Solution-State Cooperative Luminescence Upconversion in Molecular Ytterbium Dimers

Abstract

Two homometallic ytterbium dimers are prepared and their solution-state photoluminescence and upconversion properties are investigated. Both complexes exhibit two-photon cooperative luminescence upconversion in the visible region (λem ≈ 510 nm) upon excitation into the near-infrared Yb 2F5/2 ← 2F7/2 absorption band at 980 nm. This miniaturization of the cooperative luminescence phenomenon down to just two Yb ions unequivocally proves the mechanistic origins of this process. Time-resolved measurements and excited-state modeling indicate the presence of a slow recombination of two singly excited ions Yb*Yb* into a virtual excited state, which ultimately gives rise to the observed emission at ≈510 nm.