Near-infrared emitting microspheres of LaAlO3:Mn4+: Defects engineering via Ge4+ doping for greatly enhanced luminescence and improved afterglow

Abstract Perovskite-type microspheres of LaAlO3:xMn4+,yGe4+ have been fabricated through thermal decomposition of the amorphous precursors autoclaved from the nitrates and ethylene glycol in the prescence of citric acid. LaAlO3:xMn4+ spheres emit broad and bright near infrared (NIR) emission ranging from 680 nm to 750 nm with the maximum at around 730 nm. The quenching concentration for Mn4+ in LaAlO3 is found at x = 0.1%. In the absence of light source, the spheres emit intense NIR afterglow for 10 min at room temperature, mainly due to the formation of [MnAl] defects. Doping Ge4+ does not significantly change the morphology, crystal structure, band gap, and thermal stability of LaAlO3:Mn4+ sample, but it induces stronger asymmetry of MnO6 and more isolated Mn4+ ions, which thus contributes to greatly enhanced NIR emission intensity by 260%. Ge4+ ions occupying Al site leads to the formation of positive [GeAl] defects, which are closely related to the trap concentration rather than the trap depth. Incorporation of Ge4+ gives rise to the improved persistent luminescence, and the most intense afterglow is found at y = 0.6%. The spheres exhibit repeatable afterglow by a proper heat processing in the absence of light source, indicating their potential application in optical data storage.