Red and near-infrared emitting phosphors based on Eu 3+ - or Nd 3+ -doped lanthanum niobates prepared by the sol-gel route.

We have evaluated the structural and luminescence properties of Eu 3+ - or Nd 3+ -doped lanthanum niobate systems synthesized via a sol-gel route and containing different dopant contents. XRD analysis revealed that the orthorhombic La 3 NbO 7 and monoclinic LaNbO 4 crystalline phases were present in all the samples, regardless of the dopant concentration. The excitation spectra of the samples displayed a broad band due to Nb 5+ →O 2- charge transfer; this band was quite sensitive to the increasing Eu 3+ content. The photoluminescence emission spectra of the samples with a lower Eu 3+ content showed that Eu 3+ occupied both crystalline phases. However, when the Eu 3+ content increased, these ions preferentially occupied the C 2 symmetry sites in the LaNbO 4 host lattice. There was no emission quenching for the Eu 3+ -doped samples with a Eu 3+ content as high as 20 mol%. The emission spectra of the Nd 3+ -doped samples displayed an intense emission band in the NIR-II biological window under NIR-I excitation, at 808 nm. In the case of the samples with a lower Nd 3+ content, Nd 3+ occupied distinct symmetry sites in La 3 NbO 7 . In contrast, in the samples with a higher Nd 3+ content, these ions preferentially occupied LaNbO 4 sites. The Nd 3+ concentration that quenched emission in the Nd 3+ -doped samples was about 2.6 mol%, due to Nd 3+ -Nd 3+ cross-relaxation processes. On the basis of these findings, the Eu 3+ -doped samples explored herein have promising applications in the lighting field, whereas the Nd 3+ -doped samples have potential use as solid-state lasers and biomarkers.