Far-red emitting MgAl2O4:Cr3+ ceramic phosphors with luminescence thermal stability for plant lighting LEDs

MgAl2O4:Cr3+ far-red emitting ceramic phosphors were prepared by the solid-state reaction method. The photoluminescence characteristics, especially the luminescence thermal stability, thermal conductivity, and its application in phosphor-converted LEDs were studied. Under 450 nm excitation, the ceramic phosphors exhibited an emission range of 650-750 nm and showed a narrow-band emission peaked at 688 nm. It also shows 708 nm and 718 nm far-red emission, which matches well with the absorption peak of the plant phytochrome PFR. The luminescence thermal stability of MgAl1.99O4:0.01Cr3+ was excellent. The integral intensity of the two emissions peaked at 708 nm and 718 nm at 500 K can maintain 98.27% and 98.24% of the counterparts measured at room temperature, respectively, showing zero thermal quenching behavior up to 500 K. The thermal conductivity of the MgAl1.99O4:0.01Cr3+ ceramic was 10.3 W·m-1·K-1. These results indicate that MgAl2O4:Cr3+ ceramic phosphors can be applied in plant lighting when packaged onto 450 nm blue LED chips.