Energy Transfer and Multicolor Tunable Luminescence Properties of NaGd0.5Tb0.5−xEux(MoO4)2 Phosphors for UV-LED

Abstract

Molybdate based phosphors have efficient absorption in the ultraviolet (UV) region and can be used for UV-pumped light emitting. A series of NaGd0.5Tb0.5−xEux(MoO4)2 (0 ≤ x ≤ 0.5) multicolor tunable phosphors were prepared via a conventional solid-state reaction method. The as-prepared samples were well characterized by x-ray diffraction patterns, Fourier transform infrared spectroscopy, scanning electronic microscope, electron energy-dispersive spectroscopy, UV–vis diffused reflectance, photoluminescent spectra, decay curve and temperature-dependent photoluminescence spectra. The results indicate that the NaGd0.5Tb0.5−xEux(MoO4)2 (0 ≤ x ≤ 0.5) phosphors exhibit a good crystallinity and form a continuous solid solution with scheelite structure. Under UV excitation, NaGd0.5Tb0.5−xEux(MoO4)2 (0 ≤ x ≤ 0.5) phosphors exhibit characteristic emissions of Tb3+ (5D4 → 7FJ, J = 6, 5, 4, 3) and Eu3+ (5D0 → 7FJ, J = 0, 1, 2, 3, 4). The host NaGd(MoO4)2 has excellent energy transfer efficiency for rare earth ions, and the energy transfer from Tb3+ ions to Eu3+ ions is efficient, which can be confirmed by the decay curve. The energy transfer (ET) process between Tb3+ and Eu3+ was demonstrated to a reasonable type via a dipole–dipole interaction with ET efficiency of about nearly 95%. Moreover, the temperature-dependent luminescence properties indicated that the phosphors possessed good thermal stability. Interestingly, the luminescence color of NaGd0.5Tb0.5−xEux(MoO4)2 phosphors can be easily tuned from green to green-yellow, yellow, orange-yellow and ultimately to red by simply adjusting the related concentrations of Tb3+ and Eu3+ under a single wavelength excitation, which might have potential applications in the fields of as multi-color display and illumination.