Light Shutter Using ER Fluid Thin Films Dispersing ITO and ZnO Particles

Abstract

We have studied optical properties of alkylnaphthalene suspensions dispersing semiconductor ultra fine ITO (Indium Tin Oxide) particles or insulator ZnO particles to apply them to light shutter. The suspensions behave like ER fluids which show an increase in viscosity under an electric field. When the ITO or ZnO dispersions are sandwiched between glass plates coated by a transparent conducting film, the fluid films transmit visible light. Application 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 near infrared rays, whereas the transmittance in visible light region decreases with the electric field. On the other hand, the transmittance through the fluid film dispersing ZnO particles decreases in the wavelength region from visible light to near infrared rays with the electric field. These phenomena depend on the cluster size under the electric field and the solid concentration 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 optical absorption due to free carriers in ITO particles.