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Highlights: [•] Ag–SnO2 composite powders were synthesized by the sol–gel auto-combustion method. [•] Citric acid facilitates sol formation and reduces particle agglomeration. [•] SnO2 nanoparticles disperse homogenously in the Ag matrix. [•] Citric acid improves microstructure and properties of the Ag-SnO2 composite. [ABSTRACT FROM AUTHOR]

Perovskite-type microspheres of LaAlO 3 : x Mn4+, y Ge4+ have been fabricated through thermal decomposition of the amorphous precursors autoclaved from the nitrates and ethylene glycol in the prescence of citric acid. LaAlO 3 : x Mn4+ 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 LaAlO 3 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 [Mn Al defects. Doping Ge4+ does not significantly change the morphology, crystal structure, band gap, and thermal stability of LaAlO 3 :Mn4+ sample, but it induces stronger asymmetry of MnO 6 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 [Ge Al 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. Image 1 • Perovskite-type microspheres of LaAlO 3 :Mn4+/Ge4+ were originally synthesized. • Doping Ge4+induced a greatly enhanced NIR emission intensity by 260%. • Incorporation of Ge4+ gave rise to the improved persistent luminescence. • The spheres exhibited repeated illumination by heating without light source. [ABSTRACT FROM AUTHOR]