A Dual-Passivation Strategy to Enhance Exciton Luminescence and Bimodal Anticounterfeiting in Red Perovskite Quantum Dots

Perovskite quantum dots (PQDs) face significant performance limitations due to surface defects, which are not sufficiently addressed by conventional single-passivation methods. We introduce a dual-passivation strategy that synergistically combines bifunctional ligand 3-(N,N-dimethyloctadecylammonium)-propanesulfonate (SB3-18) treatment with silica coating to simultaneously passivate undercoordinated Pb2+ ions and bromine vacancies in red-emitting CsPb(Br/I)3 PQDs. This approach nearly triples the photoluminescence quantum yield (PLQY, from 23% to 58%). Systematic structural, morphlogical, binding energy, Fermi level and optical analyses confirm effective defect suppression and enhanced exciton luminescence. The dual-passivated sample QDs:SB3-18@SiO2 also exhibit excellent environmental stability, retaining 85% of their initial emission after 30 min in air and exhibiting improved UV resistance. By combining the PQDs with a CGSO:Tb3+ mechanoluminescent phosphor, a composite film is fabricated with bimodal optical response—color-selective photoluminescence under UV excitation and stress-activated green emission upon scratching. This work presents a robust route to high-performance PQDs and demonstrates their potential for advanced anticounterfeiting and smart optical applications.