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
- Publication date
- Publisher
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