Redox-induced dual optical switching of CaTiO₃:Pr³⁺ phosphor nanoparticles synthesized by sol–gel method

Red-emitting CaTiO₃:Pr³⁺ phosphor nanoparticles were synthesized by a sol–gel method with a final heat treatment at a low temperature of 650 °C. For comparison, the CaTiO₃:Pr³⁺ phosphor was also synthesized by a conventional solid-state reaction method conducted at 1250 °C. The two kinds of resultant CaTiO₃:Pr³⁺ samples were revealed to differ largely in their microstructure and optical properties. Diffuse reflectance and photoluminescence measurements suggested that the sample from the solid-state reaction possessed a larger number of defects, which would deteriorate the optical properties, due to heating at high temperature. On the other hand, the sol–gel-derived sample exhibited much better optical properties and thus it was used for evaluating optical-switching phenomena upon redox treatments. In photoluminescence, three excitation bands were observed at 265, 335, and 375 nm for the red emission of the CaTiO₃:Pr³⁺ sample, and one of them (375 nm) was more effective for inducing luminescence quenching by a reduction treatment at room temperature. A body color of the CaTiO₃:Pr³⁺ sample was also changed from white to light yellow by the reduction due to the enhanced visible-light absorption. Such the dual luminescence/absorption switching was shown to be reversible with a subsequent oxidation and repeatable with a consecutive redox treatment. [Figure not available: see fulltext.]