Enhanced Third‐Order Nonlinear Optics From In Situ Grown Lead‐Free Cs ₂ AgInCl ₆ Double Perovskite Nanocrystals in Chalcogenide Glass

Metal halide perovskites exhibit significant potential for optoelectronic applications due to their exceptional linear and nonlinear optical properties. However, the lead toxicity, coupled with the inherent thermal and photochemical instability of conventional lead‐based perovskites, restricts their utility in nonlinear photonic devices that require high‐energy excitation. Lead‐free metal halide double perovskites (MHDP), notably Cs 2 AgInCl 6 , have emerged as environmentally benign alternatives due to their superior structural stability. Nevertheless, systematic investigations of their third‐order nonlinear (TON) optical properties remain quite limited. In this work, we use chalcogenide glass (ChG) with intrinsically high TON to host in situ crystallized Cs 2 AgInCl 6 nanocrystals, creating a lead‐free nanocomposite material. Using Z‐scan and I‐scan techniques, the synthesized MHDP‐ChG composite was found to exhibit high nonlinear refractive indices, large two‐photon absorption coefficients, and low optical limiting thresholds at near‐infrared wavelengths. This work establishes a novel strategy for lead‐free, high‐TON‐performance MHDP materials and provides critical insights into their applications in nonlinear photonics.