Near-infrared luminescence from small gold nanocrystals

A novel photoluminescence is reported for small metal nanocrystals in the near-infrared region (1.1-1.6 mu m). Near-infrared photoluminescence spectra were measured at room temperature for 1.1 and 1.7 nm Au nanocrystals using a 1.06 mu m excitation source. This photoluminescence is attributed to sp to sp-like transitions, analogous to intraband transitions in bulk gold; however, the exact mechanism is unknown. A conservative estimate for the quantum yield for the 1.7 nm gold nanocrystals is (4.4 +/- 1.5) x 10(-5) at room temperature, more than 5 orders of magnitude greater than that of bulk gold.