Intragap State Engineering for Tunable Single-Photon Upconversion Photoluminescence of Lead Halide Perovskite

High-efficiency single-photon upconversion photoluminescence (SPUC-PL) has been reported in diverse lead halide perovskite materials, bringing them unique applications in optics and optoelectronics. However, because of the lack of reliable protocols for tuning the individual SPUC-PL indexes, their feasibility and flexibility in practice are still highly limited. In this work, the mechanism of the perovskite-based SPUC-PL is systematically studied. We report that the energetic distribution of the intragap electronic states determines the SPUC-PL quantum yield and the anti-Stokes shift, two critical spectroscopic indexes, in a trade-off manner. On the basis of this finding, we propose a viable method of tuning SPUC-PL parameters in terms of the intragap state engineering strategy. Specifically, by controlling the thermal annealing temperature, the SPUC-PL quantum yield and the anti-Stokes shift can be effectively adjusted as desired. This work provides new insights into the deployment of lead halide perovskites as the controllable SPUC-PL media.