Thermal stability enhancement of an Mn4+-activated germanate phosphor by a cationic non-equivalent substitution strategy†

Mn⁴⁺-activated red-emitting materials have garnered significant attention as a research focus due to their potential in enhancing plant growth. Nonetheless, the creation of thermally stable and high-efficiency red phosphors poses a major challenge, particularly for commercial use. In this research, we utilized a cationic substitution strategy to refine the Mn⁴⁺ doped germanate phosphor. By replacing Mg²⁺ ions with Sc³⁺ ions in the Mg_14−xSc_xGe₅O₂₄:Mn⁴⁺ (MSGO:Mn⁴⁺) phosphor, the emission intensity at room temperature was nearly doubled compared to the non-substituted sample. This enhancement is ascribed to the resonance-enhanced emission effect resulting from lattice distortion. The incorporation of Sc³⁺ ions also led to a marked rise in the internal quantum efficiency, from 65.14% to 91.14%, and an enhancement in the external quantum efficiency from 47.27% to 70.11%. Moreover, Sc³⁺ doping induced negative thermal quenching, as indicated by the sustained increase in the photoluminescence intensity of the Mg_14−xSc_xGe₅O₂₄:Mn⁴⁺ phosphor from 25.1 °C to 225.1 °C, which can be attributed to the introduction of defect energy levels. Ultimately, the optimized Mg_13.75Sc_0.25Ge₅O₂₄:0.01Mn⁴⁺ phosphor was integrated with a blue LED chip to create an LED device, showcasing its application potential in the field of plant lighting.