Enhanced Thermal Stability of Red‐Emitting Sr ₂Si ₅N ₈:Eu ²⁺ 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 Sr ₂Si ₅N ₈:Eu ²⁺ with great valuable luminescence performance, trivalent rare earth ions Ln ³⁺ (Ln = Dy, Ho, Er, Tm, Nd, and Pr) are co‐doped into Sr ₂Si ₅N ₈: Eu ²⁺ lattice to form thermally robust phosphors Sr ₂Si ₅N ₈:Eu ²⁺, xLn ³⁺(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 Dy ³⁺ 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 Dy ³⁺ with x = 0.01 introduce trap energy levels, which can compensate for the Eu ²⁺ 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.