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Photoluminescence (PL) spectroscopy and Cathodoluminescence (CL) spectroscopy and imaging have been utilized to resolve red and blue emission bands from silicon nanowires. We have found that the blue emission band comes from local defects in the silicon dioxide shell of the wires while the red band comes from interfaces between the silicon dioxide shell and the crystalline silicon core. Time‐resolved PL spectroscopy of hydrogen‐ and oxygen‐terminated silicon nanowires, indicates that surface chemistry plays an essential role in determining the luminescence properties of the nanowires. We suggest that the PL lifetime should be related to nonradiative relaxation processes that take place at the interface of the silicon core and the clad material of the nanowires. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Time‐resolved photoluminescence spectroscopy has been utilized to reveal excitonic transitions in silicon nanowires and silicon nanocrystals. While previous works on porous silicon and silicon nanocrystals have shown a two‐level splitting, e.g., singlet‐triplet states, our measurements reveal the fine structure of the excitons including three semi‐bright states and a ground dark excitonic state. Surprisingly, for silicon nanowires we have found the slowest semi‐dark exciton to fall above the faster semi‐bright excitonic state as opposed to silicon nanocrystals. The results are analyzed in terms of spin and orbital selection rules showing that the interchange in the level's hierarchy corresponds to a swap between spin‐forbidden and orbitally‐allowed states. We assign this surprising phenomenon to the relationship between the exchange interaction and the direct Coulomb interaction, which is affected by the dimensionality of the exciton. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)