Luminescence of Ce³⁺ in lanthanum silicon oxynitride

The luminescence properties of lanthanum silicon oxynitride (La-Si-O-N) series doped by trivalent Ce ions have been investigated to seek for tunable wavelength-conversion phosphor for white light emitting diode applications. Four compound hosts of LaSiO₂N, La₄Si₂O₇N₂, La₅Si₃O₁₂N, and La₂Si₆O₃N₈ were synthesized and examined in this work. Crystallographic examination for the equal amount of Ce³⁺ substitution indicated that the covalency degree decreased in a sequence LaSiO₂N > La₂Si₆O₃N₈ > La₄Si₂O₇N₂ > La₅Si₃O₁₂N, not simply in correlation to the ratio of N³/O². Excitation and emission spectrum measurements showed the main features of Ce³⁺ luminescence in the series: the centre of gravity of 5d bands depends on crystal-field splitting more strongly than that on covalency of Ce–N bonding; nephelauxetic effect could not be observed clearly for the investigated series; to some extent Stokes shift was dominated by crystal-field splitting rather than Ce–N covalency degree.