Optical properties and valence change of samarium ions in a sol–gel Al2O3–B2O3–SiO2 glass by femtosecond laser irradiation

10Al2O3–5B2O3–85SiO2–xSm2O3 glasses were prepared by the sol–gel method. The emission spectra of the glasses indicate that the quench concentration of the Sm3+ ions is about 0.2 mol%. The emission spectra of the glasses after high-temperature treatment with H2 gas exhibit the coexistence of the Sm3+ and Sm2+ ions. We observed the strong emission line of the Sm2+ ions and the emission band of the non-bridging oxygen hole center when the glasses were exposed to a femtosecond laser. It indicates that some Sm3+ ions were reduced to Sm2+ ions by femtosecond laser pulses and non-bridging oxygen hole centers were formed. The 5D0–7F0 emission line of the Sm2+ ions by femtosecond laser irradiation shows a red shift, compared with the emission of the Sm2+ ions by reduction with H2 gas. The strong absorption band and weak, sharp absorption lines in the range from the UV to IR come from charge transfer and the transition from the 6H5/2 state to the various excited states of the Sm3+ ions. The reduction mechanism of Sm3+ ions is discussed.