Hongxia Guan

Luminescence properties, energy transfer and multisite luminescence of Bi3+/Sm3+/Eu3+-coactivated Ca20Al26Mg3Si3O68 as a potential phosphor for white-light LEDs

A series of blue-to-red emitting Ca20Al26Mg3Si3O68:Bi3+/Sm3+/Eu3+ phosphors were synthesized via a high temperature solid-state reaction method. The crystal structure, luminescence properties, energy transfer and multisite luminescence were investigated in detail. Under ultraviolet (UV) light excitation of 343 nm, Bi3+-doped Ca20Al26Mg3Si3O68 phosphors exhibit a broad blue emission band from 370 to 600 nm which is derived from the allowed transition 3P1 → 1S0 of Bi3+ ions. The Ca20Al26Mg3Si3O68:Sm3+ samples show orange-reddish emission bands at 561, 598, 649 and 708 nm under the excitation of 401 nm. The red emission of Ca20Al26Mg3Si3O68:Eu3+ samples at 587, 616, 654 and 700 nm were detected under the excitation of 392 nm, due to 5D0 → 7FK (K = 1, 2, 3, and 4) transitions. In addition, two kinds of sites for cations (Ca2+) in the host were considered from the high resolution site-selective spectroscopy of Ca20Al26Mg3Si3O68:Eu3+ at low temperature, which matches with the crystal structure of Ca20Al26Mg3Si3O68. Meanwhile, in the Bi3+, Sm3+ co-doped Ca20Al26Mg3Si3O68 samples, the energy transfer from Bi3+ to Sm3+ can be found from the photoluminescence spectra and the fluorescence decay curves. The emission hue can be tuned from cool white (0.270, 0.267) to white (0.334, 0.293), and finally to warm white light (0.405, 0.317) by suitably varying the ratio of Bi3+/Sm3+, indicating that the developed phosphor may be potentially used as a single-component white-emitting phosphor for UV light-emitting diodes. The phosphors CAMSO:Bi3+,Eu3+ develop excellent red-emission properties, so that the Eu3+ doped samples have potential application in WLED.

White light-emitting, tunable color luminescence, energy transfer and paramagnetic properties of terbium and samarium doped BaGdF5 multifunctional nanomaterials

A series of BaGdF5:x% Tb3+,y% Sm3+ phosphors are synthesized by a hydrothermal method, taking the form of irregular nanospheres with average sizes of about 20 nm. An energy transfer from Tb3+ to Sm3+ is observed in the BaGdF5:Tb3+,Sm3+ system, which is justified by the luminescence spectra. Simultaneously, a resonance-type energy transfer from Tb3+ to Sm3+ is demonstrated to occur via the dipole–dipole interaction, for which the critical distance (RTb–Sm) is calculated to be 13.49 A. Furthermore, based on the rare earth concentrations and excitation wavelengths, multiple (white, orange red, green and green yellow) emissions are obtained by Sm3+ ion co-activated BaGdF5:Tb3+ phosphors, which could make them good candidates to be used as full-color phosphors for nUV-LED. More importantly, the obtained samples also exhibit paramagnetic properties at room temperature and low temperature.

Magnetic-downconversion luminescent bifunctional BaGdF5:Dy3+,Eu3+ nanospheres: energy transfer, multicolor luminescence and paramagnetic properties

A series of Dy3+ or/and Eu3+ doped cubic BaGdF5 phosphors were synthesized for the first time by an L-arginine hydrothermal method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence spectroscopies (PL) and luminescence decay. The results indicate that the as-prepared samples are a pure cubic phase of BaGdF5, taking on irregular nanoparticles with an average size of 20 nm. The as-prepared Dy3+ or Eu3+ single doped samples show strong blue and red emissions, originating from the 4F9/2 → 6H15/2 transition of the Dy3+ ions and the 5D1 → 7FJ (J = 1, 2) and 5D0 → 7FJ (J = 1, 2, 4) transition of the Eu3+ ions. Based on the rare earth concentrations and excitation wavelengths, multiple (white, red, blue and green yellow) emissions are obtained by Eu3+ ion co-activated BaGdF5:Dy3+ phosphors. In addition, the energy migration from Dy3+ to Eu3+ has been reported in detail. Furthermore, the obtained samples also exhibit paramagnetic properties at room temperature and low temperature. It is obvious that Dy3+, Eu3+ co-doped BaGdF5 nanomaterials with tunable multicolor emissions may have potential application in the field of full-color displays.

Lu2O2S:Tb3+, Eu3+ nanorods: luminescence, energy transfer, and multicolour tuneable emission

A series of Tb3+ and Eu3+ singly-doped and co-doped rod-like Lu2O2S phosphors have been synthesized via a facile hydrothermal method followed by a subsequent calcination process. The phosphors, with excellent dispersion and uniform rods, exhibit the characteristic Tb3+ or/and Eu3+ emissions with the strongest peaks located at 544 nm (green) and 626 nm (red), respectively. Moreover, the emission intensities of both Tb3+ and Eu3+ remarkably vary with increasing Eu3+ incorporation, and as a result, bright and tunable color emission can be realized in the single-phase Lu2O2S host by varying the ratio of Eu3+ to Tb3+ ions. In addition, the multicolor luminescence of Tb3+ and Eu3+ co-doped rod-like Lu2O2S phosphors can be readily achieved by changing the excitation wavelengths. The energy transfer from Tb3+ to Eu3+ ions in Lu2O2S was systematically investigated in detail. These results prove that the as-synthesized Lu2O2S nanorods are an excellent host for rare earth luminescence, and the Lu2O2S:Tb3+, Eu3+ nanorods with tunable multicolor luminescence properties may have potential applications in the fields of full-color displays, solid-state light and field emission displays.

Electrospinning fabrication and luminescence properties of Lu2O2S:Eu3+ fibers

Luminescent one-dimensional Lu2O2S:Eu3+ fibers were successfully prepared via an electrospinning method followed by a subsequent two-step calcination process for the first time. Scanning electron microscopy (SEM) showed that the as-obtained samples present a fiber-like morphology with uniform size and the diameters of the fibers changed from microscale to nanoscale with the increase of Eu3+ concentration. The emission spectra indicated that the obtained Lu2O2S:Eu3+ fibers exhibited typical Eu3+ (5D0–7FJ) red emission under ultraviolet excitation and the concentration quenching effects occurred in the fibers composed of 3 mol% Eu3+. The decay kinetics behaviors of the Lu2O2S:Eu3+ fibers were investigated, which showed that the fibers composed of 3 mol% Eu3+ also had the longest lifetime. The spectral characteristics and Eu–O ligand behavior were discussed through Judd–Ofelt parameters such as intensity parameters (Ω2, Ω4), radiative transition probability (ARAD), radiative lifetime (τrad), and branching ratio (β0J). In addition, the energy-dispersive X-ray spectra (EDS), thermogravimetry-differential thermal analysis (TG-DTA) and the formation mechanism were also displayed in order to better understand the work.