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 A1(TO) and E1(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.