Photoluminescence of CdSe nanocrystals embedded in a SiOx thin film matrix

Room- and low-temperature photoluminescence studies are reported on CdSe na nocrystals embedded in an SiOx thin film matrix. The main spectral feature for all samples and both temperatures is a broad band whose position does n ot change considerably with nanocrystallite size. The band is assigned to r ecombination through defect states, whose energy depends on the nanocrystal lite size in such a way that they counter-balance the similar dependence of the optical band gap on the nanocrystallite size. A noticeable asymmetry o n the low-energy side of this band at low temperatures is attributed to the existence of a variety of surface defect states and/or a large number of v olume defect states in these nanocrystals. There is evidence to suggest tha t the energy band diagram of CdSe nanocrystals in SiOx matrix is considerab ly different from that of SiOx/CdSe multi-quantum wells. (C) 1999 Elsevier Science B.V. All rights reserved.