Achieving Eu²⁺ Luminescence at Trivalent Lattice Site in Rb₃Y(PO₄)₂:Eu toward Multicolor Emissions by Carbon and Hydrogen Coreduction

Abstract The advancement of Eu²⁺‐activated luminescent materials tailored to exhibit a range of properties is crucial for addressing the specific demands of various application fields. However, the lack of suitable lattice sites in numerous compounds for stable Eu²⁺ incorporation restricts their potential for diverse optical properties. Herein, a facile strategy of carbon and hydrogen coreduction utilizing graphite crucibles is proposed to effectively achieve the impressive luminescence of Eu²⁺ at trivalent Y sites in Rb₃Y(PO₄)₂:Eu phosphors. Rb₃Y(PO₄)₂:Eu exhibits blue‐violet emission when Eu²⁺ predominantly occupies the Rb1 and Rb2 sites. Inspiringly, by facilitating the reduction of more Eu³⁺ to Eu²⁺, a yellow emission band at 550 nm arising from Eu²⁺ at Y sites emerges, enabling the realization of single‐component white‐emitting and yellow‐emitting Rb₃Y(PO₄)₂:Eu phosphors. The diverse luminescent properties of Rb₃Y(PO₄)₂:Eu expand its potential applications in different white light source devices and optical thermometry. This work presents an innovative synthetic strategy to develop remarkable Eu²⁺ luminescence at trivalent cation sites, thereby broadening the optical properties of the material and enabling multifunctional applications.