Temperature-Dependent Emission of Monolayer-Protected Au38 Clusters

Emission spectra are presented for Au-38 clusters in the temperature regime between 4 and 300 K. At room temperature, a broad emission band around 1.35 eV is observed. Upon cooling, fine structure appears that reveals the presence of at least four emission bands. The lowest energy emission band is resonant with the highest occupied molecular orbital-lowest unoccupied molecular orbital energy gap for Au-38 clusters. We propose that the higher emission energy bands result from emission from higher excited states, which competes with nonradiative relaxation. The high oscillator strengths of the transitions allows for competition between radiative and nonradiative decay from the various excited states although nonradiative decay dominates, giving rise to a low quantum yield and a fast decay (<1 ns).