Ionic Liquid-Assisted Preparation of Pure Blue Emissive CsPbBr₃ Nanoplates with Enhanced Fluorescence and Stability

Pure blue-emitting CsPbBr₃ nanocrystals suffer from poor stability and low photoluminescence quantum yields (PLQY), severely limiting their application in optoelectronic devices. Herein, we synthesized CsPbBr₃ nanoplates (NPLs) with pure blue emission at 463.3 nm via a room-temperature supersaturation recrystallization approach by tuning the Pb/Cs molar ratio. To enhance the emission performance of CsPbBr₃ NPLs, the ionic liquid (IL) 1-amino propyl-3-methyl imidazolium tetrafluoroborate (APMimBF₄) was introduced, in which the [BF₄]^- anion of the IL effectively passivates Br vacancy defects on the NPL surface. Additionally, the stability of the NPLs was enhanced by the [APMim]BF₄ due to the strong binding affinity between [APMim]⁺ and undercoordinated surface Pb²⁺ ions. This dual passivation significantly suppresses nonradiative recombination pathways, resulting in an increase of PLQY from 39.14 to 85.67%. The as-prepared CsPbBr₃ NPLs were encapsulated within a polystyrene-block-polyisoprene-block-polystyrene matrix, forming composite films for the fabrication blue LEDs. Owing to the effective surface passivation, the resulting LEDs exhibit exceptional operational stability-evidenced by negligible CIE color coordinates shifts during operation. This study presents a promising IL-based surface engineering strategy for simultaneously enhancing the luminescence efficiency and environmental stability of pure blue emissive CsPbBr₃ NPLs, promoting their practical application in optoelectronic devices.