Novel tungstate phosphors with high external quantum efficiency for plant supplement illumination

Abstract This study reports the synthesis of la0.6158mg0.5w0.467o3:mn4+ (LMWO Mn 4+ ) and La 0.65 Li 0.05 Mg 0.5 W 0.5 O 3 :Mn 4+ (LLMWO:Mn 4+ ) phosphors via high‐temperature reactions, with an aim of augmenting far‐red light in indoor plant cultivation systems. The incorporation of Li 2 CO 3 as a flux reduced the sintering temperature from 1588 to 1488 K. Notably, as Li 2 CO 3 increased to 4 wt%, a phase transformation occurred, from LMWO:Mn 4+ to LLMWO:Mn 4+ . This transformation underscores the second role of Li 2 CO 3 as raw material for the LLMWO:Mn 4+ phase in addition to flux. Subsequently, the emission spectrum underwent a red shift, with a strongest peak from 698 to 713 nm. The emission intensity of LLMWO:1.8% Mn 4+ exhibits remarkable enhancements, being 30 times greater than that of LMWO:0.4% Mn 4+ . Furthermore, the external quantum efficiency (EQE) of LLMWO:1.8%Mn 4+ reaches 62.5%, which exceeds most Mn 4+ ‐activated tungstate phosphors reported to date. Intriguingly, an anti‐thermal‐quenching phenomenon was observed in LLMWO:1.8%Mn 4+ at temperatures below 298 K, where the emission intensity at 298 K increased to 124.1% of that at 80 K. Ultimately, phosphor‐converted light emitting diode device was successfully fabricated utilizing the as‐prepared LLMWO:1.8%Mn 4+ phosphor in conjunction with near‐ultraviolet chip. These results demonstrate a significant potential of the Mn 4+ ‐doped tungstate phosphors in this study for applications in plant supplementary illumination.