Rigid polymer matrix enables direct red afterglow from rhodamine dyes without energy transfer

Abstract Room‐temperature phosphorescence (RTP) materials have garnered significant attention for their unique optical properties in information encryption and bioimaging. While triplet‐singlet Förster resonance energy transfer strategies have been employed to endow traditional fluorescent dyes with afterglow, they suffer from complex multi‐component systems and strict donor‐acceptor matching requirements. Here, we report a novel and universal strategy to achieve direct, long‐lived RTP emission from commercial rhodamine dyes (rhodamine B (RhB), SRB, Rh6G, Rhodamine 110) by simply doping them into a newly synthesized rigid phosphorus‐containing polymer (DOBP). The robust rigid network of DOBP effectively immobilizes the dye molecules and shields them from oxygen, drastically suppressing the non‐radiative deactivation of triplet excitons. Remarkably, the DOBP‐RhB film exhibits an intense orange‐red afterglow with a lifetime of 203.29 ms under ambient conditions, which is approximately 29 times longer than that of RhB at 77 K, demonstrating superior confinement over cryogenic conditions. This strategy produces tunable afterglow colors ranging from orange‐red to orange‐yellow without any complex energy transfer processes. This work provides a facile, practical route to transform commercially available fluorescent dyes into high‐performance RTP materials, addressing the challenge of color monotonicity and paving the way for advanced anti‐counterfeiting and multi‐level information encryption applications.