Abstract
An intense photoluminescence emission was observed from noble metal nanoclusters (Pt, Ag or Au) embedded in sapphire plates, nucleated by MeV ion-implantation and assisted by an annealing process. In particular, the spectral photoluminescence characteristics, such as range and peak emission, were compared to the behavior observed from Pt nanoclusters embedded in a silica matrix and excited by UV irradiation. Correlation between emission energy, nanoclusters size and metal composition were analyzed by using the scaling energy relation EFermi/N1/3 from the spherical Jellium model. The metal nanocluster luminescent spectra were numerically simulated and correctly fitted using the bulk Fermi energy for each metal and a Gaussian nanoclusters size distribution for the samples. Our results suggest protoplasmonics photoluminescence from metal nanoclusters free of surface state or strain effects at the nanoclusters-matrix interface that can influence over their optical properties. These metal nanoclusters present very promising optical features such as bright visible photoluminescence and photostability under strong picosecond laser excitations. Besides superlinear photoluminescence from metal nanoclusters were also observed under UV high power excitation showing a quadratic dependence on the pump power fluence.
Highlights
On the other hand, scarcely systematic investigation has been done to synthesize and understand the optical properties of sub-nanometer metal NCs embedded in dielectric inorganic matrices
To understand the photophysics of metal NCs, a simple scaling energy relation, EFermi/N1/3, where EFermi is the bulk metal Fermi energy and N the number of atoms in the clusters, is commonly used to provide an approximated description of the energy emission from Au NCs32 and it is derived from quantum confinement effects in the Jellium model approximation
For Au NCs embedded in a silica matrix a decrease in energy emission with the number N of atoms in the NCs has been reported as predicted by Jellium model; their energy emissions do not match using the Au bulk Fermi energy[28]
Summary
Scarcely systematic investigation has been done to synthesize and understand the optical properties of sub-nanometer metal NCs embedded in dielectric inorganic matrices. For Au NCs embedded in a silica matrix a decrease in energy emission with the number N of atoms in the NCs has been reported as predicted by Jellium model; their energy emissions do not match using the Au bulk Fermi energy[28] Deviation from this scaling relation can be attributed to the presence of surface state or strain effect that actively participate in the electronic transitions that give rise to PL emissions. Metal NCs can have different luminescent properties depending on the host matrices and a lot of research must be done in order to find valuable properties and optimal synthesis condition to meet particular applications With these motivations, in this work we report for the first time bright photoluminescence from noble metal NCs embedded in sapphire matrices synthesized by MeV ion-implantation technique. Metal NCs in sapphire and silica were formed by using similar condition of synthesis, i.e. similar ion-implantation energies and annealing temperatures, and this can be addressed to combine them in the same sapphire matrix to obtain a solid state nano-source of white light emission
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