Synthesis of CsPbBr2Cl Nanocrystals. CsPbBr2Cl Nanocrystals were made by a Hot-Injection synthesis using a modified literature method . To synthesize ~ 12 nm CsPbBr2Cl nanocrystals, 49 mg (0.15 mmol) Cs2CO3, 67 mg (0.3 mmol) PbO and 1.5 mL oleic acid (OA) were degassed in 15 mL ODE in a 50 mL three-neck flask under reduced pressure at 120 °C for 1 h. Then the temperature increased to 260 °C under nitrogen atmosphere, 1 mL OLA-HBr and 0.5 mL OLA-HCl precursor were quickly injected and after 5 min the reaction mixture was cooled to room temperature (using an ice-bath below 180 °C).