Luminescent Properties of Praseodymium in CaWO4 Matrix


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Praseodymium (Pr3+) with rich f energy levels can generate various visible emissions, but the luminescence of Pr3+ in a CaWO4 matrix has not yet been studied. In this article, the phosphors of Pr3+-doped CaWO4 were synthesized via a high temperature solid-state reaction, and the photoluminescence (PL) and afterglow properties of Pr3+ in the CaWO4 matrix were investigated. The phase identifications of the samples show that an impure monoclinic phase appears when the Pr3+ concentration is high. The results of PL exhibit the usual Pr3+ characteristic emissions as well as an emission that is produced by the charge transfer from 5d of W6+ to 2p of O2− under a shortwave ultraviolet excitation. An intermediate energy transfer occurs during the charge transfer which induces the afterglow. The quenching point of Pr3+ in CaWO4 is 2 mol%, corresponding to the critical energy transfer distance of ~20 Å. The quenching mechanism in the Pr3+-doped CaWO4 is the dipole-dipole interaction. The Ca2+ vacancies (VCa) are the defects that induce the traps and capture holes from O2−. The thermal energy of holes liberation from VCa to O2− results in the charge transfer accompanied by an energy transfer to Pr3+, and consequently generates the afterglow. The experimental results also show that the afterglow characteristics of Pr3+ are prolonged by incorporating Pr3+ in the CaWO4 matrix.