PMC

Evolution of the optical absorption (solid lines) and PL (dashed lines) spectra of CsPbBr₃ NCs with increasing quantities of PbCl₂ or PbI₂, added as exchanging halide sources.

In-situ PL measurements during a CsPbBr₃ to CsPbI₃ NC conversion at 40 °C with [Br]_parent/[I]_incoming = 1:3, (a) plotted at specific times during conversion and (b) throughout the complete process (with three spectra acquired per second).

Inter-NC anion-exchange reactions in CsPbX₃ NC systems. (a) An overview of the PL spectra of samples obtained by mixing CsPbBr₃ NCs with either CsPbCl₃ or CsPbI₃ NCs in various ratios. (b) Time-dependent PL spectra showing an intermediate stage formed during inter-NC anion-exchange between CsPbBr₃ and CsPbI₃ in which two distinct NC species coexist with altered compositions.

Transmission electron microscopy (TEM) images of ∼10 nm CsPbX₃ NCs after treatment with various quantities of (a) chloride and (b) iodide anions. The insets show the evolution of emission colors (under a UV lamp, λ = 365 nm) upon forming mixed-halide CsPb(Br/Cl)₃ and CsPb(Br/I)₃ to fully exchanged CsPbCl₃ and CsPbI₃ NCs.

(a) Schematic of the anion-exchange within the cubic perovskite crystal structure of CsPbX₃ along with a list of suitable reagents for each reaction when performed in organic media. A three-dimensional network is formed by corner-sharing PbX₆ octahedra with Cs⁺ (purple spheres) occupying the interstitial voids. Ionic radii: Cs⁺, 1.88 Å; Pb²⁺, 1.16 Å; Cl^–, 1.81 Å; Br^–, 1.96 Å; and I^–, 2.2 Å.⁻ (b) Powder X-ray diffraction (XRD) patterns of the parent CsPbBr₃ NCs and anion-exchanged samples (using PbCl₂ and PbI₂ as halide sources), showing the retention of phase-pure cubic perovskite structure and an average (Scherrer) crystallite size of 8–10 nm. The shift of the XRD reflections is linearly dependent on the composition (Vegard’s law), indicating the formation of uniform solid solutions. Equivalent behaviors were also observed for CsPbCl₃ + Br^– and CsPbI₃ + Br^– systems. Formation of solid solutions has been also confirmed by energy dispersive X-ray spectroscopy (EDX) and Rutherford backscattering spectrometry (RBS).