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 at achieving directional energy flow. The potential of crystal facets needs to be assessed for dictating 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 and rod shapes whereas bimetallic-doped CsPbBr3 (Ni:Co:PNC) evolves to an elongated dodecahedron structure. Structural analysis using Rietveld Refinement strongly corroborates the construction of dodecahedron structure for Ni:Co:PNC through systematic displacement of Cs ions. Energy transfer from doped nanocrystals to Rhodamine B (RhB) occurs through dipole-dipole interaction, known as Fluorescence Resonance Energy Transfer (FRET). The emergence of isoemissive point, and rise-time of RhB conclusively establish Resonance Energy Transfer mechanism. Energy transfer in thin films occurs at much faster rate than in toluene medium. {100} facet-dominated Ni:PNC registers a FRET efficiency of 94% whereas {111}, {002} facet-dominated Ni:Co:PNC restricts at 21% FRET efficiency. The distance between donor and acceptor, RDA dictates the dynamics of energy transfer, rather than spectral overlap, and photoluminescence quantum yield of these doped-nanocrystals. Surface composition of facets, typically Cs ions perhaps plays a decisive role in regulating the binding constant of donor and acceptor. Our study demonstrates the importance of facets of nanocrystals in tuning the desired energy transfer processes for photocatalytic applications.