  Optical materials with colour-changing abilities have been explored for
display devices, smart windows, or modulation of visual appearance. The
efficiency of these materials, however, has strong wavelength dependence, which
limits their functionality to a narrow spectral range. Here, we report
graphene-based electro-optical devices with unprecedented optical tunability
covering the entire electromagnetic spectrum from the visible to microwave. We
achieve this non-volatile and reversible tunability by electro-intercalation of
lithium into graphene layers in an optically accessible device structure. This
unique colour-changing capability, together with area-selective intercalation,
inspires fabrication of new multispectral devices, including display devices
and electro-optical camouflage coating. We anticipate that these results
provide realistic approaches for programmable smart optical surfaces with a
potential utility in many scientific and engineering fields.
