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

The occurrence of a very efficient non-resonant energy transfer process forming ultrasmall Au-Ag nanoalloy clusters and Er3+ ions is investigated in silica. The enhancement of the room temperature Er3+ emission efficiency by an order of magnitude is achieved by coupling rare-earth ions to molecule-like (AuxAg1-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, Au-N 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 degrees 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.