Luminescent Properties of Praseodymium in CaWO4 Matrix

Praseodymium (Pr 3+ ) with rich f energy levels can generate various visible emissions, but the luminescence of Pr 3+ in a CaWO 4 matrix has not yet been studied. In this article, the phosphors of Pr 3+ -doped CaWO 4 were synthesized via a high temperature solid-state reaction, and the photoluminescence (PL) and afterglow properties of Pr 3+ in the CaWO 4 matrix were investigated. The phase identifications of the samples show that an impure monoclinic phase appears when the Pr 3+ concentration is high. The results of PL exhibit the usual Pr 3+ characteristic emissions as well as an emission that is produced by the charge transfer from 5 d of W 6+ to 2 p of O 2− under a shortwave ultraviolet excitation. An intermediate energy transfer occurs during the charge transfer which induces the afterglow. The quenching point of Pr 3+ in CaWO 4 is 2 mol%, corresponding to the critical energy transfer distance of ~20 Å. The quenching mechanism in the Pr 3+ -doped CaWO 4 is the dipole-dipole interaction. The Ca 2+ vacancies ( V Ca ) are the defects that induce the traps and capture holes from O 2− . The thermal energy of holes liberation from V Ca to O 2− results in the charge transfer accompanied by an energy transfer to Pr 3+ , and consequently generates the afterglow. The experimental results also show that the afterglow characteristics of Pr 3+ are prolonged by incorporating Pr 3+ in the CaWO 4 matrix.