Bright and tunable emissive monodisperse CsPbI3@Cs4PbI6 nanocomposites via a precise and controllable dissolution—recrystallization method

Nowadays, due to uncontrolled synthesis and lack of more direct and systematic evidences, the photoluminescence origin of "zero-dimensional" Cs4PbI6 remains great controversy and the luminescence cannot be controlled. Here we propose a controllable dissolution-recrystallization method to synthesize "emissive" and "non-emissive" Cs4PbI6 nanocrystals (NCs) respectively. Through comparing "emissive" and "non-emissive" Cs4PbI6 NCs, it is clearly proved that the visible emission in "emissive" Cs4PbI6 NCs comes from embedded CsPbI3 quantum dots (QDs). It is found for CsPbI3@Cs4PbI6 nanocomposites, methyl acetate (MeAC) and cyclohexane play an important role in dissolution and recrystallization respectively to obtain Cs4PbI6 matrix and CsPbI3 cores. Benefiting from this two-step method, the as-synthesized CsPbI3@Cs4PbI6 nanocomposites with CsPbI3 QDs uniformly distributed in Cs4PbI6 matrix are bright with photoluminescence quantum yield (PLQY) up to 71.4% and exhibit improved stability than CsPbI3 NCs. Moreover, utilizing its formation mechanism, the size of embedded CsPbI3 QDs can be controlled by reasonable designing the "dissolution" process, so that the luminescence of this CsPbI3@Cs4PbI6 nanocomposites can be adjusted in a wide range from green to red (554–630 nm). Our finding not only provides a novel method for synthesizing tunable "emissive" Cs4PbI6 NCs, but also makes clear the photoluminescence origin of "emissive" Cs4PbI6.