Intense frequency upconversion emission of Er3+/Yb3+-codoped natrium–barium–strontium–lead–bismuth glasses

Er3+/Yb3+-codoped natrium–barium–strontium–lead–bismuth glasses for developing potential upconversion lasers have been fabricated and characterized. Based on the results of energy transfer efficiency and upconversion fluorescence spectra, the optimal Yb3+–Er3+ concentration ratio is found to be 5:1. Intense green and red emissions centered at 525, 546, and 657 nm, corresponding to the transitions H 11 / 2 2 → I 15 / 2 4 , S 3 / 2 → I 15 / 2 4 and F 9 / 2 2 → I 15 / 2 4 , respectively, were observed at room temperature. The quadratic dependence of the 525, 546, and 657 nm emissions on excitation power indicates that a two-photon absorption process occurs under 975 nm excitation. The long-lived I 11 / 2 4 level is supposed to serve as the intermediate state responsible for the upconversion processes.