Quenching Cooperative Transitions by destroying Yb3+-clusters
Our previous work reported cooperative luminescence of Yb3+-trimers and cooperatively sensitized Gd3+ luminescence by Yb3+-tetramers in doped CaF2 host. In this work, 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+ increases first and then decreases in the Gd3+ concentration range of 0-0.9 mol%, which is different from the monotonic increase of Gd3+ luminescence observed in the downconversion spectra by direct excitation of Gd3+. This special luminescent behavior is indicated to relate to energy transfer from Yb3+-tetramers to Gd3+ and destruction of Yb3+-clusters. Here, we proposed a new luminescence quenching mechanism, Yb3+-cluster destructive quenching, which is verified by fluorescence dynamic analysis and optically inactive rare earth ion doping experiment.