A suspended particle device adapted for controlling the transmission of electromagnetic radiation has become an area of considerable focus for smart window technology, due to their desirable properties such as instant and precise light control and cost-effectiveness. Here, we demonstrate transparency tunable device in response to electric stimuli using spherical colloidal nanoparticles and their assemblies. The observed transparency is dynamically tunable in response to simple and relatively small (1-5 V) external electrical voltage with increased transparency when applied voltage increases. The observed transparency change is attributed to structural ordering of nanoparticle assemblies and thereby to modified photonic band structures, confirmed by finite-difference time-domain simulations of Maxwell’s equations. Interestingly, in addition to transparency, structural colorations and their dynamic tunability are demonstrated using α-Fe2O3/SiO2 core/shell nanomaterials, resulting from the combination of inherent optical properties of α-Fe2O3/SiO2 nanomaterials and coloration due to their tunable structural particle assemblies in response to electric stimuli. The use of colloidal nanoparticles along with variation in the material composition, the particle size, and device thickness provided multiple pathways to tune the transparency as well as color spectrum.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.