Preparation and optical characteristics of novel oxynitride phases in the R3(Ta/Nb)-O-N system (R = La, Eu, Gd, Ho, Y, Yb)

The synthesis of reactive nitridation precursors prepared by the citrate route has been evidenced with the R3TaO7 and R3NbO7 stoichiometries (R = La, Eu, Gd, Ho, Y, Yb). Novel oxynitride phases have been isolated in the fluorite-type series R3Ta(O,N,□)8 and R3Nb(O,N,□)8where □ represents anionic vacancies. The niobium/tantalum substitution leads to a modification of the absorption properties towards higher wavelengths. The comparison between GdTa, Gd2Ta and Gd3Ta-based oxynitride phases highlights a blue shift of the position of the absorption edge with increasing Gd/Ta ratio. Unlike with RTa and R2Ta stoichiometries, R3Taoxynitride phases generally show a very narrow formation range in temperatures as well as low absorption in the visible.