Concentration and thermal quenching of SrGdLiTeO₆: Eu³⁺ red-emitting phosphor for white light-emitting diode

A series of SrGd 1- x LiTeO 6 : x Eu 3+ ( 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 P 2 1 / n (14), accommodate Eu 3+ in a highly distorted C 1 site symmetry without inversion center, and facilitate the enhancing of the 5 D 0 → 7 F 2 hypersensitive transition. The excitation spectra, emission spectra and decay curves indicate that the optimum doping concentration of Eu 3+ is x =0.6. The SrGd 0.4 LiTeO 6 :0.6Eu 3+ 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(I 0 '/I-1)-log( x ), in which I 0 '=I 0 / x 0 and I'=I/ x , with x 0 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.