Underwater Wireless Optical Communication Enabled by Self‐Crystallized Luminescent Nanocrystals in Borogermanate Glass

Underwater wireless optical communication (UWOC) demands light sources that simultaneously offer cyan emission (480–490 nm), high photoluminescence quantum yield (PLQY), and long‐term stability. However, current approaches face a persistent trilemma involving the wavelength mismatch of commercial light sources, poor stability of emitters, and significant scattering losses. Herein, we design a phase‐transition‐engineered borogermanate glass that enables the controlled self‐crystallization of CsPbCl 1.5 Br 1.5 perovskite nanocrystals (PNCs). A reduced crystallization activation energy promotes the in‐situ formation of PNCs, while the rigid B‐O‐Ge glass network confines growth of ultra‐small nanocrystals, achieving a PLQY of 54.5% with emission centered at 484 nm, well‐matched to the optical transmission window of water. When integrated with ultraviolet LED chips, the resulting glass achieves UWOC over a distance of 1.6 meters in natural lake water, tripling the transmission distance previously reported for perovskite‐nanocrystal‐based color‐conversion materials in UWOC, and enabling real‐time audio transmission. This study not only provides mechanistic insights into the crystallization kinetics of hybrid glass‐PNC systems but also offers a strategy for constructing stable and efficient underwater optical emitters.