by hot pressing of nano-phase pow... more An optically transparent ceramic of CaF 2 :Mn has been prepared by hot pressing of nano-phase powders under vacuum conditions. The transmission recorded for a 1 mm thick sample at 800 nm was about 50%. A scanning electron micrograph exhibited a pore-free structure without any secondary phases at the grain boundaries. The doping concentration of Mn and its oxidation state as determined using secondary ion mass spectrometry and X-ray photoemission spectroscopy were 1.5 at.% and Mn 2+ , respectively. The photo-luminescence properties of these ceramics were studied and their application as a thermo-luminescent dosimeter has been established. These ceramics were able to measure low level doses down to about 3 mGy and exhibited a linear output up to 100 mGy.
Journal of Luminescence, 2012
Journal of Luminescence, 2013
ABSTRACT Single crystals of Li2B4O7 (LTB) doped with Cu and Ag and Cu, Ag co-doped have been grow... more ABSTRACT Single crystals of Li2B4O7 (LTB) doped with Cu and Ag and Cu, Ag co-doped have been grown using the Czochralski technique. Luminescence studies revealed a sensitizer role of Ag in the LTB:Cu,Ag crystal. It is found that, despite an energy transfer from Ag+ to Cu+ centers, emission from both the centers participate in the thermally stimulated luminescence (TSL) of co-doped. We propose that the LTB:Cu,Ag crystal will be a better and efficient material for dosimeters [TSL as well as optically stimulated luminescence (OSL)] compared to singly doped LTB crystals in a photo-readout system having a maximum response in the 200 nm to 600 nm range.
An optically transparent ceramic of CaF 2 :Mn has been prepared by hot pressing of nano-phase pow... more An optically transparent ceramic of CaF 2 :Mn has been prepared by hot pressing of nano-phase powders under vacuum conditions. The transmission recorded for a 1 mm thick sample at 800 nm was about 50%. A scanning electron micrograph exhibited a pore-free structure without any secondary phases at the grain boundaries. The doping concentration of Mn and its oxidation state as determined using secondary ion mass spectrometry and X-ray photoemission spectroscopy were 1.5 at.% and Mn 2+ , respectively. The photo-luminescence properties of these ceramics were studied and their application as a thermo-luminescent dosimeter has been established. These ceramics were able to measure low level doses down to about 3 mGy and exhibited a linear output up to 100 mGy.
UV excited photo luminescence from Li 2 B 4 O 7 :Cu and Li 2 B 4 O 7 :Cu, Ag single crystals has ... more UV excited photo luminescence from Li 2 B 4 O 7 :Cu and Li 2 B 4 O 7 :Cu, Ag single crystals has been investigated in the temperature range from 77 K to 300 K. An excitation band having a doublet structure at 240 nm and 262 nm was observed for the emission at 370 nm that corresponds to 1 A 1g-1 E g and 1 A 1g-1 T 2g crystal field components of the 3d 10-3d 9 4s 1 transition of Cu þ. The relative intensity of these components and their temperature dependence provide a measure of the off-center displacement of the Cu þ ground state in the crystal lattice site. The co-doped Ag plays a role of a sensitizer when doped with Cu and increases the overall emission as the emission between Ag states lies in the excitation region of Cu states. The 370 nm emission in both the crystals slightly decreases with temperature; however a sudden increase in the intensity around 264 K was observed.
Li 2 B 4 O 7 :Ag single crystals are grown by the Czochralski technique. Li 2 B 4 O 7 :Ag single ... more Li 2 B 4 O 7 :Ag single crystals are grown by the Czochralski technique. Li 2 B 4 O 7 :Ag single crystals are investigated using TSL, OSL techniques. These crystals are found promising for OSL dosimetry.
Nuclear Instruments and …, Jan 1, 2006
AIP Conference Proceedings, 2012
ABSTRACT High optical quality Li2B4O7 (LTB) single crystals and glassy phases of pure, doped (Cu,... more ABSTRACT 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.
Journal of Luminescence, 2015
Single crystals of Li 2 B 4 O 7 (LTB) with varying Ag content were grown using the Czochralski te... more Single crystals of Li 2 B 4 O 7 (LTB) with varying Ag content were grown using the Czochralski technique and studied for their optical absorption, photo-luminescence (PL) and thermally stimulated luminescence (TSL) properties. The optimum Ag concentration in the LTB was found to be about 500 ppm for the best TSL properties. A TSL readout setup has been described that uses a solar blind photo-multiplier tube (PMT) to match the emission from Ag which is in the UV region (peak at 270 nm). This has significantly improved the performance of the TSL setup by lowering dark counts and enhancing the signal due to a better matching between the emission from Ag ions and PMT response. In addition, the use of the solar blind PMT also minimized the thermal noise generated from heating of sample in the TSL setup. Radiation doses lower than 5 μGy could be measured using this setup with small LTB:Ag crystal samples (100 mg). The lower detection limit has been estimated to be 500 nGy.
physica status solidi (RRL) - Rapid Research Letters, 2015
ABSTRACT High quality lithium tetraborate; Li2B4O7 (LTB) single crystals with varying concentrati... more ABSTRACT 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.
