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

Infrared-to-visible upconversion fluorescence of Er^3＋/Yb^3＋ 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 Yb^3＋-Er^3＋ 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 → ^4I15/2, ^4S3/2→ ^4I15/2, and ^4 F9/2 →^4I15/2, 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 Er^3＋/yb^3＋ co-doped LSPB glasses may be a potentially useful material for developing upconversion optical devices.