Nitrogen concentration effect on Ce doped SiOxNy emission: towards optimized Ce3+ for DEL applications.
Ce-doped SiO x N y films are deposited by magnetron reactive sputtering from a CeO 2 target under nitrogen reactive gas atmosphere. Visible photoluminescence measurements regarding the nitrogen gas flow reveal a large emission band centered at 450 nm for a sample deposited under a 2 sccm flow. A special attention is paid to the origin of such an emission at high nitrogen concentration. Different emitting centers are suggested in Ce doped SiO x N y films (e.g. band tails, CeO 2 , Ce clusters, Ce 3+ ions), with different activation scenarios to explain the luminescence. X-ray photoelectron spectroscopy (XPS) reveals the exclusive presence of Ce 3+ ions whatever the nitrogen or Ce concentrations, while transmission electron microscopy (TEM) shows no clusters or silicates upon high temperature annealing. With the help of photoluminescence excitation spectroscopy (PLE), a wide excitation range from 250 nm up to 400 nm is revealed and various excitations of Ce 3+ ions are proposed involving direct or indirect mechanisms. Nitrogen concentration plays an important role on Ce 3+ emission by modifying Ce surroundings, reducing the Si phase volume in SiO x N y and causing a nephelauxetic effect. Taking into account the optimized nitrogen growth parameters, the Ce concentration is analyzed as new parameter. Under UV excitation, a strong emission is visible to the naked eye with high Ce 3+ concentration (6 at. %). No saturation of the photoluminescence intensity is observed, confirming again the lack of Ce cluster or silicate phase formation due do the nitrogen presence.
Publisher URL: http://arxiv.org/abs/1801.08795