Room-temperature visible upconversion luminescence of Ni2+ sensitized by Yb3+ in transparent glass ceramics

Upconversion luminescence of transition metal Ni2+ ions is seldom at room temperature (RT) due to large non-radiative transition probability. Here, a green Ni2+ upconversion luminescence at RT is obtained by the near-infrared excitation of Yb3+ 2F7/2 → 2F5/2 at 980 nm in Ni2+/Yb3+ codoped transparent wide bandgap semiconductor γ-Ga2O3 glass ceramics, which can be assigned to the Ni2+ 1T2(1D) → 3A2(3F) transition. Lifetime measurement and upconversion power dependence data reveal energy transfer upconversion as the underlying upconversion mechanism for the Yb3+-Ni2+ systems incorporated into the γ-Ga2O3 nanocrystals. It is suggested that the low thermal quenching effect of the wide bandgap semiconductor γ-Ga2O3 and resonant sensitizing of the Yb3+ 2F5/2 state to the Ni2+ upconversion 3T2(3F) intermedia state are responsible for the achievement of room-temperature upconversion luminescence of Ni2+. The results demonstrate that wide bandgap semiconductor nanocrystal (γ-Ga2O3, TiO2, SnO2, et al.) glass ceramics may be a good candidate for hosting Ni2+ room-temperature upconversion luminescence.