Insight into the optical absorption and luminescent properties due to the presence of Pr4+ in Pr-doped Y2O3

Powder samples of undoped and Pr-doped Y2O3 are synthesized by the reverse precipitation method and annealed at 1000 °C for 1 h. X-ray diffraction patterns confirm the presence of the well-known Y2O3 cubic phase. The optical properties of the compounds are characterized by diffuse reflectance and photoluminescence spectroscopies. The presence of a huge absorption band in the Pr-doped samples is attributed to the presence of Pr4+, but also emission and excitation luminescent spectra reveal the existence of Pr3+. To explain the origin of the broad absorption band, it is made use of an approach formulated decades ago based on the assumption that ligand-to-metal charge transfer states O2−/- → Pr4+/3+ are involved. To implement this approach, a deconvolution of the absorption spectrum, following a judicious conjecture based on phenomenological methods in which each deconvolution's component is associated with a transition from the top of the valence band, mainly O-2p in character, to each of the Pr3+ f-f states, or from the Pr3+-3H4 ground state to one of its d states, is performed. Our results match consistently with those energies calculated from a vacuum referred binding energy diagram, allowing to rationalize the presence of a huge absorption band as well as to explain the absence of the emission coming from the most energetic Pr3+ electronic transitions when Pr4+ is present in Pr-doped Y2O3.