  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.
