Repeatable fluorescence switcher of Eu3+-doped CeO2 nanorods by l(+)-ascorbic acid and hydrogen peroxide

Abstract

Inorganic phosphors of Eu³⁺-doped CeO₂ nanorods were synthesized by a hydrothermal method, followed by high temperature calcination. The phosphors with various doping concentrations of Eu³⁺ exhibited similar rod-like morphology. These phosphors with different Eu³⁺ contents can be effectively excited at 340 nm due to the charge transfer from O²⁻ to Ce⁴⁺, and display orange and red emissions of Eu³⁺. It was found that the fluorescence intensity of Eu³⁺-doped CeO₂ nanorods was exponentially decreased with increase in the concentrations of L(+)-ascorbic acid, resulting from the chemical reduction of Ce⁴⁺ into Ce³⁺ and the subsequent excitation cut-off of O²⁻ to Ce⁴⁺. The fluorescence intensity of reduced phosphors was restored to the original intensity reversibly by adding hydrogen peroxide, which oxidized Ce³⁺ into Ce⁴⁺. The evolution in fluorescence intensity was consistent with surface Ce³⁺ fractions of Eu³⁺-doped CeO₂ nanorods, which were 22.0% for as-synthesized phosphors, 34.6% for reduced phosphors and 23.2% for restorative phosphors oxidized by H₂O₂, respectively. The quantitative and repetitive fluorescence switching of Eu³⁺-doped CeO₂ nanorods by adding L(+)-ascorbic acid and hydrogen peroxide alternatively indicates their potential applications as fluorescence switching devices and chemical or biological sensors for detection and monitoring.