Author Description

The Christiansen Effect occurs when the refractive index (n) of a given material matches that of its surrounding medium at a particular wavelength, leading to a transmission window. When air is chosen as the medium, the Christiansen Effect is observed when the refractive index of a given material passes through n =1 at a specific wavelength (λc), and subsequently produces a transmission at wavelength λc. In general, materials that exhibit a refractive index of n =1 in the near infrared are of particular interest for a variety of glass optics and imaging applications. In this study, we demonstrate for the first-time the realization of the Christiansen effect at the surface of bulk ITO materials, i.e. the realization of a refractive index of n =1 at specific wavelengths within the near infrared (NIR) and shortwave infrared (SWIR) regions. It was found that conductivities of greater than a few hundred thousand S/m is required for desired optical properties. Thermal treatment of the bulk ITO wafers was also carried out to study its impact on the conductivity and tunability of the wavelength of transmission. Additionally, we hypothesized that the Christiansen effect should also be observed in suspensions containing ITO particles. This was tested by milling ITO target wafers into powders and subsequently suspending the particles in a suitable solvent. Unfortunately, initial evaluation of ITO suspensions did not manifest the Christiansen effect. We suggest that this was due to inadequate Sn substitution in the milled nanoparticles, relative to the bulk material. We hypothesize that Sn substitution occurred only at the boundaries between the pressed In2O3 and SnO2 particles, and that after the target wafer was milled, the individual In2O3 and SnO2 particles did not exhibit the sufficient conductivity for producing an n =1 wavelength.