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The surface modification of perovskite nanocrystals (NCs) (i.e., their decoration with noble metals) holds great promise with respect to the tailoring of their properties but has remained a challenge because perovskite NCs are extremely sensitive to water and alcohols. In this study, Au or Pt@CsPbBr₃ NCs were successfully synthesized by photoreduction at the water/hexane interface. First, Cs₄PbBr₆ NCs were synthesized through the hot-injection method. Then, Cs₄PbBr₆ was transformed into CsPbBr₃ and subjected to noble metal modification, both at the interface. The synthesized CsPbBr₃ NCs exhibited a cubic perovskite phase and had an average size of approximately 13.5 nm. The deposited Au and Pt nanoparticles were crystalline, with a face-centered cubic lattice and average diameters of approximately 3.9 and 4.4 nm, respectively. The noble metal modification process had almost no effect on the steady-state photoluminescence (PL) emission wavelength but affected the charge-recombination kinetics of the CsPbBr₃ NCs. Time-resolved PL decay spectral analysis indicated that the fluorescence lifetimes of the Au and Pt@CsPbBr₃ NCs were shorter than those of the pure CsPbBr₃ NCs, probably owing to the quenching of the free charges because of electron transfer from the perovskite to the noble metal nanoparticles.