A series of SrGd_1-xLiTeO₆:xEu³⁺ (x=0.1-1) red-emitting phosphors, prepared by high-temperature solid-state reaction at 1100℃, is thoroughly investigated by means of X-ray diffraction, diffuse reflectance spectra, photoluminescence spectra, and electroluminescence spectra. These double-perovskite-type phosphors crystallize into monoclinic systems with space group P2₁/n(14), accommodate Eu³⁺ in a highly distorted C₁ site symmetry without inversion center, and facilitate the enhancing of the ⁵D₀ → ⁷F₂ hypersensitive transition. The excitation spectra, emission spectra and decay curves indicate that the optimum doping concentration of Eu³⁺ is x=0.6. The SrGd_0.4LiTeO₆:0.6Eu³⁺ presents the strongest excitation peak at 395 nm, which is adequate for near-UV light-emitting diode (LED) pumping; meanwhile, it exhibits an intense red emission with chromaticity coordinates of (0.6671, 0.3284), an asymmetry ratio of 7.56, a color purity of 98.6%, and a luminous efficacy of radiation of 249 lm/W. The fluorescence lifetime is 721 μs, from which the internal quantum efficiency is determined to be 89.7% via the Judd-Ofelt analysis. The formula proposed by van Uiter (van Uitert L G 1967 J. Electrochem. Soc. 114 1048), is used to elucidate the energy transfer mechanism. However, the plot of log(I/x)-log(x) produces a confusing index s=4.26, which makes it difficult to distinguish the dipole-dipole interaction from the exchange interaction. After analyzing the reason of error, we present a new plot of log(I₀'/I-1)-log(x), in which I₀'=I₀/x₀ and I'=I/x, with x₀ corresponding to the low doping content without nonradiative energy transfer. This plot gives rise to s=5.25, a more reasonable value for the dipole-dipole interaction. The integrated emission intensity at 423 K is as high as 85.2% of that at ambient temperature. The thermal activation energy is determined to be 0.2941 eV according to the model based on a temperature-dependent pathway through a charge transfer state. The prototypical LED based on it can emit a bright red light beam. In conclusion, the phosphor exhibits favorable luminous efficiency, color purity and thermal stability of luminescence, which promises solid-state lighting and display applications.