Effect of thermal treatment on luminescence properties of long persistent CaAl2O4:Eu2+,Dy3+ synthesized by combustion method

Abstract

We report on the effect of thermal treatments on photoluminescence, thermoluminescence and afterglow of CaAl2O4:Eu2+,Dy3+ synthesized by combustion method and annealed under a carbon atmosphere at 1423 K for 6 h. As synthetized phosphor exhibit a typical Eu2+ emission with a maximum at 438 nm corresponding to the allowed transition from 4f65d to 4f7 levels of Eu2+ ion. The TL glow curves recorded after beta irradiation consist of at least three overlapped TL peaks with maxima at about 340, 410, and 480 K and a high temperature TL with a peak maximum higher than 680 K. Immediately after beta irradiation, intense AG is observed demonstrating the possibility to emit lightfor hours at a level exceeding background signal. The decay curves exhibit two components, fast and slow, due to the liberation of electrons from traps responsible for the 340 and 410 TL peaks with characteristic duration times of about ten seconds and a couple of hours, respectively.The synthesized phosphor was subjected to additional thermal treatments (TTs) in an air atmosphere at 883 and 1183 K for 1h. The TTs lead to a pronounced increase the narrow excitation and emission bands attributable to f – f transitions of the Eu3+ ions and slight changes of the excitation and emission bands corresponding to Eu2+ ions. The effect the TTs on the TL reveals itself in the decrease of the 410 and 480 K TL peaks. On the other hand, the 340 K TL peak does not change under the TTs. The study of TT effects on luminescent properties of calcium aluminate codoped with rare earth is important for understanding the mechanism of trapping and detrapping processes in this phosphor.