Comparative study of the Eu3+ luminescence in the AGd9(SiO4)6O2 (A = Li, Na) red phosphor with high color purity and brightness

Abstract

Novel red-emitting phosphors LiGd9(SiO4)6O2:Eu3+ (LGSO:Eu3+) and NaGd9(SiO4)6O2:Eu3+ (NGSO:Eu3+) were successfully synthesized via a high-temperature solid-state reaction. The phase formation of LGSO:Eu3+ and NGSO:Eu3+ phosphors were characterized by X-ray powder diffraction (XRD). The phosphor could be evidently excited by the near ultraviolet (NUV) light and blue light and then exhibited red light emission, which confirmed by the photoluminescence excitation (PLE) and emission (PL) spectra. According to the photoluminescence spectra, the emission peaks of LGSO:Eu3+ and NGSO:Eu3+ are mainly locate at 595 nm and 615 nm, which attribute to the 5D0 → 7F1 and 5D0 → 7F2 transitions of Eu3+. A comparative study of the optical properties of Eu3+ in the AGd9(SiO4)6O2 (A = Li, Na) red phosphor shows that the optimum concentration of LGSO:Eu3+ phosphors x = 0.20 is less than that of NGSO:Eu3+, x = 0.50, and the emission intensity of the latter is always higher than the former at the same concentration. The ultraviolet–visible spectra indicated that both of hosts tend to absorb energy in the spectral range 200–350 nm, and the band gap of host and phosphor are calculated(LGSO = 3.80 eV, NGSO = 3.99 eV), and the doping of Eu3+ helps to reduce the band gap. The internal quantum efficiency (IQE) of LGSO:0.2Eu3+ and NGSO:0.5Eu3+ were 69.6% and 77.3%, respectively. The chromaticity coordinates of LGSO:0.2Eu3+ and NGSO:0.5Eu3+ were (0.638, 0.360) and (0.643, 0.356), which exhibited high color purity. On this basis, we come to a conclusion that the prepared phosphors enjoy tremendous potentials serve as red emitting phosphor for near ultraviolet white light emitting diodes (NUV WLEDs).