Convenient Production of Photothermal Recycling Phosphorescent Materials from Cellulose and Lignin

Abstract Developing recyclable room‐temperature phosphorescent (RTP) films using ultrafast fabrication techniques remains a critical yet challenging objective. With this research, we developed an RTP film (Cell‐Lig) through ethanol‐induced phase transition, achieving solid film formation within 1 s from ionic liquid (1‐butyl‐3‐methylimidazolium chloride, [Bmim]Cl) solutions of cellulose and lignin. The phase transition also generated a confined rigid environment for Cell‐Lig, activating thickness‐ and temperature‐dependent green RTP emission from the incorporated lignin. Furthermore, red afterglow emission using an energy transfer mechanism was realized by incorporating rhodamine B (RhB). The inherent photothermal activity of lignin endowed Cell‐Lig with easy recyclability using light‐controlled phase transitions. Under irradiation, photothermal evaporation of residual ethanol triggered liquefaction (solid‐to‐liquid transition), while ethanol reintroduction facilitated instantaneous hardening. Remarkably, the initial RTP performance was maintained over six recycling cycles. Capitalizing on these attributes, Cell‐Lig was successfully used for advanced coating and security applications.