Stable deep blue photoluminescence from CsPbBr₃ quantum dots

Despite recent progress, it remains challenging to fabricate stable deep blue-emitting perovskites. Here, we propose a molecular etching strategy to obtain ultra-small CsPbBr₃ perovskite quantum dots (QDs) with robust deep-blue emission. The diphenylalanine (FF) with high polarity is used to break ionic bonds of CsPbBr₃ to strip off atomic layers from the QDs. Simultaneously, perfluoroglutaric acid (PFGA) ligands are employed to passivate the QDs surface, effectively overcoming the surface defects induced by ligand detachment. By adjusting the volume ratio of QD:FF solutions, the emission wavelength can be continuously tuned from 506 to 458 nm, yielding deep-blue emission with high color purity. Comprehensive analyses using transient absorption, time-resolved photoluminescence (PL), and temperature-dependent PL measurements indicate that the emission blueshift is primarily attributed to the enhanced quantum confinement effects resulting from the reduced size. Furthermore, a dual-level optical encryption strategy is proposed by leveraging the intrinsically higher photostability of ultra-small CsPbBr₃ than that of mixed halide CsPb(Cl/Br)₃ QDs. This work provides a viable pathway for fabricating high-efficiency, ultra-stable deep-blue emitting perovskite QDs, showing significant potential for advanced applications in high-resolution displays and optoelectronic encryption.