Tailoring the Highly Efficient Upconversion Luminescence of All‐Inorganic Er3+‐Based Halide Double Perovskites by Introducing Various Energy Trapping Centers

Abstract Rare‐earth ions doped halide double perovskites are considered as promising luminescent materials. However, the contradiction of fluorescence quenching at high concentrations and the lack of sufficient upconversion photoluminescence (UCPL) emitters remain a significant challenge. Here, a lead‐free Er 3+ ‐based halide double perovskite Cs 2 NaErCl 6 is reported, which exhibits bright orange and green UCPL emission under 980 and 808 nm laser excitation, respectively. Subsequently, the UCPL emission intensity is greatly enhanced and the emission color is tunable by introducing different energy trapping centers. Importantly, under 980 nm laser excitation, the facilely prepared Yb 3+ ‐ and Tm 3+ ‐doped Cs 2 NaErCl 6 perovskites exhibit remarkably efficient multicolor upconverting emission, which is comparable to or even outperformes the commercial UCPL phosphor prepared by the high‐temperature solid‐state method. Meanwhile, the UCPL mechanisms involved in the energy transfer upconversion and excited‐state absorption are also explored, which can promote a better understanding of the UCPL processes. Moreover, these efficient multimode luminescence features show great potential in anticounterfeiting applications.