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Biomimetic optical devices based on cellulose nanocrystals with tunable structural colors have received significant attention recently. However, the limited ability to control multicolor separation beyond simple single‐color modulation restricts its practical applications. Here, a diversified multicolor separation strategy for the cholesteric phase cellulose composite (CPCC) is presented. The CPCC is prepared by integrating a high‐concentration self‐assembled hydroxypropyl cellulose with a cross‐linked poly(acrylic acid‐acrylamide) (P(AA‐AM)) network. By adjusting the cross‐linking degree of P(AA‐AM) in CPCC, Thermally induced multicolor separation is achieved from a homochromatic state at room temperature to multicolor patterned display at elevated temperatures. Furthermore, by utilizing the electric heating effect of conductive carbon oil, the multicolor separation under low voltage is achieved, and based on this, pixelated electro‐thermochromic displays are developed. Additionally, magneto‐thermal multicolor separation induced by introducing FeNi3 nanoparticles is investigated with efficient magnetic induction heating ability into CPCC. The multicolor separation effect is further improved by pixelated distribution of FeNi3 nanoparticles and adjusting the concentration of FeNi3 in each pixel. Finally, thermochromism, electro‐thermochromic, and magneto‐thermochromic functionalities are integrated into the CPCC, achieving advanced multilevel information encryption. This multilevel approach of controlling multicolor separation significantly enhances the functionality of nanocellulose in various potential photonic applications. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Low‐energy visible‐light‐activated carbon dots (CDs)‐based afterglow materials are difficult to realize due to the inherent aromatic carbon with high‐energy absorption and the lack of effective regulation. Here, a new strategy for visible‐light‐activated CDs is proposed by combining dual‐confinement and surface‐ionization, which employs NaOH for additional confinement and surface ionization of CDs in a single boric acid (BA) matrix. The comparison experiments show that: i) shifting the excitation from UV‐light to vis‐light is realized by enhancing the low‐energy surface states n→π* transition of the CDs by surface ionization of NaOH. ii) CDs are additionally protected by a more stable Na─O ionic bond after NaOH confinement, resulting in a brighter afterglow. iii) the energy gap (ΔEST) between the lowest singlet and triplet states is gradually shortened as increasing NaOH content, facilitating intersystem crossing, prolonging the lifetime of triplet excitons and efficiency. Further, vis‐light‐excited colorful afterglow powders are fabricated based on Förster Resonant Energy Transfer by combining the fluorescent dye 5‐carboxytetramethylrhodamine. Finally, advanced white‐light‐activated time‐resolved anti‐counterfeiting and intelligent traffic flashing signs are realized. The work may shed new light on the design of low‐energy‐activated afterglow materials and broaden the application scenarios in the daily lives of human society. [ABSTRACT FROM AUTHOR]