In this work we study the optical absorption mechanisms of about 3 nm mean-size silicon nanocrystals (nc-Si) using photocurrent technique. The absorption spectra of nc-Si are composed of several thresholds with the ground and first excited absorption states clearly identified. These results were confronted with numerically calculated electronic states for nc-Si with average size extracted from transmission electron microscopy (TEM) measurements. Comparison between absorption thresholds and emission processes unambiguously confirms these absorption states as nc-Si related. Finally, our results show the great potential of these nanostructures in terms of absorption properties for visible range photodetection and for photovoltaic applications if a good control of absorption thresholds is provided. (c) 2005 Elsevier Ltd. All rights reserved.