What makes the luminescence of Prdifferent in CaTiO3 and CaZrO3 ?

Although orthorhombic CaZrO₃ and CaTiO₃ perovskites are characterised by very similar structural features, they show different luminescence properties when doped with Pr³⁺ ions: the former exhibits the typical greenish-blue ³P₀→³H₄ emission, while the latter shows a single red ¹D₂→³H₄ luminescence. The explanation of this difference requires to understand the mechanism responsible for total quenching of ³P₀ emission in CaTiO₃ host. Among the different possible relaxation pathways from ³P₀ to ¹D₂, intersystem crossing through low lying 4f¹5d¹ levels has been proposed in a previous study. Owing to new spectroscopic results on CaZrO₃:Pr³⁺ and CaTiO₃:Pr³⁺, the role of the 4f5d band is reconsidered and an alternative relaxation channel is proposed via low lying intervalence charge transfer state.