Assembly of CQDs/mesoporous SiO2/VO2 composites with wide optical response and abnormal phase transition temperature

The rapid reversible metal-insulator transition (MIT) of vanadium dioxide (VO2) between the monoclinic and rutile phase brings about an abrupt change in optical properties. Until now, most researches focused on regulating near-infrared spectra and lowering phase transition temperature (Tc) while the optical response in the region of UV–vis and high Tc for VO2 are ignored. Herein, carbon quantum dots (CQDs) were introduced into mesoporous SiO2 microspheres and then CQDs/mesoporous SiO2/VO2 composites were synthesized in situ to expand the optical response and Tc range of VO2. Water bath time and annealing temperature have important influences on the morphologies and properties of as-prepared composites. The prolongation of hydrothermal time could promote the formation of VO2 nanoparticles. After annealing, the Tc for as-prepared CQDs/mesoporous SiO2/VO2 composites was in the range of 80.5–93.6 °C. The CQDs/mesoporous SiO2/VO2 composites exhibited broad and strong UV–vis absorption in the range of 200–1200 nm, and the sample prepared under the conditions of a water bath time of 3 h and annealing temperature of 550 °C had the maximum luminous transmittance (Tlum = 64.665 %) as well as the highest solar modulating ability (ΔTsol = 2.42 %). Therefore, the wide range of optical response and abnormal Tc besides typical phase transition behaviors for CQDs/mesoporous SiO2/VO2 composites have a potential application in the field of optical devices related to UV–vis region and high temperature environments.