摘要： Lead halide perovskites nanocrystals (NCs) have attracted intense attentions because of their excellent optoelectronic properties. The ionic nature of halide perovskites makes them highly vulnerable to water. Encapsulation of perovskite NCs with inorganic or organic materials have been reported to enhance the stability, however they often suffer from large aggregation size, low water-solubility and difficulty for further surface functionalization. Here, we report a facile aqueous process to synthesize water-soluble CsPbBr3/Cs4PbBr6 NCs with the assistance of fluorocarbon agent, which features a novel mechanism of the perovskite crystallization at oil/water interface and direct perovskite NCs/fluorocarbon agent self-assembly in aqueous environment. The products exhibit a high absolute photoluminescence quantum yield (PLQY) of ~80% in water with the photoluminescence lasting for weeks. Through successive ionic layer adsorption and reaction (SILAR), BaSO4 was further applied to encapsulate the NCs, and greatly enhanced their stability in phosphate buffered saline solutions. The high stability in water and saline solution, high PLQY and tunable emission wavelength, together with the successful demonstration of brain tissue labelling and photoluminescence under X-ray excitation, make our perovskite NCs a promising choice for X-ray fluorescent bio-labels.