Polymer-regulated crystallization enables scalable, high-performance heterostructured perovskite luminescent...

Fiber-based visual signaling can transform fabrics into distributed optical information systems, enabling real-time, large-area human-environment interaction. Perovskites are promising emitters for such systems owing to their narrow emission bandwidth and tunable optoelectronic properties. However, the intrinsic coupling between crystallization and filament formation in conventional fiber fabrication fundamentally constrains crystal growth pathways, limiting access to precise crystal engineering in luminescent fibers and thereby restricting emission purity, structural uniformity, and system-level functional integration. Here we report the first geometric transformation strategy for perovskite luminescent fibers, decoupling crystal growth from fiber formation and greatly expanding the crystallization-control toolbox for fiber-integrated perovskites. Enabled by weak-coordination polymer-regulated colloid chemistry and crystal growth, the fibers deliver ultrapure green emission at 522 nm with a full-width at half-maximum of 19 nm and International Commission on Illumination (CIE) of (0.11, 0.79), comparable to the best values reported for CsPbBr₃-based luminescent fibers. The fibers retain bright luminescence under bending, ultraviolet exposure, machine washing, artificial-sweat treatment, simulated-seawater treatment and thermal stress, while exhibiting trace-level Pb release far below the World Health Organization guideline value for lead in drinking water. This strategy establishes a general and scalable route that can support kilometer-scale production of functional fiber. More importantly, the deliberate integration of two polymers with a mechanical modulus mismatch exceeding two orders of magnitude into a single heterostructured fiber confers multifunctionality through structural design, including robust underwater emission and deformation visualization, which is further demonstrated through a bandage-integrated wireless optical readout system. This work establishes a general paradigm for embedding crystallization-engineered optoelectronic functionalities into continuous fiber architectures, redefining textiles as scalable platforms for smart, visually interactive optoelectronic systems.