The behavior of thermally and optically stimulated luminescence of SrAl₂ O₄: Eu^{2 +}, Dy^{3 +} long persistent phosphor after blue light illumination

The behavior of afterglow (AG), thermoluminescence (TL), infrared stimulated luminescence (IRSL) and phototransferred TL (PTTL) under thermal and/or infrared (IR) stimulation in blue (470 nm) light illuminated at room temperature (RT) SrAl₂ O₄ : Eu^{2 +}, Dy^{3 +} is presented. The TL glow curve consists of four peaks with maxima at about 340, 430, 560 and 680 K. The 340 and 440 K peaks are described well by second order kinetics with activation energies of 0.83 and 1.05 eV, respectively. The AG decay is fitted by the Becquerel's law with exponent 1.5 and correlates well with the thermal emptying of the traps responsible for the 340 K peak. The 340 and 430 K TL peak traps are destroyed under IR (830 nm) stimulation creating IRSL. IR stimulation after illumination with blue light and preliminary heating restore partially the 340 and 430 K TL peaks by phototransfer from deeper traps. The shape of the IRSL decay curves depends strongly on the preheating temperature and is determined by simultaneous refilling of the 340 and 430 K TL traps and their reverse filling due to phototransfer from the deeper traps under IR stimulation. The obtained data are interpreted by the transformation of Eu^{2 +} and Dy^{3 +} to Eu^{3 +} and Dy^{2 +} under blue light illumination and their reverse transformation under thermal or IR stimulation. The Eu^{2 +} ions are the luminescent centers and the Dy^{2 +} centers are the IR sensitive traps responsible for the TL peaks, AG and IRSL.