Nature 500, 323–326 (2013)

Credit: © NPG 2013

By introducing tin-doped indium oxide nanocrystals into a thin layer of niobium oxide glass, researchers in Spain and the USA have realized a film whose transmission characteristics can be electronically controlled. The film is highly transparent when a voltage of 4 V is applied. However, at a bias voltage of around 2.3 V, the film selectively blocks near-infrared radiation, and at 1.5 V it provides broadband blocking of visible and infrared radiation. This demonstration implies that 'smart windows' coated with the film could in principle selectively and dynamically control the transmission of solar radiation. The transmission properties of the film can be modified during fabrication by controlling the amount of introduced nanocrystals: a higher concentration leads to greater modulation of near-infrared radiation as a result of there being more free carriers in the film. Experiments reveal that the material is stable and that it retains its properties even after being electrically switched more than 2,000 times. Anna Llordés and co-workers say that the findings demonstrate that when the nanocrystals are covalently bonded to glass the linking plays an important role and can yield new forms of amorphous material with useful functionality.