Preparation and Luminescence Properties of Eu³⁺ Doped NASICON-based Red Phosphors

In order to explore a new type of red phosphor, Eu³⁺ doped NASICON structure-based phosphors Na₃Si₂PO₁₂:Eu³⁺ were prepared by high temperature solid phase method in air atmosphere. The crystal structure and optical properties of the samples were systematically studied by X-ray diffraction, diffuse reflectance spectroscopy, fluorescence spectroscopy, fluorescence lifetime decay curve and quantum efficiency. The results demonstrate that XRD patterns confirm the pure phase of Na₃Zr₂Si₂PO₁₂: Eu³⁺ phosphor as obtained, since not any excess peaks can be found in XRD patterns and Eu³⁺ doping does not change the crystal structure of Na₃Zr₂Si₂PO₁₂ host. Eu³⁺ doping ensures the red emission at 618 nm under the excitation at UV light. An optimized doping concentration of Eu³⁺ is 24%, while the quenching mechanism beyond the doping concentration at 24% is electric quadrupole-electric quadrupole interaction according to Rexter Theory. The highest internal and external quantum efficiencies are 61% and 15%, respectively; furthermore, the luminescence quenching can be suppressed even at 150 ℃, depending on a high internal quantum efficiency about 50%. It is packaged into an LED lamp with a color rendering index of 79.4. Therefore, Eu³⁺ doped Na₃Zr₂Si₂PO₁₂ is expected to be used as a new type of red phosphor for white LEDs.