Luminescence of Ce ³ + in lanthanum silicon oxynitride

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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 LaSiO 2 N, La 4 Si 2 O 7 N 2 , La 5 Si 3 O 12 N, and La 2 Si 6 O 3 N 8 were synthesized and examined in this work. Crystallographic examination for the equal amount of Ce 3 + substitution indicated that the covalency degree decreased in a sequence LaSiO 2 N > La 2 Si 6 O 3 N 8 > La 4 Si 2 O 7 N 2 > La 5 Si 3 O 12 N, not simply in correlation to the ratio of N 3 /O 2 . Excitation and emission spectrum measurements showed the main features of Ce 3 + 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.