Strong low-temperature anti-Stokes photoluminescence from coupled silicon nanocrystals

We report efficient low-temperature anti-Stokes photoluminescence (upconver ted photoluminescence= UPL) at resonant excitation of coupled silicon nanoc rystals (NCs) in porous silicon (PSi). This photoluminescence is absent in strongly oxidized porous silicon and oxidized silicon nanocrystals. The UPL is a result of resonant excitation of electron-hole (e-h) pairs spatially separated in neighboring crystals with different band-gap. II is generated by the excitation of a second e-h pair in the larger of the two crystals an d Anger ejection of a carrier into the smaller one, with the larger band-ga p. (C) 2001 Elsevier Science B.V. All rights reserved.