Two-photon excited red upconversion luminescence of thulium ions doped GeS2–In2S3–CsI glass

We report a novel phenomenon in GeS2–In2S3–CsI chalcohalide glass doped with Tm3+ ions. Under irradiation with an 808 nm laser diode, a bright red emission centered at 700 nm is observed for the first time in this glass. The log–log correlation between integrated emission intensity and pump power reveals that a two-photon absorption process is involved in the phenomenon, suggesting that the 3F3,2 → 3H6 transition of Tm3+ ions is responsible for the appearance of the red emission. The results indicate that the indium (In) based chalcohalide glass containing Tm3+ ions is expected to find applications in visible lasers, high density optical storage and three-dimensional color displays.