Microstructure and photoluminescence of CdS-doped silica films grown by RF magnetron sputtering

Abstract

Silica films containing CdS nanometer-sized particles with semiconductor contents of 1–10% were produced by radio-frequency magnetron sputtering at room temperature with subsequent annealing. The mean diameter of the CdS nanocrystals (NCs) varied between 4 and 6 nm, with narrow size distribution. High-resolution transmission electron microscopy images obtained for low-semiconductor-fraction samples showed quite a homogeneous NC distribution inside the silica matrix, while the high-concentration samples showed an agglomeration of NCs in a columnar structure. The observed photoluminescence (PL) bands were correlated with the semiconductor concentration. Two intense PL bands, one near the band-gap energy and the other in the red, were observed at low temperature for samples with low CdS fraction. The high-energy band was found to be Stokes shifted by some 200 meV with respect to the absorption edge at room temperature. The samples with high CdS fraction only displayed a broad red emission band, which was attributed to interface states.