Upconversion emission of a novel glass ceramic containing Er3+, Yb3+ : Sr1-xYxF2, 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 degrees 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 degrees C. The measurements were based on analyzing the lifetimes of the S-4(3/2) and I-4(11/2) levels of erbium and the F-2(5/2) level of ytterbium. Ytterbium and erbium ions started to incorporate into the crystalline phase when the heat treatment temperature was more than 650 degrees C and 600 degrees C, respectively. The sample that was heat treated at 750 degrees 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 S-4(3/2) (Er3+) and F-2(5/2) (Yb3+ levels were increased to 500 mu s 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. (C) 2015 Elsevier B.V. All rights reserved.