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In this work, the Stokes and anti-Stokes luminescence (upconversion) of erbium in powders of yttrium-aluminum garnet with various concentrations of erbium, as well as co-doped with erbium and ytterbium, synthesized by the sol-gel method using multistage thermal processing, was investigated. It was established that the phase composition of the resulting powders corresponds to the crystal structure of garnet. For all powders, high-intensity Stokes luminescence with a maximum at 1.53 μm was observed due to the I_13/24→I_15/24 electronic transition, and anti-Stokes luminescence was observed with the most intense band in the region of 0.65–0.69 μm, associated with the F_9/24→I_15/24 transition of Er^3+ ions. The highest intensity of the Stokes luminescence is observed for the maximum substitution of yttrium by erbium considered here, which corresponds to the Yb_1.5Er_1.5Al_5O_12 stoichiometry. The highest intensity of the anti-Stokes luminescence is for the lowest erbium concentration and for codoping with ytterbium with Y_2.71Er_0.29Al_5O_12 and Y_2Er_0.5Yb_0.5Al_5O_12 stoichiometries, respectively.

Erbium-doped barium titanate (BaTiO3:Er) xerogel film with a thickness of about 500 nm was formed on the porous strontium titanate (SrTiO3)xerogel film on Si substrate after annealing at 800∘C or 900∘C. The elaborated structures show room temperature upconversion luminescence under 980 nm excitation with the photoluminescence (PL) bands at 523, 546, 658, 800 and 830 nm corresponding to 2H11/2→4I15/2, 4S3/2→4I15/2, 4F9/2→4I15/2and 4I9/2→4I15/2transitions of trivalent erbium. Raman and X-ray diffraction (XRD) analysis of BaTiO3:Er\porous SrTiO3\Si structure showed the presence of perovskite phases. Its excellent up-conversion optical performance will greatly broaden its applications in perovskite solar cells and high-end anti-counterfeiting technologies.