Upconversion emission of a novel glass ceramic containing Er3+, Yb3+:Sr1−xYxF2+x nano-crystals

Transparent oxyfluoride glass ceramics with a novel composition of Er3+, Yb3+:Sr1−xYxF2+x nano-crystals were processed. When excited under infrared light, an intense green upconverted luminescence was observed for the glass ceramic obtained from the precursor glass after a heat treatment of 4 h at 750 °C. X-ray diffraction and transmission electron microscopy analysis confirmed the precipitation of Sr1−xYxF2+x nano-crystals of sizes in the range of 9-45 nm in the heat treated samples. The position of Er3+, Yb3+ ions in the sample (either amorphous or crystalline phases) was studied at four different heat treatment temperatures of 600, 650, 700 and 750 °C. The measurements were based on analyzing the lifetimes of the 4S3/2 and 4I11/2 levels of erbium and the 2F5/2 level of ytterbium. Ytterbium and erbium ions started to incorporate into the crystalline phase when the heat treatment temperature was more than 650 °C and 600 °C, respectively. The sample that was heat treated at 750 °C for four hours showed the highest green upconversion intensity among the other heat treated samples. In this sample, majority of Er3+, Yb3+ ions were in the crystalline phase as the lifetime of 4S3/2 (Er3+) and 2F 5/2 (Yb3+) levels were increased to 500 μs and 2 ms, respectively, which are longer than their values in the precursor glass. High ion solubility of Er3+ and Yb3+ in the novel Sr1−xYxF2+x nano-crystals and their local environments in the nano-structure are believed to be the reasons for this high intense green upconversion.