High PLQY and Ultra‐Stable Cs 2 ZnCl 4 /SiO 2 Nano‐Composite Particles From Lead‐Free Perovskite Colloidal Quantum Dots

All‐inorganic lead‐free Cs 2 ZnCl 4 perovskite quantum dots (QDs) attract significant attention due to their non‐toxicity and unique optoelectronic properties. However, the yield of Cs 2 ZnCl 4 colloidal QDs synthesized via ligand‐assisted reprecipitation (LARP) remains extremely low, and their stability is poor, limiting their applications. Here, we report a post‐processing strategy that employs mesoporous nano‐SiO 2 to anchor Cs 2 ZnCl 4 QDs within its pores, creating spatial confinement that prevents Cs 2 ZnCl 4 QDs aggregation and quenching while passivating surface defects and reducing non‐radiative recombination pathways. This strategy enables the powderization of Cs 2 ZnCl 4 colloidal QDs, and the Cs 2 ZnCl 4 /SiO 2 nano‐composite particles (NCP) exhibit bright blue photoluminescence (CIE 0.15, 0.12). Compared to the Cs 2 ZnCl 4 colloidal QDs, the Cs 2 ZnCl 4 /SiO 2 NCP demonstrates a 10 times increase in PL intensity, with a high PLQY (74.28%) and an ultrafast photoluminescence lifetime (2.4 ns). Moreover, due to nano‐SiO 2 protection, the Cs 2 ZnCl 4 /SiO 2 NCP exhibits excellent ambient conditions (>6 months, 86.6%) and harsh conditions (temperature, humidity, light, etc.) stability, which is superior to that of other reported halide perovskite QDs. This strategy offers a viable approach to address the challenges of low yield, low photoluminescence efficiency, and poor stability in colloidal perovskite QDs, thereby creating opportunities for their commercial application.