Lifetime modulation of graphene oxide film by laser direct writing for the fabrication of micropatterns

Abstract

The strong, broad and tunable fluorescence emission of graphene oxide (GO) has shown the exciting optical applications in many areas, such as fluorescence imaging in living cell, high sensitive detection of heavy metal ions, and the fabrication of optoelectronic devices. However, the intrinsic heterogeneous fluorescence intensity resulting from the variability in the power density of excitation laser and the non-uniform thickness of GO film, hinders its further applications in the micropatterning, information storage and display technology, which requires homogeneous fluorescence emission. In contrast to the fluorescence intensity, the fluorescence lifetime of GO is determined by the intrinsic nature of chromophores, rather than the film thickness or excitation power density. Here we report that the fluorescence lifetime is homogeneous for GO film, which eliminates the anisotropic optical properties of GO film. By reducing the GO film through the irradiation from a 405 nm continuous-wave laser at a certain power density on a home-built scanning confocal microscope, we find that the lifetime can be precisely modulated by controlling the duration of laser irradiation. It is determined that the lifetime gradually decreases with the increase of duration. As reported in the previous researches, the GO fluorescence originates from the graphene-like confined sp2 clusters and sp3 domains consisting of oxygen-containing functional groups, where the lifetime of sp3 domain is about 1.4 ns, and that of sp2 domain is 0.14 ns. During the photoreduction, the long-lived sp3 domains will decrease or convert into short-lived sp2 domains, resulting in the decrease of lifetime. Hence, by controlling the reduction degree or the ratio of the two domains, the lifetime of GO film can be determined. More importantly, the lifetime distributions of the reduction areas are very narrow, leading to a relatively homogenous background. The precise manipulation of lifetime can be used to fabricate micropatterns with high contrast. Combining with laser direct writing with features of maskless, facile processing ability and high spatial resolution, many versatile micropatterns, such as quick response code, barcode, graphic, alphabet, and numbers can be readily created based on the modulation of fluorescence lifetime. By using three optimized durations of laser irradiation, three distributions with narrow widths are obtained. Based on this processing, the micropatterns with three colors are determined, which indicates that the multimode optical recording can be created on the GO film based on the modulation of fluorescence lifetime. Furthermore, the multilayer micropatterns are also created. The robust and versatile micropatterns with film-thickness and excitation-power-independent features show their promising applications in electronics, photonics, display technology and information storage.