Er ³⁺ Mediated Multicolor Tuning of Luminescence in Piezoelectric Ca ₃ Ga ₄ O ₉ :Eu ³⁺ System: Non‐Pre‐Irradiated Mechanoluminescence and Multiplexed Photoluminescence

Abstract Photoluminescence (PL) and mechanoluminescence (ML), serving as core mechanisms of emerging intelligent luminescent materials, hold momentous promise for applications in information security, display technologies, and self‐powered sensing. However, conventional intelligent luminescent materials face critical limitations, including the difficulty in constructing multiplexing systems, dependence on ultraviolet (UV) pre‐irradiation, and constraints of monochromatic emission. To address these limitations, a series of Er ³⁺ mediated piezoelectric Ca ₃ Ga ₄ O ₉ :Eu ³⁺ samples is designed and developed, establishing a four‐wavelength‐excitation optical multiplexing platform, where each excitation source selectively activated distinct lanthanide energy transfer pathways while enabling tricolor PL tuning from orange‐red to yellow to green. Simultaneously, intriguing ML is also achieved, featuring non‐pre‐irradiation and multicolor (continuous red‐to‐green emission) tunability characteristics. More importantly, combining systematic experimental investigations and density functional theory calculations, the underlying mechanism of the ML has been elucidated as the synergistic contribution of triboelectric and piezoelectric effects. The developed Ca ₃ Ga ₄ O ₉ :Eu ³⁺ embellished by Er ³⁺ displayed intriguing potential application in grayscale analysis anti‐counterfeiting films, and self‐powered cipher lock system.