Intense frequency upconversion fluorescence of Er~(3+)/Yb~(3+) co-doped lithium-strontium-lead-bismuth glasses

Infrared-to-visible upconversion fluorescence of Er3+/Yb3+ co-doped lithium-strontium-lead-bismuth (LSPB) glasses for developing potential upconversion lasers has been studied under 975-nm excitation. Based on the results of energy transfer efficiency and upconversion 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 2H11/2→4 I15/2, 4S3/2→4 I15/2, and 4F9/2→4 I15/2, respectively, were observed. 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 high-populated 4I11/2 level is supposed to serve as the intermediate state responsible for the upconversion processes. The intense upconversion luminescence of Er3+ /Yb3+ co-doped LSPB glasses may be a potentially useful material for developing upconversion optical devices.