Photobleaching of silicon-related bismuth active centers originating from pseudo-Jahn-Teller effect-driven structural distortion.

Advancing AI and 6G technologies escalate bandwidth demands, driving interest in bismuth-doped fibers (BDFs) for ultra-broadband amplification. However, photobleaching (PB) of silicon-related bismuth active centers (BAC-Si) limits deployment, a process traditionally attributed to extrinsic defect-mediated electron transfer. Here, bismuth-erbium co-doped fibers (BEDFs) were irradiated by a 248-nm laser over 0-100,000 pulses to control defect transformation. Irradiation altered BAC-Si concentration and microenvironment but did not exacerbate the PB effect under 830-nm pumping. Consequently, we propose that PB originates from intrinsic structural distortion via excited-state (Es) vibronic coupling, characteristic of the pseudo-Jahn-Teller effect (PJTE), unifying PB initiation and modulation mechanisms.