One-step hydrothermal synthesis of rare earth/W-codoped VO2 nanoparticles: Reduced phase transition temperature and improved thermochromic properties

As a reversible thermochromic material, vanadium dioxide (VO2) is a promising candidate for smart window applications. The trade-off between the integrated visible transmission (Tlum) and the solar modulating ability (ΔTsol), as well as the high phase transition temperature (τc~68 °C) are regarded as the main obstacles for practical applications of pure VO2 nanomaterials. The combination of both high τc reducing efficiency of W and improving Tlum/ΔTsol properties of RE (rare earth: Eu, Tb), herein lies the purpose of RE/W-codoping to enhance the thermochromic performance. The RE/W-codoped VO2 nanoparticles were synthesized under hydrothermal conditions, and exhibited grain size of less than 100 nm. The smart window which was fabricated by coating RE/W-codoped VO2 nanoparticles onto glass, exhibits a thermochromic performance with a combination Tlum= 40%, ΔTsol= 6.3%, τc= 40.8 °C or Tlum= 63%, ΔTsol= 3.6%, τc= 31.9 °C, indicating the largely reduced absorption compared with the single W doping. Under the RE/W-codoping conditions, it was found that the ionic radius of the RE3+ cations controlled the crystallinity of the VO2 particles and the electron/hole carrier counteraction as well as the competition between the strain and the hole carrier played a vital role in modulating the τc of the VO2 products. The findings should be meaningful for investigating the codoping mechanisms for VO2 nanomaterials.NRF (Natl Research Foundation, S’pore)MOE (Min. of Education, S’pore)Accepted versio