Large and constant absorption coefficient in NbxTi1-xO2 thin films throughout the visible range

We investigated the optical absorption properties of NbxTi1-xO2 thin films, a solid solution combining the reduced titanium and niobium oxide phases TiO2 and NbO2. The optical absorption properties of NbxTi1-xO2 thin films prepared by pulsed laser deposition at 600 degrees C were shown to be large in magnitude at an almost constant value of approximate to 17 mu m(-1). Because this large absorption coefficient is nearly independent of incident photon energy in the visible range (400-700 nm), the Nb(x)Ti(1-)xO(2) thin films appear optically black. Flat and homogenous, optically black coatings like these are desirable for color isolation in flat panel displays. The origin of flat wavelength dispersion in NbxTi1-xO2 is the coexistence of semiconducting absorption and metallic light absorption mechanisms. Localized Nb-Nb dimers in the metallic NbxTi1-xO2 phase open an optical band gap which gives rise to semiconducting behavior. We show here that reduction results in strong visible light sensitization in normally transparent Nb-Ti oxides.