化学的環境に応答する無機イメージングパウダーの創製

抄録

Inorganic phosphors that have luminescence switching function are expected to visualize changes in surrounding media. In this study, an attempt has been made to develop a novel phosphor based on CeO₂ with such function using its excellent redox responsibility. The Sm³⁺ ion has been chosen as a dopant in CeO₂ because it shows a relatively strong visible emission due to allowed magnetic-dipole transitions in a cubic CeO₂ host. Since the redox responsibility was thought to depend largely on the structure of CeO₂:Sm³⁺ particles, three kinds of synthetic methods have been employed, namely, the solid-state reaction, the spray drying, and the hydrothermal method, to obtain samples of different microstructures. The sample from the solid-state reaction was composed of micrometer-sized particles and it showed very poor luminescence switching function. On the other hand, the sample from the spray drying was a nano-sized powder and exhibited luminescence quenching in response to Ce⁴⁺→Ce³⁺ reduction by an aqueous L(+)-ascorbic acid solution at room temperature. The samples from the hydrothermal reaction had three kinds of morphologies as cube-like, sphere-like, and rod-like nanoparticles. The luminescence quenching behavior also depended on such the morphologies and only the rod-like sample showed appreciable quenching. The reduced rod-like sample could be oxidized by H₂O₂, followed by luminescence recovery. Thus the CeO₂:Sm³⁺ phosphor has been proven to have luminescence switching function, depending on its microstructure, and is promising as an inorganic imaging powder.