Quenching cooperative transitions by destroying Yb 3+ -clusters.

In our previous study, we have reported the cooperative luminescence of Yb3+-trimers and cooperatively sensitized Gd3+ luminescence by Yb3+- tetramers in a doped CaF2 host. In this study, we experimentally observed an unusual luminescent phenomenon of Gd3+ in CaF2: Yb3+/Gd3+. Upon excitation with a 980 nm laser, the upconversion luminescence of Gd3+ first increases and then decreases in the Gd3+ concentration range of 0-0.9 mol%; this is different from the monotonic increase of Gd3+ luminescence observed in the downconversion spectra via the direct excitation of Gd3+. This special luminescent behavior was indicated to be related to the energy transfer from the Yb3+- tetramers to Gd3+ and the destruction of Yb3+- clusters. Herein, we proposed a new luminescence quenching mechanism, Yb3+-cluster destructive quenching, which was verified by fluorescence dynamic analysis and an optically inactive rare-earth ion-doping experiment.