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

A series of SrGd1_xLiTeO6:xEu(3+)(x = 0.1-1) red-emitting phosphors, prepared by high-temperature solid-state reaction at 1100 degrees C, 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 P2(1)/n(14), accommodate Eu3+ in a highly distorted C-1 site symmetry without inversion center, and facilitate the enhancing of the D-5(0) -> F-7(2) hypersensitive transition. The excitation spectra, emission spectra and decay curves indicate that the optimum doping concentration of Eu3+ is x = 0.6. The SrGd0.4 LiTeO6:0.6Eu(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 mu s, 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'= 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.