Controllable Eu²⁺-Doped Orthophosphate Blue-/Red-Emitting Phosphors: Charge Compensation and Lattice-Strain Control

Cation-substitution-induced controllable luminescence tuning could efficiently optimize and improve the luminescence performances of novel phosphor materials for realizing high-quality lighting. As important members of the orthophosphate family, ABPO₄ (A = alkali metal Li, Na, K, Rb, Cs; B = alkali earth metal Mg, Ca, Sr, Ba) offers an abundant cation lattice environment for rare earth ions. Herein, we successfully prepared a broad-band red-emitting CsMgPO₄:Eu²⁺ phosphor with an emission peak at 628 nm (fwhm = 118 nm). A series of cation-substitution strategies are designed to adjust and enhance its luminescence performances. The corresponding mechanisms are also investigated and proposed reasonably. A charge-compensation strategy of [Eu²⁺-Si⁴⁺] → [Cs⁺-P⁵⁺] could dramatically enhance the quenching concentration from 0.04 to 0.30, which is attributed to the decrease of Eu³⁺. Two cation-substitution strategies of larger Ba²⁺ (Sr²⁺) ions for Mg²⁺ ions could achieve superior emission adjustment of Eu²⁺ ions from the red to blue (yellow) region due to local lattice distortion. Interestingly, a consecutive emission adjustment from the red to blue region by simply changing the annealed temperature is reported for the first time, and the possible emission tuning mechanism is revealed based on a local lattice-strain control. This study could serve as a guide in developing Eu²⁺-activated ABPO₄ phosphors with improving luminescence performance and controllable luminescence adjustment based on charge compensation and lattice-strain control through various cation substitutions.