Achieving Ultra‐Brightness Green Light Source with Electro‐optical Conversion Efficiency up to 26.3% for Underwater Wireless Optical Communication

Abstract Using blue lasers to excite green‐emitting phosphors offers a compelling solution to address the “green gap” issue, providing a high‐brightness green light source for underwater wireless optical communication (UWOC). However, current green‐emitting phosphors show poor light conversion efficiencies or inadequate luminance saturation thresholds, impeding the development of brighter green light sources. Herein, the porous Lu 3 Al 5 O 12 :Ce phosphor ceramics are designed, which shows no change in quantum efficiency (82%) even after 6000 h of extended aging. This design results in a substantial improvement in light conversion efficiency (61.6%), luminous efficacy (286 lm·W⁻¹), and an exceptional luminance saturation threshold of 33 W·mm⁻ 2 , culminating in a maximum green light flux of 4720 lm. Moreover, the high‐directionality green light source device has been fabricated that achieves an illuminance of 6081 lx at a distance of 10 meters (15.0 W blue laser irradiation) with the electro‐optical conversion efficiency up to 26.3%, much higher than that using green laser directly (usually <20%). This setup enables long‐range underwater transmission of 65.3 meters with a peak data rate of 3.45 MHz, opening up new avenues for innovative advancements in UWOC technology.