Photoacoustic Studies of Annealed CdSxSe1-x (x = 0.26) Nanocrystals in a Glass Matrix

Abstract

Photoacoustic (PA) spectroscopy is applied to study an optical absorption of CdSxSe1-x (x=0.26) nanocrystals in a glass matrix annealed at 700°C for different time durations. As the annealing time increases, a shift of the absorption peak (due to the quantum confinement effect) to lower energy is observed in the PA spectra at room temperatures. The observed absorption peak shifts are used to evaluate the average size of CdSxSe1-x nanocrystals in terms of a simple model. The average radius increases from 2.3 to 4.7 nm as the annealing time increases from 0 to 120 min. The PA signal intensities plotted in the semilogarithmic scale vary linearly below the fundamental absorption edges in accordance with the Urbach rule for the optical absorption coefficient. The steepness factor (slope of exponential optical absorption) of the PA spectra increases with increasing annealing time. The change of the electronic states by annealing is explained by considering that the contribution of the surface states decreases with the increase of the nanocrystal size.