Optical response of inverse opal-like structures prepared from titanium dioxide with copper and nickel dopants

Abstract

Inverse opals, as ordered macroporous structures, are widely used due to their interesting optical response. The addition of metal oxide dopants increases their optical absorption. However, with heavy dopant concentrations, the doped inverse opal is affected by structural damage and higher solid volume fractions. In this work, the effect of dopant concentration on inverse opals was investigated by doping copper and nickel into TiO2. The inverse opal-like structure was prepared by infiltrating TiO2 sol-gel into polystyrene microsphere opal templates and then baking at 500°C. The polystyrene opal templates were constructed by self-assembly convective deposition with vibration assistance. The fluorescence emission from Cu d-states and defect states in doped TiO2 structures were studied. The emission for copper-doped TiO2 was observed at a wavelength of 520nm with excitation at 410nm. Although the characteristic emission of the dopants was readily observed, the overall fluorescence intensity of the doped TiO2 layer was much lower than that of the undoped TiO2 structure. Chemical compositions investigated by x-ray photoluminescence showed that the dopants disturbed the TiO2 bonds and created defect states. The reflection of the fabricated film under visible wavelength was stronger at higher dopant concentrations. These results are explained because the inverse opal has a higher solid content and the higher reflectivity is likely to be due to the rutile phase of TiO2.