Computational and experimental study on undoped and Er-doped lithium tantalate nanofluorescent probes

We present a combined density functional theory (DFT) and experimental work on lithium tantalate LiTaO₃ (LT) and its Er-doped counterparts. We calculate the electronic and optical properties for both LT and LT:Er⁺³, with Er occupying either Li or Ta sites, at 4.167 mol%. The generalized gradient approximation (GGA) calculations show that the Er-4 f bands appear closer to the conduction band bottom and to the valance band top, for the first and second doped configurations, respectively. This agrees with changes in the imaginary part of the frequency dependent dielectric function between the doped configurations. There are striking differences between the GGA and the hybrid functional HSE06 calculations for the band structures of the doped configurations. HSE06 accurately predicts the location in energy for all Er-4 f orbitals: These are now spread in energy and appear above and below the Fermi energy. We synthesized LT:Er⁺³ nanoparticles, validated through X-ray diffraction and Scanning Electron Microscopy. Differential scanning calorimetry and thermogravimetric analysis confirmed increases in the activation energy and lowering of the reaction temperature due to Er⁺³ doping. The LT:Er⁺³photoluminescence showed strong f–f emission in the visible and near-infrared regions, in an excellent agreement with the HSE06 electronic information.