<p>As a fundamental element in integrated photonic systems, the functionality of polymer-based waveguide amplifiers is primarily determined by the optical properties of the active material. More precisely, the amplification bandwidth establishes the working spectral region of the photonic circuit. Consequently, developing gain media that feature both broad bandwidth and high gain has emerged as a critical challenge in the field. The performance of this gain medium is fundamentally determined by rare-earth-ion-doped crystals, as the emission spectrum of these crystals ultimately dictates the achievable gain bandwidth. In this study, Y₂O₃: Yb, Er, Ce crystals with emission peaks covering the entire S + C + L band were prepared. In Y₂O₃ crystals with low crystal field symmetry, the ⁴I₁₃/₂ and ⁴I₁₅/₂ levels of Er³⁺ ions were observed to undergo severe splitting, which in turn allows for effective broadening of the operational bandwidth. Fluorescence analysis reveals that the broadband emission from Er³⁺ ions stems from the pronounced energy level splitting caused by the crystal field effect. When irradiated with a 980&#xa0;nm laser, the emitted peak coverage from these Y₂O₃: Yb, Er, Ce crystals spans the complete S + C + L spectral range, demonstrating broadband optical amplification properties. Incorporation of Ce³⁺ substantially improved the emission strength within these crystals across the S + C + L spectral region. Given their remarkable broadband luminescence characteristics across the S + C + L spectral range, Y₂O₃: Yb, Er, Ce materials represent promising candidates for gain media in next-generation polymer-based optical amplifiers.</p>