Quenching cooperative transitions by destroying Yb3+-clusters

Abstract

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.