Efficient frequency upconversion emission in Er3+-doped novel strontium lead bismuth glass

Er3+-doped strontium lead bismuth glass for developing upconversion lasers has been fabricated and characterized. The Judd-Ofelt intensity parameters Ωt (t = 2, 4, 6), calculated based on the experimental absorption spectrum and Judd-Ofelt theory, were found to be Ω2 = 2.95 × 10−20, Ω4 = 0.91 × 10−20, and Ω6 = 0.36 × 10−20 cm2. Under 975 nm excitation, intense green and red emissions centered at 525, 546, and 657 nm, corresponding to the transitions 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, and 4F9/2 → 4I15/2, respectively, were observed. The upconversion mechanisms are discussed based on the energy matching and quadratic dependence on excitation power, and the dominant mechanisms are excited state absorption and energy transfer upconversion for the green and red emissions. The long-lived 4I11/2 level is supposed to serve as the intermediate state responsible for the upconversion processes.