Traplevel spectroscopic studies of BaCO3: Eu and BaCO3:241Am phosphors

Abstract

Abstract With a view to understanding the defects due to self-irradiation in 241Am (α-active with T ½=433 years) doped BaCO3 and their role in thermally induced free radical reactions/electron-hole recombination, trap level spectroscopic studies were conducted on BaCO3: 241Am and BaCO3: Eu (lanthanide analogue of Am) using Thermally Stimulated Luminescence (TSL) and Electron Spin Resonance (ESR) techniques. In the case of 241Am-doped BaCO3 phosphor, three glow peaks at 357, 420 and 500 K (for rate of heating β=2.5 K sec−1) were observed and their spectral character has shown that Am2+ acts as the luminescent centre. The TSL glow pattern and the ESR spectrum arising due to internal α-irradiation was unaltered with further (external) γ-irradiation of the phosphor. The ESR studies on these samples have shown that the carboxy CO2- radicals are produced due to α-irradiation and their thermal instabilities are responsible for triggering the processes responsible for the observed TSL peaks. In the γ-irradiated BaCO3: Eu phosphor, paramagnetic radical ions O2 - and CO3- were observed and the electron-hole recombination processes associated with their thermal destruction are identified as the mechanisms responsible for the thermally stimulated relaxation resulting in TSL at 383 and 430 K. It is observed that the pick-up of significant amounts of sodium impurity played an important role in the TSL processes. Sodium impurity helped the stabilisation of the (Na+-O2 −)-complex in BaCO3:Eu which was absent in BaCO3:241Am. This is consistent with the total absence of O2 − radical in 241Am-doped samples probably due to internal heating caused by α-decay.