Microscopic and optical parameters of Eu³⁺-doped SnO₂–SiO₂ nanocomposites prepared by sol−gel method

We investigate the excitation routes for the red photo-emission in Eu−doped SnO₂–SiO₂ nanocomposites prepared by sol–gel method. Single phase tetragonal rutile structure of SnO₂ is formed in the system at different annealing temperatures from 850 °C to 1150 °C. Intense Eu³⁺ ion photoluminescence (PL) spectra consist of a series of resolved emission bands in the range from 570 nm to 645 nm. These emission bands are assigned to the radiative recombinations within the intra-4f electronic core states of the Eu³⁺ ions. PL excitation spectra affirm direct and indirect excitation processes for the optically active Eu³⁺ ions. The indirect excitation occurring via the SnO₂ nanocrystals is more efficient than the direct excitation wherein Eu³⁺ ions are excited directly via the high excited states. PL decay dynamics revealed different incorporations of Eu³⁺ ions in the nanocomposites. The Judd−Ofelt is used to calculate some radiative parameters such as the luminescence quantum efficiency, gain bandwidth and optical gain. The intensity parameters show that the asymmetry of the coordination structure surrounding the Eu³⁺ ion and covalent of Eu³⁺−ligand bonding decrease with the increased SnO₂ content.