Energy transfer from Yb to X (X = Tm, Er) in lead borate glasses

Energy transfer processes in lead borate glasses doubly doped with Yb-Tm and Yb-Er have been investigated at room temperature under excitation of Yb at 975 nm. The non-resonant energy transfer from 2F5/2 state of Yb to 3H5 state of Tm results in up-converted emission at 850 nm due to the 3H4-3H6 transition of thulium ions. The nearly resonant transfer from 2F5/2 state of Yb to 4I11/2 state of Er results in green up-conversion and near-infrared emission, which correspond to the 4S3/2-4I15/2 and 4I13/2-4I15/2 transitions of erbium ions, respectively. High Yb concentration in both co-doped samples is required for optimal energy transfer efficiency (h > 90%). Results with the singly Yb-doped samples are also presented to clarify the energy transfer process.