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.

Near-infrared (NIR) persistent-luminescence nanoparticles have emerged as a new class of background-free contrast agents that are promising for in vivo imaging. The next key roadblock is to establish a robust and controllable method for synthesizing monodisperse nanoparticles with high luminescence brightness and long persistent duration. Herein, we report a synthesis strategy involving the coating/etching of the SiO₂ shell to obtain a new class of small NIR highly persistent luminescent ZnGa₂O₄: Cr³⁺, Sn⁴⁺ (ZGOCS) nanoparticles. The optimized ZGOCS nanoparticles have an excellent size distribution of ~15 nm without any agglomeration and an NIR persistent luminescence that is enhanced by a factor of 13.5, owing to the key role of the SiO₂ shell in preventing nanoparticle agglomeration after annealing. The ZGOCS nanoparticles have a signal-to-noise ratio ~3 times higher than that of previously reported ZnGa₂O₄: Cr³⁺ (ZGC-1) nanoparticles as an NIR persistent-luminescence probe for in vivo bioimaging. Moreover, the persistent-luminescence signal from the ZGOCS nanoparticles can be repeatedly re-charged in situ with external excitation by a white lightemitting diode; thus, the nanoparticles are suitable for long-term in vivo imaging applications. Our study suggests an improved strategy for fabricating novel high-performance optical nanoparticles with good biocompatibility.