Highly Efficient Orange-Yellow Emission in (Rb, Cs)₂CaP₂O₇/Eu²⁺ with Robust Thermal Stability

Although white light-emitting diodes (WLEDs) are the main technology in the lighting field, their advancement is limited by the need for luminescent materials with high luminous efficiency and high thermal stability, particularly in the long-wavelength region. To address this issue, in this work, a neighboring-cation substitution engineering approach is proposed and validated. Specifically, by substituting Rb⁺ ions with Cs⁺ ions, distortion of the host crystal structure is successfully induced, which further modulates the local symmetry and crystal field environment of the [CaO₆] octahedron, enabling effective regulation of the Eu²⁺ luminescent center. Moreover, systematic investigations of the crystal structure, morphology, photoluminescence properties, and thermal quenching behavior of the as-prepared phosphors were conducted. The results indicate that both the external quantum efficiency (EQE) and thermal stability of the sample significantly improved after Cs⁺ substitution. Furthermore, by combining the as-synthesized orange-yellow phosphor with commercial blue-emitting BaMgAl₁₀O₁₇/Eu²⁺ (BAM: Eu²⁺) and green-emitting (Ba,Sr)₂SiO₄/Eu²⁺ phosphors, a high-performance WLED device was fabricated. The performance of this device was evaluated to validate its applicability in practical lighting, and the potential of this material for field emission displays (FEDs) was also explored. This work provides a new material system and structural design approach for developing Eu²⁺-activated phosphate-based orange-yellow phosphors with high efficiency and thermal stability.