Cross‐Linkable Room‐Temperature Phosphorescent Polymer Blends With Ultrawide Modulus Tunability

Pure organic room‐temperature phosphorescence (RTP) polymers have attracted considerable attention for their promising applications in information encryption, anti‐counterfeiting, and flexible optoelectronics. Herein, we report a strategy combining physical blending and in situ covalent cross‐linking to fabricate processable RTP polymer blends with ultrawide mechanical tunability. Flowable precursors are first prepared by dispersing carbazole‐based phosphor‐doped polystyrene (PS) into polyethylene glycol (PEG), followed by cross‐linking of terminal hydroxyl groups to form a three‐dimensional polyurethane network that provides an excellent oxygen barrier and shape fixation. The optimized system exhibits bright yellow RTP with afterglow durations of 1.7–5.5 s, representing a 2–5‐fold enhancement compared with non‐cross‐linked systems. Impressively, Young's modulus can be precisely tuned over 9 orders of magnitude from ∼10 −1 to ∼10 8 Pa. This work provides a universal and scalable route for developing moldable, mechanics‐tunable RTP polymers for advanced optical and anti‐counterfeiting applications.