Producing Sustainable Multicolor Room‐Temperature Phosphorescence From Natural Phenolics via a Precipitated Salt Confinement Strategy

Developing sustainable room‐temperature phosphorescent (RTP) materials from natural sources is highly desirable, yet achieving color‐tunable and long‐wavelength RTP without foreign sensitizers is difficult. Here, we report a facile precipitated salt confinement strategy to activate efficient and color‐tunable RTP from ellagic acid (EA). By controlling the deprotonation degree of EA and conducting in situ co‐precipitation with magnesium ions, a rigid matrix is constructed, resulting in EA@Mg(OH) 2 composites that exhibit phosphorescence color progressively shifting from green to orange (545–590 nm) with lifetimes up to 687.19 ms. Density functional theory (DFT) calculations reveal that deprotonation narrows the emitter's energy gap and strengthens its binding to the inorganic matrix, cooperatively enabling the color shift and the suppression of non‐radiative decay. We further demonstrate applications in multi‐color afterglow paper, textiles, and anti‐counterfeiting patterns, establishing a novel paradigm for creating high‐performance, sustainable RTP materials from abundant natural resources.