Polychrome Stimuli‐Responsive Afterglow Membrane Tuned by Coordination Field Effect for Humidity Visual Monitoring

Abstract Phosphorescence‐based optical detection offers considerable potential for highly sensitive humidity monitoring but is impeded by limited visual resolution and challenges in reuse. Here, an energy transfer strategy is proposed to regulate phosphorescence through crystalline hydrate‐induced coordination field variations, enabling reversible humidity monitoring with distinct afterglow colors. A super‐hydrophilic, self‐supporting porous polyethersulfone membrane, encapsulating carbon dots‐dyes@silica (CDs‐Dyes@SiO 2 ) multicolor phosphorescent nanoparticles and anhydrous CoCl 2 , is fabricated using a simple phase‐transfer method. Dynamic phosphorescent visualization of humidity is achieved through the selective absorption of phosphorescent emission from CDs‐Dyes@SiO 2 , driven by the reversible coordination field transitions reflected in the UV–vis absorption peak shifts between CoCl 2 and CoCl 2 ·nH 2 O. The ultra‐hydrophilic afterglow membrane, with its rapid water vapor capture and enrichment ability, sensitively indicates relative humidity levels from 21.6% to 89.0% by visual color discrimination at room temperature. Furthermore, the color‐recognizable afterglow membrane is effectively employed as a real‐time and high‐resolution humidity sensor for applications in human and plant health management.