From surface to lattice: structural insights and luminescence tuning of biocompatible SnO2:Eu3+ ultrasmall nanoparticles

Tin oxide (SnO₂) is a critical n-type semiconductor with applications including transparent conducting electrodes, chemical sensors, and photocatalysts. However, the location of the aliovalent dopant in SnO₂ nanoparticles remains to be clarified. Herein, we report the synthesis, characterization, and optical investigation of SnO₂:Eu³⁺ nanoparticles obtained via the coprecipitation method. A systematic study was carried out for SnO₂:Eu³⁺ (0.5 mol%), by varying the thermal treatment temperature at 100 °C, 400 °C, 700 °C, and 1000 ºC. These materials were characterized by FTIR spectroscopy, TGA, XRD, SEM-EDS, TEM, DRS - UV/VIS and photoluminescence spectroscopy. In vitro cytotoxicity assays using NIH/3T3 murine fibroblasts demonstrated cell viability above 80% at concentrations up to 500 μg/mL, classifying the USNPs as safe for biological use. These findings highlight the potential of SnO₂:Eu³⁺ USNPs as robust, structurally tunable, and biocompatible nanoprobes.