Terbium oxide exhibits significant potential in optoelectronics sensing; yet, its limited solubility in silica severely restricts the active concentration of Tb-doped silica materials. This study presents an efficient, and reproducible approach for aluminum oxide oxygen evolution to attain high-concentration Tb³⁺ nanoparticle doping. Dense and continuous Tb₂O₃:Al₂O₃ films with varying vertical spatial distributions were fabricated on silica substrates utilizing atomic layer deposition (ALD) technology. X-ray photoelectron spectroscopy and photoluminescence analysis demonstrated that the Al₂O₃ generated additional O²⁻ active sites, augmenting Tb(4f)-O(2p)-Al(2p) covalent orbital coupling, thereby substantially enhancing structural stability, improving the luminescence performance of Tb₂O₃, and promoting valence state reduction. A Tb/Al co-doped silica optical fibers were fabricated and utilized for weak magnetic field sensing. The optical fiber demonstrated a compact structure and excellent stability, with an unparalleled solid-state doped fiber sensitivity of 45.60 nT/√Hz. The improved ALD deposition facilitates effective Tb-O-Al coupling, showcasing significant potential for the advancement of next-generation integrated photonic sensors.