Ecofriendly Perovskites with Giant Self‐Defocusing Optical Response

The full optical control of light using sustainable green technologies is one the incipient challenges Photonics community. There are, however, few materials able to provide a significant nonlinear refractive index change under small enough intensities (< 1 GW cm−2), and, more importantly, allowing external magnitude and sign their response. This manuscript demonstrates that Cs2SnI6 lead-free nanocrystals (NCs) present an extraordinary self-defocusing response not yet observed up now in any material. Despite its complex structural form, these NCs are fully characterized here, both experimentally theoretically, revealing giant negative Δn = −0.05 proper illumination conditions. tuned with intensity, concentration solvent, propagation distance leading crossover where media transforms self-focusing +0.002. These results can fascinating opportunities sensing light–matter interactions for future ecofriendly photonic technology.