Nitridation from core-shell oxides for tunable luminescence of BaSi2O2N2 : Eu2 + LED phosphors

Abstract

Rod-like, uniform, and poorly aggregated BaSi₂O₂N₂ : Eu powders with tunable luminescence for white LEDs have been successfully synthesized by direct gas-reduction nitridation from the core-shell oxide (Ba,Eu)CO₃@SiO₂. Maximization of the contact surface between the reactants and minimization of diffusion distances improved the efficiency of the nitridation. Thus, the desired oxynitride phosphors were obtained at relatively low temperatures (around 1100–1200 °C). Under these conditions, the (Ba,Eu)CO₃ cores melted into small seeds which decreased the particle size and promoted the oriented growth of BaSi₂O₂N₂ : Eu. The nucleation and subsequent crystal growth in (Ba,Eu)CO₃@SiO₂ were further discussed in the samples with different Ba/Si ratios. By controlling the nitridation process, tunable luminescence was achieved in the range of 490–530 nm. The low sedimentation rate of the phosphors from this route shows additional advantages in the LED packaging.