Up-conversion emission and in vitro cytotoxicity characterization of blue emitting, biocompatible SrTiO3 nanoparticles activated with Tm3+ and Yb3+ ions

Functional SrTiO3 nanoparticles activated with a broad concentration range of Tm3+ and Yb3+ ions were obtained utilizing the citric route. The effect of the sintering temperature and optically active co-dopant concentration on the structural and up-conversion emission properties was studied by using XRD (X-ray powder diffraction) and spectroscopic techniques (emission, power dependence, emission kinetics). The particle size was verified by the TEM technique being in the range of 20-90 nm depending on the annealing temperature. It was shown that cross-relaxations contribute to depopulation of both (1)G(4) and H-3(4) levels, whereas some of them populate the H-3(4) level. These processes are strongly dependent on the concentration of Tm3+ and are responsible for the specific interplay between blue and NIR emissions. Extraordinary short decays were recorded due to the relatively high concentrations of rare earths, structural features of the host matrix, extended surface area and contribution of the non-radiative processes. The cytotoxic activity of the nanoparticles to J774.E murine macrophages and U2OS human osteosarcoma cells was assessed showing that SrTiO3:Tm3+/Yb3+ nanoparticles are biocompatible and can be potentially used in further bio-related applications such as active implant layers or injectable medical cement ingredients.