Formation and Optical Properties of Fluorescent Gold Nanoparticles Obtained by Matrix Sputtering Method with Volatile Mercaptan Molecules in the Vacuum Chamber and Consideration of Their Structures

Abstract

This paper proposes a novel methodology to synthesize highly fluorescent gold nanoparticles (NPs) with a maximum quantum yield of 16%, in the near-infrared (IR) region. This work discusses the results of using our (previously developed) matrix sputtering method to introduce mercaptan molecules, α-thioglycerol, inside the vacuum sputtering chamber, during the synthesis of metal NPs. The evaporation of α-thioglycerol inside the chamber enables to coordinate to the "nucleation stage" very small gold nanoclusters in the gas phase, thus retaining their photophysical characteristics. As observed through transmission electron microscopy, the size of the Au NPs obtained with the addition of α-thioglycerol varied from approximately 2-3 nm to approximately 5 nm. Plasmon absorption varied with the size of the resultant nanoparticles. Thus, plasmon absorption was observed at 2.4 eV in the larger NPs. However, it was not observed, and instead a new peak was found at approximately 3.4 eV, in the smaller NPs that resulted from the introduction of α-thioglycerol. The Au NPs stabilized by the α-thioglycerol fluoresced at approximately 1.8 eV, and the maximum wavelength shifted toward the red, in accordance with the size of the NPs. A maximum fluorescent quantum yield of 16% was realized under the optimum conditions, and this value is extremely high compared to values previously reported on gold NPs and clusters (generally ∼1%). To our knowledge, however, Au NPs of size>2 nm usually do not show strong fluorescence. By comparison with results reported in previous literature, it was concluded that these highly fluorescent Au NPs consist of gold-mercaptan complexes. The novel method presented in this paper therefore opens a new door for the effective control of size, photophysical characteristics, and structure of metal NPs. It is hoped that this research contributes significantly to the science in this field.

Titanium oxide nanoparticle dispersions in a liquid monomer and solid polymer resins prepared by sputtering

“…Using this method, [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] robust NP size and composition control can be achieved in a single step process, such as the recently-reported synthesis of photo-luminescent metal NPs via sputtering in various liquid media. [18][19][20][21][22][23][24][25][26] Titanium dioxide, TiO 2 , NPs are important wide-bandgap materials used as UV-active photo-catalysts and various optical applications such as a UV block material in sunscreens, or to increase the refractive index of thin films 7,26 and polymers. 7,9 Modification of the electronic structure of TiO 2 via doping or introducing oxygen defects can narrow the bandgap and extend its energy harvesting applications towards the visible region.…”

Highly stable and blue-emitting copper nanocluster dispersion prepared by magnetron sputtering over liquid polymer matrix

“…On the other hand, physical processes [17][18][19][20][21][22][23][24][25][26][27] (cluster beam deposition, 17 sputtering [18][19][20][21][22][23][24][25][26][27] ) that do not need reducing agents, have been used to produce metal nanoclusters from the bulk metal source. The great advantage of these techniques over chemical reduction methods is the high purity of the nanoclusters that can be achieved, as the synthesis is done under vacuum conditions using a controlled atmosphere.…”

Silver sputtering into a liquid matrix containing mercaptans: the systematic size control of silver nanoparticles in single nanometer-orders

“…So far, several capturing matrices have been examined for the preparation of Au NPs by the matrix sputtering method and they can be categorized into (i) 6-mercaptohexyltrimethylammoniumbromide (6-MTAB) 15 and pentaerythritol tetrakis-(3-mercaptopropionate) (PEMP), 16 and (ii) propane-1,2,3-triol, 18 polyethylene glycol (PEG), 17,19,20 ionic liquids, 21,22 and pentaerythritol ethoxylate (PEEL). 16 Group (i) depends on the affinity of the mercapto group and can form very small (B1.3 nm) fluorescent Au NPs, while group (ii) depends mainly on the viscosity of themselves and forms rather large Au NPs (2-5 nm).…”