Optical Properties and Structural Relationships of the Silver Nanoclusters Ag32(SG)19 and Ag15(SG)11

2017 
The recent discovery of stable Ag nanoclusters presents new opportunities to understand the detailed electronic and optical properties of the metal core and the ligands using ultrafast spectroscopy. This paper focuses on Ag32 and Ag15 (with thiolate ligands), which are stable in solution. The steady state absorption spectra of Ag nanoclusters show interesting quantum size effects, expected for this size regime. Using a simple structural model for Ag32, TDDFT calculations show absorption at 480 nm and 680 nm that are in reasonable correspondence with experiments. Ag32(SG)19 and Ag15(SG)11 have quantum yields up to 2 orders of magnitude higher than Au nanoclusters of similar sizes, with an emission maximum at 650 nm, identified as the metal–ligand state. The emission from both Ag nanoclusters has a common lifetime of about 130 ps and a common energy transfer rate of KEET ≥ 9.7 × 109 s–1. A “dark state” competing with the emission process was also observed and was found to be directly related to the differen...
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