Plasmon Enhanced Multi-Photon Excited Photoluminescence of Nobel Metal Nanoclusters

In the last decade, metal nanoclusters (ncs) have emerged as a new kind of efficient nano-emitters with an ultra-small size (less than 2 nm), and tunable emission ranging from visible to infrared wavelengths. Multi-Photon Excited Photoluminescence (MPEPL) has also been observed from Au clusters and their impactful application in nanoscale photonic devices has also been pointed out. In this work, we have studied the MPEPL from metal nanoclusters (Au, Ag, and Pt) embedded in Al₂O₃ matrix by ion implantation. The thermal annealing process allows us to obtain a system composed of larger plasmonic metal nanoparticles (nps) surrounded by photoluminescent ultra-small metal ncs. The excitation wavelength used was of 1064 nm, and emissions occur at visible wavelength, ranging from 450 to 800 nm. The second and fourth-order nature of the MPEPL was verified in a power-dependent study below the damage threshold measured for each sample: 58 and 77 GW/cm² for Ag and Au nanocomposites, respectively. Our experiments show that Au and Ag ncs exhibit greater MPEPL than that observed for Pt ncs, which can be explained as a result of a plasmon-mediated optical process of less intensity for Pt nps. These findings provide new opportunities to combine plasmonic nps and photoluminescent ncs inside a robust inorganic matrix to improve their optical properties. Plasmon-enhanced MPEPL from metal ncs may find potential application as ultrasmall fluorophores in multiphoton sensing, and also in the development of solar cells with highly efficient energy conversion modules.