Au–Ag nanoalloy molecule-like clusters for enhanced quantum efficiency emission of Er³⁺ions in silica

Abstract

The occurrence of a very efficient non-resonant energy transfer process forming ultrasmall Au-Ag nanoalloy clusters and Er(3+) ions is investigated in silica. The enhancement of the room temperature Er(3+) emission efficiency by an order of magnitude is achieved by coupling rare-earth ions to molecule-like (Au(x)Ag(1-x))N alloy nanoclusters with N = 10-15 atoms and x = 0.6 obtained by optimized sequential ion implantation on Er-implanted silica. For comparison, AuN nanoclusters obtained by the same approach and with the same size and numerical density showed an enhancement by only a factor of 2 with respect to pure Er emission, demonstrating the beneficial effect of using nanoalloyed clusters. The temperature evolution of the energy transfer process is investigated by photoluminescence and exhibits a maximum efficiency at about 600 °C, where the clusters reach the optimal size and the silica matrix completely recovers the implantation damage. The nanoalloy cluster composition and size have been studied by EXAFS analysis, which indicated a stronger Ag-O interaction with respect to the Au-O one and a preferential location of the Ag atoms at the nanoalloy cluster surface.

Emission Efficiency Enhancement of Er3+ Ions in Silica by Near‐Field Coupling With Plasmonic and Pre‐Plasmonic Nanostructures

“…On the other hand, when the samples are annealed at higher temperatures (i.e., 700 and 800 °C), despite the reduction of implanted‐induced defects, the growth of Ag NPs large enough to support a strong LSPR quenches the Er 3+ luminescence. Therefore the experimental findings suggest that the enhancement of the Er 3+ emission at 1.54 μm is due to the sensitization effect of Ag pre‐plasmonic clusters with a mechanism similar to the one recently demonstrated for Au and AuAg sub‐nanometric clusters . When noble metal nanoclusters are in close proximity ( nm) to Er ions, they are able to absorb the incident light through broad‐band interband transitions (with an absorption cross‐section much higher than the Er 3+ one) and efficiently transfer the energy to the nearby Er ions via a short‐range non‐radiative mechanism …”

“…This is a further indication that the excitation process is mediated by the broad‐band absorption of the Ag pre‐plasmonic clusters whose excitation efficiency is proportional to the cluster interband absorption (higher at 476 nm than at 488 nm − see Figure ). Moreover, it is worth noting that the contribution of direct Er 3+ excitation to the PL intensity at 1540 nm when the sample is excited at can be considered negligible, since the Er 3+ excitation cross‐section at =488 nm is at least three orders of magnitude smaller than the effective excitation cross‐section () of ultra‐small noble metal nanoclusters and the incident photon flux used for the measurement ( ph s −1 cm −2 ) is far below the saturation regime for the cluster mediated excitation (i.e., ) . Due to the lack of a well‐defined SPR band, plasmonic near‐field enhancement can not explain the out‐of‐resonance Er 3+ excitation …”

Superlinear Photoluminescence by Ultrafast Laser Pulses in Dielectric Matrices with Metal Nanoclusters

“…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. Room temperature PL have been observed in Ag, Au and Pt NCs embedded in soda-lime silicate glasses by light synchrotron irradiation 24 , oxyfluoride and fluoroborated glasses by melt-quenching technique 25,26 and in silica matrices by ion-implantation 27–29 . Among diverse techniques used for the fabrication of metal NPs in dielectrics, ion-implantation is very attractive because it allows the possibility of synthesizing metallic NPs embedded in the near-surface region of the substrate, controlling the depth and the concentration of the NPs.…”

Rare-earth fluorescence thermometry of laser-induced plasmon heating in silver nanoparticles arrays

“…The light-red lines are the best fits to the experimental data obtained with the stretched-exponential decay function: ; in both cases the stretching parameter results β = 0.4 ( β = 1 represents a single-exponential decay). An effective relaxation lifetime can be defined as (Γ is the Euler gamma function) 57 , and we get: ms (pump Ar laser off) and ms (pump Ar laser on at 173 mW). For all these reasons, in the present work we preferred to use the Eu 3+ PL intensity as the thermometric parameter to estimate the rise in temperature of the samples upon laser irradiation.…”