Bright Cyan Circularly Polarized Luminescence and Efficient Second Harmonic Generation in Zero-Dimensional...

Chiral metal halides featuring circularly polarized luminescence (CPL) have drawn considerable attention due to their promising applications in imaging, sensing, and photonics. However, such materials largely rely on chiral organic cations, and technically significant cyan CPL remains out of reach. Here, we report an enantiomeric pair of zero-dimensional chiral silver halides, P/M-(MTP)₂AgI₃ (MTP = methyltriphenylphosphonium), constructed from achiral MTP⁺ cations and distorted triangular-planar [AgI₃]^2- units. Further intentional doping with copper(I) ions not only suppresses nonradiative recombination but also introduces additional emissive centers, leading to photoluminescence quantum yield enhanced from 0.8% to near unity and enabling bright cyan CPL with a large dissymmetry factor g_lum of 1.3 × 10^-2. Moreover, the intrinsic non-centrosymmetry of this material enables efficient second harmonic generation, together with a high laser-induced damage threshold of 52.6 mJ cm^-2. This study offers new insights into the design of chiral metal halides with rich chiroptical and nonlinear optical effects.