All-Inorganic Zero-Dimensional Sn-Doped Rb4CdCl6 with Near-Unity Quantum Efficiency

Zero-dimensional (0D) metal halide perovskites (MHPs) have attracted much attention due to their unique crystal and electronic structure. Drastically different from three-dimensional (3D) CsPbCl3 analogues, 0D perovskites exhibit broadband emission spectra of self-trapped excitons (STEs) with a large Stokes shift and high exciton binding energy. However, their luminescent efficiencies are much lower than those of the 3D ones. Herein, for the first time, we successfully synthesized the Sn2+-doped 0D Rb4CdCl6 with an emission at 485 nm by a simple hydrothermal method. Importantly, the host with a doping of 0.239 Sn shows a near-unity quantum efficiency (PLQY -98.04%) under UV light excitation, which is the highest among Cd-based all-inorganic MHPs. The results from temperature-dependent PL spectra suggested that the emission might originate from STEs, where this broad emission is attributed to the 3P1 to 1S0 radiation transition of octahedral [SnCl6]4- units in the host matrix. As a result, the as-prepared doped crystals exhibit large Stokes shifts and high quantum efficiency. Our work successfully elucidates that the Sn2+ dopant plays an integral role in improving PLQY of 0D MHPs. This kind of Sn2+-doped promising luminescent materials may have significant applications in optoelectronic devices.