Dependence of the photoluminescence of CdS:In thin films on the excitation power of the laser

Polycrystalline indium doped cadmium sulfide (CdS:In) thin films are prepared by the spray pyrolysis technique on glass substrates at a substrate temperature of 490 °C. The photoluminescence (PL) spectra of the films showed a broad peak in the visible region and another smaller one in the infrared. The first peak is deconvoluted to two Gaussian peaks corresponding to the yellow and red bands, and the second one is deconvoluted to one Gaussian peak corresponding to the infrared band. The influence of the probing laser power on the intensity, position and width at half maximum of these bands is investigated. It is found that the PL intensity of the observed bands increases with laser power until a critical value, after which it slightly decreases then slightly increases again. These variations are interpreted in terms of a band filling mechanism and a laser-induced local heating, where the increase is due to the first effect and the decrease to the second one. A competition between these two effects occurs and the stronger one predominates. The increase before the critical value is explored by plotting the logarithm of the PL integrated intensity against that of the laser power for the three aforementioned bands. Linear fits are performed and the slopes for the three bands are found to be close to 2, which mean that the relation between the PL intensity and laser power is quadratic. Variations in the positions of the peaks and their widths at half maximum with laser power are explained in terms of these two competing effects too.