Water-Stable CsPbBr₃/Cs₄PbBr₆ Nanocrystals with a Mixed Fluoropolymer Shell for Optical Temperature Sensing

Hyflon AD 60 and dodecafluoroheptylpropyl-trihydroxysilane are employed as ligands to synthesize water-stable core–shell CsPbBr3/Cs4PbBr6 nanocrystals in aqueous dispersion, with a high photoluminescence quantum yield of 73% and a long luminescence lifetime of 207 ns. The obtained CsPbBr3/Cs4PbBr6 NCs passivated by fluorinated ligands are well dispersed in water with a mean diameter of 21.9 nm. The whole synthesis can be performed at room temperature on air; fluorinated chains of the Hyflon ligand strongly bond on the surface of CsPbBr3/Cs4PbBr6 nanocrystals and further link amphiphilic fluorinated silanol molecules through hydrophobic interactions. CsPbBr3/Cs4PbBr6 nanocrystals are stable in the aqueous phase for at least 1 month, maintaining strong photoluminescence (68% of initial intensity after 31 days) because of surface passivation. They are used as a luminescent temperature probe in water with a sensitivity of its intensity equal to 1.01% K–1 and good thermal stability for 10 heating–cooling cycles between 278 and 328 K.