Light shutter using ER fluid thin films dispersing ITO and ZnO particles

We have studied optical properties of alkylnaphthalene suspensions dispersi ng semiconductor ultra tine ITO (Indium Tin Oxide) particles or insulator Z nO particles to apply them to light shutter. The suspensions behave like ER fluids which show an increase in viscosity under an electric field. When t he ITO or ZnO dispersions are sandwiched between glass plates coated by a t ransparent conducting film, the fluid films transmit visible light. Applica tion of the electric field in the direction of the light beam to the fluid film dispersing ITO particles shows an increase in the transmittance for ne ar infrared rays, whereas the transmittance in visible light region decreas es with the electric field. On the other hand, the transmittance through th e fluid film dispersing ZnO particles decreases in the wavelength region fr om visible light to near infrared rays with the electric field. These pheno mena depend on the cluster size under the electric field and the solid conc entration of the suspensions. We can explain the results in terms of light scattering due to ITO or ZnO clusters formed in the electric field and opti cal absorption due to free carriers in ITO particles.