Hailong Xiong

Rapid, morphology-controllable synthesis of GdOF:Ln3+ (Ln = Eu, Tb) crystals with multicolor-tunable luminescence properties

In this paper, GdOF crystals with high uniformity, monodispersity and a variety of well-defined morphologies, such as spheres, nanorods, and nanorod bundles have been successfully synthesized via the urea based homogeneous precipitation method followed by a heat treatment. The influence of pH values, fluoride sources and reaction time on the sizes and morphologies was systematically investigated and discussed. The possible formation mechanism for the precursor has been presented. Under ultraviolet excitation, the GdOF:Ln3+ (Ln = Eu, Tb) submicron spheres show their characteristic f–f emissions and give red, and green emissions, respectively. Moreover, for Tb3+/Eu3+ co-doped GdOF phosphors, tunable emissions have been obtained and the color tones can be tuned from green, through yellow, and then to red by simply adjusting the doping Eu3+ concentrations. This merit of multicolor emissions in the visible region makes these materials hold great promise for applications in field-emission displays.

Facile hydrothermal synthesis and multicolor-tunable luminescence of YPO4:Ln3+ (Ln = Eu, Tb)

Well-crystallized tetragonal YPO4 and YPO4:Ln3+ (Ln = Eu, Tb) nanocrystals with cuboid morphology and narrow size distribution have been successfully synthesized through a facile two-step hydrothermal synthesis route using Y4O(OH)9NO3 as a sacrificial precursor for the first time. The structure, morphology and phase evolution process were significantly affected by the reaction conditions (hydrothermal treatment time and concentration of (NH4)2HPO4). The luminescence colors of YPO4:Tb3+, Eu3+ phosphors can be easily tuned from green to primrose yellow and then to white by adjusting the concentration of Eu3+ ions under 373 nm irradiation. Furthermore, the energy transfer efficiency of YPO4:0.08Tb3+, xEu3+ increased gradually and reached about 94.30% when the concentration of Eu3+ ions was 0.10. The energy transfer mechanism from Tb3+ to Eu3+ has been proved to be a quadrupole–quadrupole interaction mechanism. These merits manifest that the yttrium phosphate phosphors with tunable white light emission may have potential applications in white light-emitting diodes.

Size and morphology-controlled synthesis of vernier yttrium oxyfluoride towards enhanced photoluminescence and white light emission

In this study, a class of vernier yttrium oxyfluoride (Y5O4F7 denoted as V-YOF) with a variety of shapes and sizes was formed by adjusting the crystal growth environment; after calcination, the samples can maintain the morphology of the precursor; this may be attributed to the topotactic chemical transformation. A comparison of the fluorescence results shows that the hexagonally shaped microcrystal strips can effectively improve the light-emitting characteristics; further, to explore the growth mechanism of precursors, time-dependent experiments and three-dimensional growth simulations have been carried out. They suggest that the formation of hexagonal strips may be due to the unique way that the crystals grow from the interior space to the outer wall. Moreover, Tm3+/Dy3+-codoped V-YOF phosphors exhibit excellent white light emission (CIE: x = 0.338, y = 0.313 close to that of standard white light (0.33, 0.33)) due to energy transfer. These results confirm that the V-YOF phosphors may have potential applications in the field of luminescent materials.