Intra- and inter-configurational luminescence spectroscopy of Pr3+ -doped YPO4 nanophosphors

Nanopowders of YPO₄ phosphors with different Pr³⁺doping were successfully prepared by a sol gel method under different synthesis conditions. The crystallite size and strain show a strong dependence on the Pr³⁺ doping concentration and on the annealing temperature. By annealing at 300 °C one can obtain the xenotime structure of the pure YPO₄. The crystallite size can be controlled by controlling the annealing temperature and it increases with increasing the annealing temperature. The room temperature inter-configurational 4f² ↔ 4f5d and intra-configurational 4f²↔ 4f² emission-excitation transitions spectra are measured and investigated. Upon 4f² → 4f5d excitation transition, all the samples present broad intense emission bands attributed to 4f5d → 4f² emission transitions and peaks in red region assigned to ¹D₂→³H₄ transition as photon cascade emission phenomena (PCE). The presence of only ¹D₂→³H₄ transition is discussed. In addition, the ¹D₂ energy level lifetimes as well as the refractive indexes were determined and discussed.