Novel square plate-like NaGd(WO4)2:Tm3+,Dy3+ phosphors: Synthesis, characterization, tunable luminescence properties and energy transfer behaviors

A series of single-phase color-tunable NaGd(WO4)2(NGW):Tm3+,Dy3+ phosphors were prepared by a facile hydrothermal method. The as-synthesized samples were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), photoluminescence (PL) spectra, and fluorescence decay curves. The results show that all samples are tetragonal scheelite-type pure phase, taking on novel square plate morphology with the side length of 5-6 μm and the central thickness of 2.3 μm. Under the excitation of UV light, NGW:Tm3+ and NGW:Dy3+ exhibit the characteristic emissions of Tm3+ (blue) and Dy3+ (yellow), respectively. White light emission can be achieved by simply adjusting the doping concentration of Tm3+ and Dy3+ in NGW. The luminescence spectra and decay curves reveal the resonance-type energy transfer from Tm3+ to Dy3+ ions and the energy transfer mechanism has been proposed. In addition, the CIE chromaticity coordinates of NGW:Tm3+,Dy3+ can be tuned close to the standard white chromaticity (x = 0.33, y = 0.33). All the results indicate that the obtained products may be potentially applied in the area of UV-excited WLEDs.