Enhanced Dual-Emissive Circularly Polarized Luminescence of Mn2+-Doped 2D Lead Halide Perovskite Nanosheets Via l -Cysteine Modification

Mn2+-doped two-dimensional (2D) (PEA)2PbBr4 (PEA = phenethylammonium) nanosheets were synthesized and modified with chiral l-cysteine by room-temperature antisolvent recrystallization. Under 365 nm excitation, the optimized material exhibits dual-color photoluminescence (PL), comprising host excitonic emission at 410 nm and orange Mn2+ emission at 610 nm from the 4T1→6A1 transition. l-Cysteine increases the PL quantum yield from 33% to 71% and prolongs the average lifetimes of the excitonic and Mn2+ emissions from 1.9 to 3.0 ns and from 0.16 to 0.68 ms, respectively. Variable-temperature spectroscopy yields a low thermal activation barrier of 11.2 meV for host-to-Mn2+ energy transfer. Circular dichroism and dual-band circularly polarized luminescence measurements support chirality transfer from l-cysteine to the modified perovskite. The maximum absolute luminescence dissymmetry factors, |glum|, are 0.86 × 10–3 and 1.2 × 10–4 in the excitonic and Mn2+-emission regions, respectively.