Light modulation of nanostructured alumina anodic oxide thin film on sapphire

The optical behaviour of nanostructured nanoporous alumina anodic oxide thin film (AAOF) on sapphires was investigated. The AAOF was intentionally nanostructured by varying the nanopore diameters, as a result, the distance between neighbour pores decreased. The resultant nanostructured nanoporous patterns cause super-paramagnetism and the excited photoluminescence splits into two wavelengths of near blue and green peaks. This light modulation could be related to the super-paramagnetic magnetisation of the patterns upon in nanoscale. With increasing the nanopore size by the reaming method, the super-paramagnetic susceptibility first decreases and then increases. Once the super-paramagnetic susceptibility deviates from that of the as-received AAOF, the green peak would be excited. On the other hand, strong super-paramagnetism facilitates excitation of the blue peak.