Journal of Luminescence, 2015
The optically transparent ceramics (OTC) of CaF 2 :Mn were fabricated by a vacuum hot-press metho... more The optically transparent ceramics (OTC) of CaF 2 :Mn were fabricated by a vacuum hot-press method. Photo-luminescence (PL) and radio-luminescence measurements were carried out on CaF 2 :Mn OTCs to study the effect of processing on the luminescence properties of the material. The temperature dependence of PL and decay kinetics were investigated down to 77 K. The results were compared with the reported luminescence properties of CaF 2 :Mn single crystals. The comparison shows that the luminescence is similar at room temperature, however, the evolution of luminescence with temperature and decay mechanism of Mn 2+ centers in OTC are quite different. A possible explanation for the differences in the luminescence properties of CaF 2 :Mn OTC has been proposed.
AIP Conference Proceedings, 2012
ABSTRACT Epitaxial films of 2 at.% Eu doped CaF2 have been grown on (111) plane of CaF2 by a low ... more ABSTRACT 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.
AIP Conference Proceedings, 2012
ABSTRACT Nano-particles of CaF2: Mn were synthesized by a co-precipitation method. Optically tran... more ABSTRACT 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.
AIP Conference Proceedings, 2014
ABSTRACT Partially transparent ceramic of 2 at.% Eu doped CaF2 have been grown preferentially tow... more ABSTRACT Partially transparent ceramic of 2 at.% Eu doped CaF2 have been grown preferentially towards [111] direction. For this purpose, Eu doped CaF2 nanoparticles (size similar to 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 Temperature dependent photoluminescence (PL) spectroscopy has been employed to study the... more ABSTRACT 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.
AIP Conference Proceedings, 2012
ABSTRACT Thin films of thallium activated cesium iodide (CsI: Tl) have been deposited on silicon ... more ABSTRACT 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.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2012
An optically transparent ceramic of CaF 2 :Mn has been prepared by hot pressing of nano-phase pow... more An optically transparent ceramic of CaF 2 :Mn has been prepared by hot pressing of nano-phase powders under vacuum conditions. The transmission recorded for a 1 mm thick sample at 800 nm was about 50%. A scanning electron micrograph exhibited a pore-free structure without any secondary phases at the grain boundaries. The doping concentration of Mn and its oxidation state as determined using secondary ion mass spectrometry and X-ray photoemission spectroscopy were 1.5 at.% and Mn 2+ , respectively. The photo-luminescence properties of these ceramics were studied and their application as a thermo-luminescent dosimeter has been established. These ceramics were able to measure low level doses down to about 3 mGy and exhibited a linear output up to 100 mGy.
Journal of Luminescence, 2012
Journal of Luminescence, 2013
ABSTRACT Single crystals of Li2B4O7 (LTB) doped with Cu and Ag and Cu, Ag co-doped have been grow... more ABSTRACT Single crystals of Li2B4O7 (LTB) doped with Cu and Ag and Cu, Ag co-doped have been grown using the Czochralski technique. Luminescence studies revealed a sensitizer role of Ag in the LTB:Cu,Ag crystal. It is found that, despite an energy transfer from Ag+ to Cu+ centers, emission from both the centers participate in the thermally stimulated luminescence (TSL) of co-doped. We propose that the LTB:Cu,Ag crystal will be a better and efficient material for dosimeters [TSL as well as optically stimulated luminescence (OSL)] compared to singly doped LTB crystals in a photo-readout system having a maximum response in the 200 nm to 600 nm range.
An optically transparent ceramic of CaF 2 :Mn has been prepared by hot pressing of nano-phase pow... more An optically transparent ceramic of CaF 2 :Mn has been prepared by hot pressing of nano-phase powders under vacuum conditions. The transmission recorded for a 1 mm thick sample at 800 nm was about 50%. A scanning electron micrograph exhibited a pore-free structure without any secondary phases at the grain boundaries. The doping concentration of Mn and its oxidation state as determined using secondary ion mass spectrometry and X-ray photoemission spectroscopy were 1.5 at.% and Mn 2+ , respectively. The photo-luminescence properties of these ceramics were studied and their application as a thermo-luminescent dosimeter has been established. These ceramics were able to measure low level doses down to about 3 mGy and exhibited a linear output up to 100 mGy.
UV excited photo luminescence from Li 2 B 4 O 7 :Cu and Li 2 B 4 O 7 :Cu, Ag single crystals has ... more UV excited photo luminescence from Li 2 B 4 O 7 :Cu and Li 2 B 4 O 7 :Cu, Ag single crystals has been investigated in the temperature range from 77 K to 300 K. An excitation band having a doublet structure at 240 nm and 262 nm was observed for the emission at 370 nm that corresponds to 1 A 1g-1 E g and 1 A 1g-1 T 2g crystal field components of the 3d 10-3d 9 4s 1 transition of Cu þ. The relative intensity of these components and their temperature dependence provide a measure of the off-center displacement of the Cu þ ground state in the crystal lattice site. The co-doped Ag plays a role of a sensitizer when doped with Cu and increases the overall emission as the emission between Ag states lies in the excitation region of Cu states. The 370 nm emission in both the crystals slightly decreases with temperature; however a sudden increase in the intensity around 264 K was observed.
Li 2 B 4 O 7 :Ag single crystals are grown by the Czochralski technique. Li 2 B 4 O 7 :Ag single ... more Li 2 B 4 O 7 :Ag single crystals are grown by the Czochralski technique. Li 2 B 4 O 7 :Ag single crystals are investigated using TSL, OSL techniques. These crystals are found promising for OSL dosimetry.
Nuclear Instruments and …, Jan 1, 2006