Facet\n{100} Fosters\nResonance Energy Transfer in Ni/Co-Doped\nCsPbBr<sub>3</sub> Nanocrystals

The design of an effective light\nharvester with metal-doped\nperovskite\nnanocrystals (M:PNCs) aims to achieve directional energy flow. The\npotential of crystal facets needs to be assessed for dictating the\nenergy transfer dynamics of M:PNCs. Herein, we have engineered facets\nof amine-capped CsPbBr<sub>3</sub> perovskite nanocrystals by doping\nwith a trace amount of Ni and Co ions. Ni-doped CsPbBr<sub>3</sub> (Ni:PNC) showcases structural heterogeneity with regular cubic \nshape, whereas bimetallic-doped CsPbBr<sub>3</sub> (Ni:Co:PNC) evolves\nto an elongated dodecahedron structure. Structural analysis using\nRietveld refinement strongly corroborates the construction of a dodecahedron\nstructure for Ni:Co:PNC through systematic displacement of Cs ions.\nEnergy transfer from doped nanocrystals to rhodamine B (RhB) occurs\nthrough a dipole–dipole interaction, known as Förster\nresonance energy transfer (FRET). The emergence of the isoemissive\npoint and rise time of RhB conclusively establish the resonance energy\ntransfer mechanism. Energy transfer in thin films occurs at a much\nfaster rate than in the toluene medium. {100} facet-dominated Ni:PNC\nregisters a FRET efficiency of 94%, whereas {111} and {002} facet-dominated\nNi:Co:PNC is restricted at 21% FRET efficiency. The distance between\nthe donor and acceptor, <i>R</i><sub>DA</sub>, dictates\nthe dynamics of energy transfer, rather than spectral overlap and\nthe photoluminescence quantum yield of these doped nanocrystals. The\nsurface composition of facets, typically Cs ions, perhaps plays a\ndecisive role in regulating the binding constant of the donor and\nacceptor. Our study demonstrates the importance of facets of nanocrystals\nin tuning the desired energy transfer processes for photocatalytic\napplications.