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Fig. 1  Schematic diagram of partial substitution of Pb²⁺ with Fe²⁺ in CsPbBrI₂ perovskite.

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Fig. 2  XRD patterns of undoped CsPbBrI₂ NCs, Br-2.4%, Ac-2.1%, F-1.7%. Enlarged XRD patterns show a systematic shift in peak position of (100) and (200) planes with Fe²⁺ doping.

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Fig. 3  Structure of CsPbBrI2 NCs. (a-d) TEM and HR-TEM images of undoped CsPbBrI₂ NCs, Br-2.4%, Ac-2.1%, F-1.7%. (e) Survey XPS spectra and (f-i) HR-XPS spectrum of Cs, Pb, Br and I for CsPbBrI₂ NCs.

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Fig. 4  Luminescence performance of CsPbBrI₂ NCs. (a) Steady state absorption (dotted line) and PL (solid line) spectra of CsPbBrI₂ NCs. Inset shows the photographs of PNCs in hexane under UV-light (365 nm) irradiation. (b) The PLQY values of CsPbBrI₂ NCs synthesized with different iron precursors. (c) Time-resolved photoluminescence decays for excitonic luminescence of the samples upon excitation by a 375-nm pulsed laser.

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Fig. 5  Cubic phase and PL stability tests of as-synthesized CsPbBrI₂ NCs in the forms of colloidal suspension (in hexane) and thin film. (a) PLQYs of CsPbBrI₂ NCs in hexane exposed in the environment for different days. Environment: 25 °C with 20 % relative humidity. (b) Photos of fresh and aged CsPbBrI₂ NCs suspension (in hexane, storage under ambient conditions) under UV-light (365 nm) irradiation. (c) The PLQY variation of CsPbBrI₂ NCs suspension (in hexane) exposed to UV-light (365 nm) irradiation for different days. The PL evolution of (d) undoped CsPbBrI₂ NCs, (e) Br-2.4%, (f) Ac-2.1%, (g) F-1.7% film under ultraviolet light. (h) Photos of CsPbBrI₂ NCs thin films exposed to UV-light (365 nm) irradiation for different days.