Synthesis And Characterization Of Gold Nanocluster Emitting Strong Blue Luminescence

Gold nanoclusters have received much attention owing to their novel optical and electronic properties. Researches point out that Au particles, when their sizes decrease to comparable to the Fermi wavelength of an electron (usually <1.5nm), the quantum effect becomes apparent and the gold nanoparticles start to exhibit semiconductor electronic characteristics. The band gap begins to evolve, and luminescence will be observed under excitation.Compared to traditional fluorescent labels, Au nanoclusters have lots of advantages. Dye molecules are limited by photobleaching. Semiconductor nanocrystals, which have recently been introduced as labels, require toxic precursors and should be prepared under inert atmosphere at high temperature. On the contrary, the Au nanoclusters can be easily synthesized under mild conditions and show size-dependent emission. As an appealing optical label, Au nanoclusters have great potential to be used in imaging, biological labeling and LED related fields.To date, Au nanoclusters have been usually synthesized using Schiffrin method. Two key issues in this method are properly controlling the size of the Au particle and on the capping or protecting ligands bonded to the particle surface. In our study, also using Schiffrin method, we synthesized Au nanoclusters which were modified by a special dithiol ligand in reverse microemulsion, and astonished to observed novel fluorescent property. To the best of our knowledge, this is the first time the blue luminescence is observed from Au nanoclusters prepared by Schiffrin method, and the quantum efficiency is greatly enhanced to about 15%, which is more than 100-fold improvement over the best result reported.According to the detailed measurement results of our sample and compared to the reported results, we give explanations to the novel luminescence observed in our experiment. And we also give some suggestions on how to choose the appropriate ligand.