Enhanced Thermal Stability of Red‐Emitting Sr₂Si₅N₈:Eu²⁺ Phosphors from Triggered Applicable Trap Level via Rare Earth Ions Co‐Doping

Abstract To solve the problem of thermal stability of the red‐emitting phosphor Sr₂Si₅N₈:Eu²⁺ with great valuable luminescence performance, trivalent rare earth ions Ln³⁺ (Ln = Dy, Ho, Er, Tm, Nd, and Pr) are co‐doped into Sr₂Si₅N₈: Eu²⁺ lattice to form thermally robust phosphors Sr₂Si₅N₈:Eu²⁺,xLn³⁺(Ln_x‐258, 0 ≤ x ≤ 0.05). The successful incorporation of rare earth ions in the crystal structure and the regulation of luminescent properties are proven by a variety of material characterization techniques and analysis. Although the co‐doping of the selected rare earth ions reduces the luminescence intensity of the phosphor, the Dy_0.01‐258 sample still has a high external quantum efficiency (EQE) of 78.6%. More importantly, the co‐doping of Dy³⁺ with x = 0.01 significantly improves the luminescent thermal stability of phosphors at high temperature and the luminescence intensity of Dy_0.01‐258 samples at 200 °C can be maintained at 94.7% of room temperature. The thermoluminescence spectrum shows that the defects brought about by co‐doping of Dy³⁺ with x = 0.01 introduce trap energy levels, which can compensate for the Eu²⁺ luminescence at high temperature. At the same time, the cathodoluminescence mapping and spectra show that the phosphor has a high saturation current under high‐energy electron bombardment, which indicates that this nitride phosphor also has the potential to be used in field emission display (FEDs). Based on its extraordinary EQE and thermal stability data, this nitride phosphor is the first‐rate among the red phosphors for pc‐wLEDs, and has excellent application prospects in FEDs.