Raman spectroscopy of Co-doped wurtzite ZnS nanocrystals

Raman spectra of wurtzite CoxZn1-xS nanocrystals were investigated. Two main broad Raman peaks centered at 259 and 331 cm(-1) were observed for low doping concentration, which are assigned to A(1)(TO) and E-1(LO) phonon modes and had large redshift compared with that for bulk counterpart. It is suggested that such phenomena be attributed to phonon confinement effects, relaxation of the wave-vector selection rule due to doping effects. Besides two broad peaks, Raman spectra of high doping concentration exhibit five additional peaks at 229, 308, 340, 348, and 362 cm(-1), whose relative intensities are enhanced while frequencies keep constant with increasing Co concentration due to the small reduced mass difference. (C) 2009 Elsevier B.V. All rights reserved.