Femtosecond laser-induced reduction in Eu-doped sodium borate glasses

In this work, we report permanent reduction of Eu3+ to Eu2+ in sodium borate glasses by irradiation of near-infrared femtosecond laser. Glass composition of sodium borate was 85B2O3–15Na2O. The glasses were doped with 0.05, 0.1, and 0.5 mol% Eu2O3. Absorption and fluorescence dynamics were studied to investigate valence state change of europium ions and the energy transfer between Eu2+ and Eu3+ ions. As the femtosecond laser intensity or exposure time increases, the emission band at 400 nm becomes stronger. However, the photoreduction efficiency decreases as the dopant concentration increases. We discuss the photoreduction mechanism under multiphoton absorption.