Quantitative luminescence switching in CePO₄:Tb by redox reactions

Luminescence-switching behaviors of CePO₄:Tb³⁺ upon redox reactions were examined using KMnO₄ and l(+)-ascorbic acid as an oxidant and a reductant, respectively. Powdery nanorod-like CePO ₄:Tb³⁺ particles were synthesized by liquid-phase reactions of rare-earth ions and phosphate ions in aqueous solutions at low temperatures. According to X-ray diffractometry, X-ray photoelectron spectroscopy, and transmission electron microscopy, the oxidizing treatment of CePO₄:Tb³⁺ was found to bring about partial oxidation of Ce³⁺ to Ce⁴⁺ and a small degree of structural damage in the particle surface, which could be recovered by the subsequent reducing treatment. Photoluminescence (PL) intensity of CePO₄:Tb³⁺ due to ⁵D₄ → ⁷F_J (J = 3-6) electronic transitions of Tb³⁺ was decreased with increasing KMnO₄ concentration in an exponential manner, resulting from excitation cutoff by an intervalence Ce³⁺ → Ce⁴⁺ charge transfer and emission cutoff by a Ce³⁺ absorption red-shifted to the visible region. Reversely, PL intensity was increased also in the exponential manner by increasing the l(+)-ascorbic acid concentration in reducing the previously oxidized CePO₄:Tb³⁺, thereby achieving the quantitative, repetitive luminescence switching. Our results demonstrate that the luminescence switching is regarded as a surface phenomenon without a whole change of structure and valence in the CePO₄:Tb ³⁺ material.