Synthesis, optical properties, energy transfer, thermal behavior, and LED package of Eu3+ doped lutetium tungsten oxide phosphors

Abstract By using a solid-state reaction method, Eu3+ doped monoclinic phase of Lu2WO6, mixture of Lu2WO6 and Lu2W3O12, Lu2W3O12, and hexagonal phase of Lu6WO12 lutetium tungsten oxide phosphors were synthesized. The obtained phosphors were composed of micrometre or nanometre scale particles. The energy-dispersive spectra (EDS) illustrated that the W atom percent increased with the sequence of Lu6WO12, Lu2WO6, mixture of Lu2WO6 and Lu2W3O12, and Lu2W3O12. The diffuse reflection (DR) spectra presented the broad absorption bands in the ultraviolet wavelength range and the energy gap values were evaluated based on the DR spectra. The photoluminescence (PL) excitation and emission spectra illustrated that the Lu2WO6 presented the most intense PL intensities in the four phosphors and the optimal Eu3+ concentration was 20 mol% in Lu2WO6 phosphors. The 20 mol% Eu3+ doped Lu2WO6 phosphor presented good thermal stability and kept 85% intensity of 50 °C at 200 °C. The deduced lifetime of Eu3+ 5D0→7F2 transition was several hundred micro-minutes. The energy transfer processes and the energy transfer efficiency were analysed based on the energy level diagram and the PL emission spectra. The obtained red phosphor was packaged into 308 nm chips and red light-emitting diodes (LEDs) were obtained. The chromaticity coordinates and the color purity were measured to evaluate the packaged LED devices. The results suggest that the Eu3+ doped Lu2WO6 has good thermal stability and has potential applications in phosphor converted LEDs.