Phase Regulation and Surface Passivation of Stable alpha-CsPbI3 Nanocrystals with Dual-Mode Luminescence via Synergistic Effects of Ligands

Cubic-phase CsPbI3 perovskite nanocrystals (CsPbI3 NCs) are widely used as a promising luminescent material in optical devices such as light-emitting diodes and lasers due to their high photoluminescence quantum efficiency and excellent color purities. However, the CsPbI3 lattice is more likely to face the problem of phase transformation due to the poor thermodynamic stability, which would lead to the decrease of its photoluminescence quantum efficiency. In this work, alpha-CsPbI3 NCs were synthesized by the room-temperature dual-ligand-assisted re-precipitation method under the synergistic effect of n-octanoic acid (OTAC), oleylamine (OLA), and (3-aminopropyl)triethoxysilane (APTES). The anionic OTAC and cationic OLA ligands interacted with the Pb2+ and I-, respectively, on the surface of the alpha-CsPbI3 NCs to passivate the defects on the surface. By the adjustment to the volume ratio of the OTAC to OLA, the synergistic effects of the dual ligands inhibited the distortion of the octahedral [PbI6](4-) and maintained the cubic perovskite structure of the alpha-CsPbI3 NCs. The hydrolysis of APTES into the silica layer would provide efficient environmental protection and maintain the cubic phase of alpha-CsPbI3 at room temperature. The alpha-CsPbI3 NCs not only produce strong red emission upon the UV excitation but also exhibit strong up-conversion luminescent properties upon the near-infrared excitation at a low excitation power laser of 1064 nm, showing dual-mode luminescent characteristics as a promising material for potential applications in optical devices.