Deep-red luminescent materials have kept booming due to the distinct photophysical properties and broad application prospect in plant cultivation. Here, a series of La1-xMg2/3Nb1/3O3-δ:Mn4+ deep-red phosphors with the emission range of 660–730 nm were developed and lanthanum vacancy was introduced into the matrix via decreasing lanthanum content. The defect induced structure variation of the samples were analyzed detailedly and high structural adjustability of this perovskite was confirmed via X ray diffraction and transmission electron microscopy. By creating lanthanum vacancy into the matrix both the emission intensity and thermal stability of the phosphors were greatly improved. The emission intensity of the optimized La0.6Mg2/3Nb1/3O3-δ:Mn4+ at 423 K was improved almost 16 times than the initial sample at 423 K and kept 83.6% of that at 298 K. Furthermore, deep-red LED device was fabricated by coating this deep-red phosphor onto the near ultraviolet chip and applied to the cultivation of purple perilla. The purple perilla with additional deep-red light compensation in the night grew faster than that without light compensation. This modification strategy investigated here opens a new insight to improve the luminescence property of the phosphors for solid state lighting.