Facet {100} Fosters Resonance Energy Transfer in Ni/Co-Doped CsPbBr3 Nanocrystals

The design of an effective light harvester with metal-doped perovskite nanocrystals (M:PNCs) aims to achieve directional energy flow. The potential of crystal facets needs to be assessed for dictating the energy transfer dynamics of M:PNCs. Herein, we have engineered facets of amine-capped CsPbBr3 perovskite nanocrystals by doping with a trace amount of Ni and Co ions. Ni-doped CsPbBr3 (Ni:PNC) showcases structural heterogeneity with regular cubic shape, whereas bimetallic-doped CsPbBr3 (Ni:Co:PNC) evolves to an elongated dodecahedron structure. Structural analysis using Rietveld refinement strongly corroborates the construction of a dodecahedron structure for Ni:Co:PNC through systematic displacement of Cs ions. Energy transfer from doped nanocrystals to rhodamine B (RhB) occurs through a dipole–dipole interaction, known as Förster resonance energy transfer (FRET). The emergence of the isoemissive point and rise time of RhB conclusively establish the resonance energy transfer mechanism. Energy transfer in thin films occurs at a much faster rate than in the toluene medium. {100} facet-dominated Ni:PNC registers a FRET efficiency of 94%, whereas {111} and {002} facet-dominated Ni:Co:PNC is restricted at 21% FRET efficiency. The distance between the donor and acceptor, RDA, dictates the dynamics of energy transfer, rather than spectral overlap and the photoluminescence quantum yield of these doped nanocrystals. The surface composition of facets, typically Cs ions, perhaps plays a decisive role in regulating the binding constant of the donor and acceptor. Our study demonstrates the importance of facets of nanocrystals in tuning the desired energy transfer processes for photocatalytic applications.