Yanzhao Wang

Design, synthesis and characterization of a novel yellow long-persistent phosphor: Ca2BO3Cl:Eu2+,Dy3+

A novel yellow emitting long-persistent phosphor Ca2BO3Cl:Eu2+,Dy3+ is developed. The incorporation of Dy3+ ions, which act as trap centers, largely extends the thermoluminescence characteristics and evidently enhances the persistent luminescence behavior of the phosphor. Both fluorescence and phosphorescence spectra of Ca2BO3Cl:Eu2+,Dy3+ reveal only one asymmetric broad emission band located at 580 nm, ascribed to the 5d–4f transitions of Eu2+ ions in two different sites. With the optimum doping concentration and sufficient excitation with UV light, the afterglow of samples can persist over 48 h above the recognizable intensity level (≥0.32 mcd m−2), a phenomenon that is infrequent and excellent. Furthermore, Ca2BO3Cl possesses an indirect bandgap of about 5.1 eV. Detailed processes and possible mechanism are studied and discussed.

Crystal structure and up- and down-conversion properties of Yb3+, Ho3+ codoped BaGdF5 solid-solution with different morphologies

A series of Yb3+, Ho3+ codoped BaGdF5 with different morphologies (nanoparticles, peanut-like and capsule-like submicrocrystals) and sizes (37–900 nm) are prepared by a facile additive-assisted hydrothermal route. The crystal structure of BaGdF5 solid-solution is firstly established via the materials studio software and retrieved refinement of the powder XRD data. In addition, upconversion and downconversion luminescence properties of Yb3+, Ho3+ codoped BaGdF5 samples are studied, and the energy transfer (Yb3+ → Ho3+) efficiency of the sample with the strongest UC emission is also calculated. The measured field dependence of magnetization of the Yb3+, Ho3+ codoped BaGdF5 nanoparticles shows excellent paramagnetism. The above results show that versatile lanthanide nanoparticles with these properties combined in a single particle are of considerable importance in biomedical luminescence applications. The Raman spectrum of the BaGdF5 host is presented here, and the low phonon energy is mainly respond for the high UC and DC efficiency of the product.

Structure and luminescence properties of the novel multifunctional K2Y(WO4)(PO4):Ln3+ (Ln = Tb, Eu, Yb, Er, Tm and Ho) phosphors

Lanthanide ion (Tb, Eu, Yb, Tm, Er, and Ho) activated multifunctional phosphors K2Y(WO4)(PO4), (KYWP) were prepared via a conventional solid-state reaction. The crystal structure of KYWP as a new host matrix for luminescence was firstly defined to be the orthorhombic system with space group Ibca (73) via Rietveld refinement of the powder X-ray diffraction and the GSAS software. The vacuum ultraviolet (VUV) excited photoluminescence and cathodoluminescence (CL) analysis of individual Tb3+/Eu3+ activated KYWP phosphors exhibit excellent emission properties in their respective regions. Both KYWP:Tb3+ and KYWP:Eu3+ had high quenching concentration under 147 nm excitation attributed to a long Y–Y distance in KYWP structure, whereas they showed very low quenching concentration under low-voltage electron-beam excitation. This phenomenon was ascribed to the different mechanisms between CL and VUV excited luminescence. Under 980 nm laser excitation, yellow, purple, and red up-conversion (UC) emissions had been achieved in Yb3+–Er3+, Yb3+–Tm3+, and Yb3+–Ho3+ co-doped KYWP, respectively. In Yb3+–Tm3+–Ho3+ tridoped KYWP, red emissions emerging from transitions of Tm3+ changed to the transitions of Ho3+. And the possible reason had been elucidated by a cross-relaxation process between Tm3+ and Ho3+. Laser power dependence of the UC emissions and the energy level diagrams were studied to understand the UC and cross-relaxation mechanisms. The obtained results indicated that the multifunctional lanthanide ion doped KYWP exhibited excellent VUV photoluminescence, CL and multicolor UC luminescence properties.

Near-infrared quantum cutting in Ho3+, Yb3+-codoped BaGdF5 nanoparticles via first- and second-order energy transfers.

Infrared quantum cutting involving Yb3+ 950–1,000 nm (2 F5/2 → 2 F7/2) and Ho3+ 1,007 nm (5S2,5F4 → 5I6) as well as 1,180 nm (5I6 → 5I8) emissions is achieved in BaGdF5: Ho3+, Yb3+ nanoparticles which are synthesized by a facile hydrothermal route. The mechanisms through first- and second-order energy transfers were analyzed by the dependence of Yb3+ doping concentration on the visible and infrared emissions, decay lifetime curves of the 5 F5 → 5I8, 5S2/5F4 → 5I8, and 5 F3 → 5I8 of Ho3+, in which a back energy transfer from Yb3+ to Ho3+ is first proposed to interpret the spectral characteristics. A modified calculation equation for quantum efficiency of Yb3+-Ho3+ couple by exciting at 450 nm was presented according to the quantum cutting mechanism. Overall, the excellent luminescence properties of BaGdF5: Ho3+, Yb3+ near-infrared quantum cutting nanoparticles could explore an interesting approach to maximize the performance of solar cells.

WHITE UPCONVERSION LUMINESCENCE FROM (Yb3+/Tm3+/Ho3+) TRIDOPED GdF3 NANORODS AFTER HEAT TREATMENT

A series of Ho3+/Yb3+/Tm3+ tridoped GdF3 nanorods with different dopant concentrations were synthesized by a hydrothermal method. Transmission electron microscope (TEM) images indicate that the length and diameter of the nanorods is about 90 nm and 31 nm, respectively on average. No bright white upconversion light was observed from the samples with different Yb3+, Ho3+ or Tm3+ concentrations. Unexpectedly, the emission color coordinates of the samples after heat treatment move toward the central white region of the chromaticity diagram, and among these samples, the color coordinate (0.349, 0.329) of GdF3:15% Yb3+, 0.1% Ho3+, 0.8% Tm3+ is the most close to the standard white light (0.333, 0.333). This is unlike previous reports in which white light was achieved via tuning dopant concentration or excitation power. The reasons for the above phenomenon are presented by means of FT-IR spectra and the energy level diagram of dopants.