Cesium halide lead (CsPbX 3 ) perovskite nanocrystals (NCs) have been extensively studied in recent years for their unique capability of postsynthesis anion exchange, providing facile tunability of band gaps and optical properties. In this work, we demonstrate for the first time a simple approach to the tunable anion exchange of CsPbX 3 perovskite NCs via radiation chemistry of inert halohydrocarbons. The anion exchange extents are monitored by shifting of fluorescence emission peaks and ultraviolet−visible absorbance edges and are precisely controlled by tuning the absorbed doses and the adjustable addition of halohydrocarbons. At the same absorbed doses, the anion exchange extents by halohydrocarbons are dependent on the linear attenuation coefficients of halohydrocarbons. Radiation-induced anion exchange can passivate defects in CsPbX 3 NCs, resulting in the fluorescence enhancement. The morphology of perovskite NCs almost remains intact after radiation-induced anion exchange.

It is still challenging to achieve both good stability and high PLQYs for perovskite NCs because of their ionic nature and structural defects. In this work, tungstosilicic acid (TSA) is used for the surface passivation of cesium lead halide perovskite NCs. Near-unity PLQY is achieved for CsPbBr3 NCs after surface passivation with a suitable amount of TSA. XRD in conjunction with XPS analysis shows that TSA binds hydrophobic chains of OAm onto the surface of CsPbBr3 NCs. XPS results also demonstrate that TSA passivation can change the charge distribution of the cations on the surface layers, which can enhance the interaction with surface traps. PL decay analysis reveals that trap states arising from the surface defects are significantly decreased after TSA passivation. TSA-passivated CsPbBr3 NCs demonstrate long-term ambient stability and good resistances to polar solvents and maintain about 80% of their initial PL intensity after storage under ambient conditions for 50 days. It is further found that TSA passivation is able to improve the PLQYs of a broad spectrum of CsPbX3 (X = Cl, Br, I) NCs without hindering the tunability of the band gaps and PL colors of CsPbX3 NCs via anion exchange.

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The evidence on deciphering nucleation and growth of cesium lead halide perovskite crystals, and establishing the phase diagram of cesium lead halide perovskites of different dimensions is still lacking. In this work, a facile method for the synthesis of cesium lead bromide crystals of different molecular level dimensions at room temperature is presented by varying the OA/OAm ratios without changing the proportions of Cs and Pb precursors. Bromide ions are gradually released in the systems through the gamma-ray radiation chemistry of bromobenzene. As the volume ratios of OA/OAm increase, different products such as CsBr, Cs 4 PbBr 6 (0D), white 𝜹-CsPbBr 3 (1D), 𝜸-CsPbBr 3 (3D) associated with PbBr 2 sheets, and 𝜸-CsPbBr 3 are obtained in order. 1D 𝜹-CsPbBr 3 can be transformed into 2D CsPb 2 Br 5 through CsBr stripping in water. The phase diagram established in this work is helpful for understanding the nucleation and growth mechanism of Cs-Pb-Br perovskite crystals of different dimensions. The nucleation of Cs-Pb-Br perovskite crystals is driven by the supersaturation of either CsBr or PbBr 2 caused by varying OA/OAm ratios, i.e., 0D Cs 4 PbBr 6 at the supersaturation of CsBr, while 3D 𝜸-CsPbBr 3 at the supersaturation of PbBr 2 . 1D perovskite is the intermediate state between 0D and 3D perovskites.