Broadband down-conversion through the co-contribution of simultaneous energy transfer from Eu3+/2+ to Yb3+ and CTS absorption of Yb3+.

The europium (Eu) and ytterbium (Yb) co-doped SiO 2 –Al 2 O 3 –MF 2 (M = Ca, Sr) oxyfluoride glasses were prepared by the melting-quenching method, in which the partial reduction of Eu 3+ ions during high temperature fabrication in air atmosphere was explained by optical basicity model. In this system, the near-infrared emission of Yb 3+ at 974 nm can be observed upon the excitation of both Eu 3+ and Eu 2+ , as well as charge transfer state absorption of Yb 3+ . The steady and time-resolved luminescence spectra measurements were carried out to further prove the energy transfer from Eu 3+/2+ ions to Yb 3+ . Based on the measured luminescence decay of Eu 3+ and Eu 2+ , the energy transfer efficiency and the quantum efficiency are much higher in the glass containing SrF 2 due to the efficient energy transfer from both Eu 3+ and Eu 2+ to Yb 3+ . [ABSTRACT FROM AUTHOR]