Junfeng Yang

Fabrication of CeO 2 nanoparticles decorated three-dimensional flower-like BiOI composites to build p-n heterojunction with highly enhanced visible-light photocatalytic performance

Three-dimensional (3D) flower-like CeO2/BiOI heterostructures with different Ce/Bi molar ratio were successfully synthesized via a hydrothermal method using polyvinylpyrrolidone (PVP) as surfactant. The X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) results indicate that the CeO2 nanoparticles were successfully loaded on the surface of the flower-like BiOI. The photodegradation experiment demonstrated that the photocatalytic efficiency of CeO2/BiOI samples were higher than that of pure BiOI and CeO2, and CeO2/BiOI heterostructure showed the best photocatalytic performance when the amount of CeO2 located at BiOI up to 15%. The result also exhibits that CeO2/BiOI catalysts possess higher photocatalytic efficiency for Rhodamine B (RhB) and methylene orange (MO) degradation, while it has a slight influence for phenol elimination. Meanwhile, the repeated photocatalytic degradation of RhB experiment reveals excellent photostability. A possible mechanism of photocatalysis was also explored and proposed. Furthermore, loading CeO2 on the surface of BiOI can accelerate the separation rate of photogenerated electron-hole pairs, which is analyzed by photoluminescence (PL) spectroscopy, photocurrent experiments (PC) and electrochemical impedance spectroscopy (EIS). These results exhibit that BiOI can be modified by CeO2 and there exists synergistic effect between CeO2 and BiOI. The present work provides a new means to synthesize heterostructured photocatalyst for environmental remediation.

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.

A facile route to the controlled synthesis of β-NaLuF4:Ln3+ (Ln = Eu, Tb, Dy, Sm, Tm, Ho) phosphors and their tunable luminescence properties

Highly uniform and monodisperse β-NaLuF4:Ln3+ (Ln = Eu, Tb, Dy, Sm, Tm, Ho) hexagonal prisms have been synthesized via a facile two-step hydrothermal method without any organic surfactants. The structures, morphologies and luminescence properties of the samples were investigated through XRD, SEM, and PL spectra. Furthermore, the shapes and sizes of the products can be further manipulated through adjusting the pH values of initial solutions. Upon excitation at 368 nm, the β-NaLuF4:Tb3+ phosphors exhibit the strongest green emission at pH = 9.0. Moreover, the photoluminescence properties of β-NaLuF4:Ln3+ were studied in detail, and it was found that the photoluminescence color of the β-NaLuF4:0.03Tm3+ phosphor was close to standard blue light (0.14, 0.08). Under 356 nm irradiation, multicolour emission from blue to sapphire and then to pale green has been achieved from the Tm3+/Dy3+ co-doped β-NaLuF4 samples. The energy transfer process from Tm3+ to Dy3+ was studied and was demonstrated to be an electric dipole–dipole interaction mechanism. It is obvious that the β-NaLuF4 phosphors may have potential applications in the field of full-color displays.