Effect of Redox Reaction Products on the Luminescence Switching Behavior in CePO₄:Tb Nanorods

The luminescence switching behavior of CePO 4:Tb has been widely studied upon an interfacial oxidation–reduction reaction where KMnO 4 and ascorbic acid act as an oxidant and a reductant, respectively. However, the transformation of Mn-involved species derived from KMnO 4 during the oxidation–reduction cycle and their effect on the luminescence properties of CePO 4:Tb have not been explored so far. Here, we further study this interfacial reaction between CePO 4:Tb and KMnO 4 through various characterization techniques, such as X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. We find that an amorphous manganese oxide layer forms on the CePO 4:Tb surface along with the partial oxidation of Ce(III) upon addition of KMnO 4 . In the subsequent reduction, the ascorbic acid not only reduces Ce(IV) to Ce(III) but also dissolves the formed manganese oxide. If manganese oxide is kept on the CePO 4:Tb surface during the reduction treatment, the photoluminescence of Tb(III), due to the energy transfer from Ce(III) to Tb(III), would be restrained even if Ce(IV) ions were efficiently reduced. Although the degree of surface oxidation/reduction (Ce(III)/Ce(IV)) was considered to be a key factor for the luminescence quenching/recovery behavior in previous studies, there is a strong indication that the reaction product, e.g. manganese oxide, and associated surface defects generated from the oxidation–reduction reaction can disturb the photoluminescence of Tb(III) when they are not removed.