Water-induced fluorescence enhancement of lead-free cesium bismuth halide quantum dots by 130% for stable white light-emitting devices
Recently, the discovery and development of lead-free perovskites quantum dots (QDs) that are eco-friendly and stable has become an active research area in low-cost lighting and display fields. However, the low photoluminescence quantum yield (PLQY) caused by the residual surface states for such QDs seversely hinders their practical applications and commercialization. In this work, a strategy of water-induced nanocomposites was proposed to improve the PLQY of cesium bismuth halide (Cs3Bi2X9) QDs, and a substantial enhancement by ~130% (from 20.2% to 46.4%) was achieved by an optimized water treatment for Cs3Bi2Br9 QDs. Detailed analysis indicated that the Cs3Bi2Br9/BiOBr nanocomposites, in which the Cs3Bi2Br9 QDs core was encapsulated into BiOBr matrix, can effectively suppress the surface defects of QDs, resulting in longer PL lifetime and larger exciton binding energy compared with the pristine sample. Finally, the Cs3Bi2Br9/BiOBr nanocomposites were applied as the color-converting phosphors for down-conversion white light-emitting devices, which show a good operation stability in air ambient, significantly better than the reference device constructed with conventional lead-halide perovskites. We believe that the method used here provides an effective strategy to improve the fluorescence efficiency of lead-free perovskite QDs, which will create opportunities for lighting and display applications.