Thermoluminescence glow curve study of UV-irradiated Mn4+doped zinc aluminate spinel nanophosphor

Abstract

This paper is focused on thermoluminescence study of Mn⁴⁺-doped zinc aluminate nanophosphor with different Mn concentrations (0.5–3 mol %). The samples were chemically synthesized via microwave combustion method and annealed at 900 °C temperature. Nanoregime, single-phase spinel structure formation was confirmed by XRD and further analysed by Rietveld refinement method. The photoluminescence (PL) spectrum and PL decay curve revealed 745 nm emission under ultraviolet excitation wavelength, and afterglow decay time of the order of milliseconds. The thermoluminescence (TL) response was carried out using UV irradiation (254 nm) with different exposure time intervals. The effect of Mn concentration (0.5–3 mol %) and UV exposure time on TL glow curve of zinc aluminate was presented and discussed. A broad TL peak with 40 min UV irradiation exposure time was observed. Progression in TL intensity was observed with Mn concentration from 0.5 to 2% and above 2 mol %, and TL intensity was quenched. Also, a noticeable TL peak shifting was found for higher Mn⁴⁺ ions concentration. The optimum TL peak corresponding to 40 min exposure time (for 2 mol % Mn) was deconvoluted into two peaks at 395 K and 422 K temperature. The prepared ZnAl₂O₄:Mn⁴⁺ (2 mol %) nanophosphor showed linear dose response, essential property of dosimeters. The assessment of trap creation and trap depth was analysed by calculating the trap parameters. Two different methods, computerized glow curve deconvolution (CGCD) and Chen’s peak shape (CPS) method, were applied to calculate various kinetic TL parameters, e.g. order of kinetics (b), trap depth (activation energy E_av), and frequency factor (S). The measured trap depth suggested the involvement of shallow trap states for recombination process. This study will be immensely helpful in understanding the thermoluminescence behaviour of Mn⁴⁺-doped zinc aluminate nanophosphor for UV-TLD applications.