Synthesis of Perovskite Nanoplates: 1 mL of the Cs/Pb precursor was dissolved in 4.5 mL of ODE and 0.5 mL of oleylamine. The mixture is heated to 110 °C under reduced pressure for at least 1 h. After this time, the mixture is kept in the temperature of the reaction (in the case of this work, 110 and 170 °C), and 2 mL of the SnX4 precursor solution is swiftly injected into the Cs/Pb solution. The SnX4 precursor is pre-heated to 100 °C under reduced pressure before the injection. In the case of CsPbI3 PNPls, the reaction is quenched immediately after the injection with an ice/water bath. In the case of CsPbBr3 PNPls, the reaction is quenched after 30 s after the injection with ice/water bath. To precipitate the product from the synthesis of CsPbBr3 at 110 °C by centrifugation (see next section), an addition 0.5 mL of oleic acid was added to the Cs/Pb precursor solution. With the original synthesis, very little or almost no precipitate is formed upon centrifugation.