Nanostructured WO3 films synthesized on mica substrate with novel photochromic properties

Herein, it is reported that ordered tungsten oxide WO3 films have been prepared on the natural mica substrate by a simple hydrothermal method. Under the mild hydrothermal environment, the mica substrate can still induce a WO3 compact layer with good epitaxial texture. The influence of precursor concentrations on the films are further discussed that changing precursor concentrations doesn't change the films' composition, but makes a great influence on the films' morphologies and photochromic properties. The XRD result reveals that the films are hexagonal WO3. As the precursor concentration (Cp) increases from 0.01 M to 0.14 M, the morphology of the films changes from six-pointed star nanostructure to lush grass nanostructure, irregular nanorods nanostructure, finally granule nanostructure and uneven flaky particles. The samples obtained with Cp = 0.10 M and Cp = 0.14 M absorb almost 100% of the incident UV light. Interestingly, a kind of novel absorption in the NIR range of 800-850 nm is observed with Cp = 0.10 M. The absorption range moves to the vis-NIR range of 680-850 nm when increases the Cp to 0.14 M. In this process, the sample obtained with Cp = 0.14 M exhibits the optimized photochromic performance due to the high crystallinity and huge exposed surface area.