An efficient double-perovskite CaLaLiTeO6:Mn4+ far-red phosphor towards indoor plant lighting application

For indoor facility agricultural plant growth lighting the far-red light is an important band, but there is a lack of efficient far-red LED phosphors. In this work, an efficient monoclinic double-perovskite far-red phosphor CaLaLiTeO6: Mn4+ was synthesized. The far-red light emission around 707 nm was realized by 468 nm blue light excitation. The internal quantum efficiency was measured to be 65.24 %. The structural analysis demonstrates that the small radius Ca2+ ions in the double-perovskite structure lead to the increase of [MnO6]8- octahedron distortion and the enhancement of the covalent bonding of Mn-O bonds. The resulting low structural symmetry and strong covalent bonding increase the probability of the d-d transition of Mn4+, enhance the absorption intensity of the blue band in the excitation spectrum, and improve the far-red light emission efficiency. Far-red LED devices were fabricated by coating the synthesized CaLaLiTeO6: 0.6 %Mn4+ phosphors on 465 nm blue diodes. In the laboratory the growth experiments of wheats were carried out by using encapsulated LED devices, which proved that LED can effectively promote the growth of wheat. Our results shed a light on the exploration of efficient far-red phosphors for indoor plant growth lighting application.