A Study On The Luminescent Property Of Gold Nanoclusters

Luminescent gold nanochisters(Au NCs)can be applied to biological imaging due to their excellent photo-stability,high emission rates,and good biocompatibility.Such materials have attracted great attention in the field of biology,chemistry,and materials science.Although people have made many important breakthroughs in exploring new methods for preparing Au NCs and improving its luminescence intensity,the luminescence quantum yield(QY)of luminescent Au NCs is still very low and the understanding of luminescence mechanism is still lacking.In this paper,Photoluminescence sPectra,transmission electron microscope(TEM),X-ray photoelectron spectroscopy(XPS)and X-ray absorption fine structure(XAFS)have been applied to study glutathione(GSH)protected Au NCs.The luminescence mechanism was was investigated.Two common methods:aggregation-induced emission and foriegn metal ions doping were applied to enhance the lxuninescence.The main research content includes the following three parts:(1)The effect of pH on the luminescence properties of during the preparation of Au NCs.In this study,we obtained Au NCs at different solution pHs with different luminescence properties.TEM results present that the size and aggregation degree of Au NCs are different at pH=1.6,pH=3.1,pH=11.9,pH=12.8 and there is no existence of Au NCs at pH = 7.1.Au NCs aggregate easily at acid conditions while disperse well at alkaline conditions.By the means of XPS and XAFS,we found that the acidic conditions are not conducive to nuclear growth of Au NCs except when the pH value of the solution close to PKa2 of GSH,while the alkaline conditions more conducive to nuclear growth of Au NCs,The electronic structure of Au NCs is affected by pH leads to different luminescence properties.(2)Effects of solution pH on the luminescence properties of as-synthesized Au NCs.In the experiment,GS-Au NCs synthesized at pH = 11.9 were used as standard sample.The change of the luminescence properties and the aggregation morphologies of Au NCs by constantly changing the pH of the solution(from alkaline to acidic to alkaline)were monitored.It was found that aggregation of CGS-An NCs in the solution enhance the luminescence intensity and leads to a blue shift in luminescence emission wavelength.However,the excessive aggregation of GS-Au NCs in the solution resulted in precipitation and decrease of luminescence intensity.(3)Effects of foreign metal ions doping on the luminescence properties of Au25(SG)i8.In this experiment,stable Au25(SG)18 was used as the research object and doped with Ag+,Pd2+ and Pt4+.When dopping ions are different,the luminescence is different:Ag+ doping will increase the luminescence of Axu25(SG)18 while Pd2+and Pt4?doping will make produce precipitate in the solution and weak the luminescence.In combination with XPS data,we found that foreign metal ions doping will change the valence state of Au,hence the change in luminescence properties.It is hoped that the results of these works can provide some help for the optimization synthesis method and the luminescence quantum yield improvement for Au NCs.