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Photoluminescence as a Probe of the Electrical Charge Dependence of Gold Nanoparticles.

Electro-optical switching can be achieved by changing the optical absorption of metal nanoparticles by adding or removing electrical charge, corresponding to increased, respectively, decreased electron density. In this work a different approach is taken by changing the photoluminescence properties as a function of electrical charge on gold nanoparticles. Whereas larger gold nanoparticles (diameter d = 5 and 10 nm), exhibiting a plasmon resonance peak in the absorption spectrum, were used to measure changes of the optical absorption spectrum upon electrical charging, for smaller gold nanoparticles (d = 2 and 5 nm) electrical charging was observed via changes of the photoluminescence. Increase and decrease in photoluminescence was observed at positive and negative applied potentials, respectively. The relation between changes of optical absorption and photoluminescence for the 5 nm particles by electrical charging provides information on the influence of the charge state on the electronic properties and therefore the optical transition probability. The reported observation that not only the optical absorption, but also the photoluminescence is affected by alteration of the electrical charge onto gold nanoparticles may open a new way towards electro-optical switching and bio-sensing.