Defect induced white-light emission from Mn–doped ZnO films and its magnetic properties

Thin films of Zn_1-xMn_xO (where x = 0.01–0.1), a transparent dilute magnetic semiconductor were grown on a glass substrate using cost-effective chemical spray pyrolysis. All films were polycrystalline and most intense XRD peak changed from (0 0 2) at lower x values to (1 0 0) plane for higher doping level. The deposits possessed the fibrous structure up to x = 0.04, a flowered structure for x = 0.05–0.07, and spheroid structure for x = 0.08–0.10, as revealed by SEM. The visible region, optical transmittance systematically changed from 90% to 55%, with increasing dopant concentration. The optical energy band-gap decreased at higher doping levels attributed to the sp–d exchange interactions. The photoluminescence (PL) spectroscopy revealed the presence of various defects which pronounced with increasing Mn%. As a result of multiple defect induced transitions, the PL spectra spanned the entire visible spectrum. Zn_.95Mn_.05O films showed CIE values with x = 0.333 and y = 0.322, perfectly matching to that of pure white light, with a “Colour Temperature” of 5475 K. The magnetic measurements confirm that the higher Mn-doped films displayed room-temperature ferromagnetism while less doped films showed weak ferromagnetic effects at 5 K.