U. Madhusoodanan

Thermoluminescence mechanism in rare-earth-doped magnesium tetra borate phosphors

Magnesium tetra borate (MTB) doped with rare earths (REs) was prepared by the solid state sintering technique. Among the different RE dopants studied in this phosphor, gadolinium-doped phosphors resulted in a dosimetric peak at a relatively higher temperature. The thermoluminescence (TL) emission spectra of RE-doped MTB showed characteristic RE 3+ emissions. Electron paramagnetic resonance measurements were carried out in these phosphors to identify the defect centers formed during gamma irradiation and to establish a mechanism for the TL process. Signals corresponding to (BO 3)2−, O v− were seen upon irradiation which vanished on annealing at 250 °C, showing the role of these centers in the TL process. The thermal activation energies calculated based on the decay of these signals matched well with those calculated on the basis of the usual conventional method showing the validity of the mechanism of TL.

Influence of (group IIB) codopants on the thermostimulated luminescence sensitivity of CaSO4:Dy/Tm

Thermostimulated luminescence (TSL) phosphors based on CaSO4:Dy, Zn and CaSO4:Tm, Cd have been studied. These phosphors show an increase in the 220 °C TSL peak intensity by a factor of about 50% compared to CaSO4:Dy, as there is no change in the position of the peak temperature. Their dose response characteristics to 60Co gamma radiation is similar to that of CaSO4:Dy. However, there are very minor changes in their photoluminescence intensity and excitation spectra compared with those of CaSO4:Dy.

Radiation-induced defects in manganese-doped lithium tetraborate phosphor

Lithium tetraborate doped with manganese synthesised by solid-state sintering technique exhibits a dosimetric peak at 280°C. The high-temperature glow curve results in no fading for three months. The sensitivity of Li2B4O7:Mn is determined to be 0.9 times that of TLD-100. The infrared spectrum of this phosphor indicates the presence of bond vibrations corresponding to BO4 tetrahedral and BO3 triangles. The mechanism for thermoluminescence in this phosphor was proposed based on the thermoluminescence (TL) emission spectra, kinetic analysis of TL glow curves and electron paramagnetic resonance (EPR) measurements on non-irradiated and gamma-irradiated phosphors. It was identified that oxygen vacancies and Boron oxygen hole centre (BOHC) are the electron and hole trap centres for TL in this phosphor. When the phosphor is heated, the electrons are released from the electron trap and recombine with the trapped holes. The excitation energy during the recombination is transferred to the nearby Mn(2+) ions, which emit light at 580 nm.

Thermostimulated luminescence in CaSO4 : Ag,Tm : Irradiation and storage temperature dependence

Abstract A new high sensitive thermostimulated luminescence phosphor CaSO4: Ag, Tm has been developed with a major peak around 330°C (603 K). The use of this material for measuring radiation dose during irradiation at different temperatures is investigated. It shows negligible change in sensitivity in the irradiation temperature range 100–550 K and about 20% fading at 575 K for a 10 min X-ray irradiation duration. The post-irradiation storage studies at different temperatures indicate that this phosphor is very stable even when stored at 523 K for 6 h after γ-irradiation at room temperature which makes it a good material for high temperature dosimetry applications.