Reversible photochromic W18O49: Mechanism revealing and performance improvement for smart windows

W18O49 has widely used in photothermal application and photocatalyst due to its strong Localized Surface Plasmon Resonance (LSPR) effect and unique oxygen-deficient structure. In addition, the unstable structure and easily changed valence state of W5+ make W18O49 potentially photochromic. However, the generally synthesized blue W18O49 particles was in a saturated colored state, delivering a great challenge in exploring its photochromic features, which thus have seldom been studied. Herein, we found that the bleached W18O49 obtained by mild-heating the solvothermal-synthesized blue W18O49 nanoparticles in air had considerable reversible photo-chromic feature, which can be colored in 1 min under UV irradiation. The photochromic mechanism of W18O49 was revealed through the XRD, XPS and FTIR results. The chromic process was mainly attributed to the changed W5+ content under different conditions. The photochromic performance was systematically investigated on the W18O49-based film and which can be significantly improved by Ti doping. Finally, the great potential of the films in the energy-saving smart windows application has verified, and a 10 at.% Ti-doped W18O49 film delivered outstanding optical performance with luminous transmittance (Tlum) of 87.53% and solar energy modulation efficiency (& UDelta;Tsol) of 30.13%.

Automated summary

W18O49 shows strong Localized Surface Plasmon Resonance (LSPR) effect and unique oxygen-deficient structure, making it widely used in photothermal application and photocatalyst. The photochromic feature of W18O49 has seldom been studied due to the challenge of exploring its features in the saturated colored state. However, the researchers found that the bleached W18O49 obtained by mild-heating the synthesized blue W18O49 nanoparticles in air had considerable reversible photochromic feature, which has great potential in energy-saving smart windows application.