Impregnation of Ce<sup>3+</sup> in YPO<sub>4</sub> Lattice for Enhanced Green Emission for Biomedical Applications

Green light-emitting YPO 4 :Tb 3+ and YPO 4 :Tb 3+ : Ce 3+ nanoparticles were synthesised at low temperatures using the polyol method. The phase purity, micromorphology and luminescence characteristics were studied using Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier Transfer Infrared absorption spectroscopy (FT-IR) and Photoluminescence spectroscopy (PL). Combined XRD and TEM analysis showed that the YPO 4 nanoparticles crystallised into a single phase of tetragonal (I41/amd) structure. For all samples, the emission intensity at λ em =543 nm assigned to 5 D 4 → 7 F 5 is more prominent than 5 D 4 → 7 F 6 with a maximum at λ em =488 nm, and the asymmetric ratio was calculated and analysed. The asymmetric ratio is strongly correlated with the symmetry around the local environment of Tb 3+ ions. A significant increase in the asymmetric ratio is observed with an increase in annealing temperature. The energy transfer from Ce 3+ ions to Tb 3+ ions was tested by studying the photoluminescence properties of YPO 4 :Tb 3+ and YPO 4 :Tb 3+ : Ce 3+ nanoparticles and how it results in the improvement of the luminescence intensity. The Ce 3+ 5d−4f and Tb 3+ 5 D 4 → 7 F J ( J = 6 − 3) transitions were observed.