A General Strategy for Ultralong Phosphorescent Photonic Crystals, Achieving Thermal Sensitive, Tri‐State Optically Compensated Gels

Abstract Integration of photoluminescence (PL), especially the long‐lived room‐temperature phosphorescence (RTP), into periodic submicron structures to build multi‐optical morphology photonic crystals (PCs) is a trend for future optical devices but has proven extremely challenging. Here, an emerging general strategy for fabricating three‐optical morphology (tri‐state) SiO₂‐based PCs by calcining monodisperse SiO₂ nanospheres with carbon dots (CDs) encapsulated inside is reported. The resulting phosphorescent SiO₂ nanospheres are unaffected by the type of surface defects or heteroatom doped in CDs, but rely on C─Si covalent bonds to stabilize the excited triplet state (T₁). The high degree of integration of chemiluminescent molecules and physical unit arrays offers the possibility of PCs with RTP emission in various physical morphologies. The assembled tri‐state PCs exhibit vivid structural colors, blue PL and green RTP under different light stimulation. Additionally, an intelligent thermal‐responsive optically tri‐state PC gel is successfully fabricated by self‐assembly of colloidal particles in suspensions. The optical signals (including structural color, transmittance, PL, and RTP) of the gels exhibit complementary properties regulated by temperature in the reflection and transmission modes. The general strategy and multifunctionality of these tri‐state PCs and gels open new avenues for applications in decorative coatings, tri‐morphology recyclable smart windows, and information encryption.