Spectral properties and anti-Stokes luminescence of TeO 2 –BaF 2 :Ho 3+ , Ho 3+ /Yb 3+ ceramics and glass excited by 1.9-μm radiation of a Tm:LiYF 4 laser

We demonstrate the up-conversion of Tm:LiYF4 infrared (IR) laser radiation with 1908-nm wavelength into visible light with a spectral maximum at 650 nm by ceramics with a composition of (100 − x)TeO2−xBaF2 − 1 wt % HoF3−yYbF3, where x = 20, 30, or 40 mol % and y = 0 or 0.5 wt %. The samples of 60TeO2−40BaF2 − 1 wt % HoF3 − 0.5 wt % YbF3 exhibited anti-Stokes luminescence at a threshold radiation power density of 1.0−1.5 W cm−2.