Linna Guo

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.

Facile synthesis and optical properties of nitrogen-doped carbon dots

Among the chemical doping elements, nitrogen atoms play a critical role in tuning the intrinsic properties or exploiting new phenomena of carbonaceous materials. Herein, we report a facile strategy to synthesize nitrogen-doped carbon dots (NCDs) using glutamic acid as the precursor via a one-step thermal conversion process. The as-produced NCDs exhibit bright blue photoluminescence (the quantum yield of ca. 23.2%), and the emission wavelength could be slightly tuned through changing the parameters of the synthesizing process. Interestingly, apart from their superior luminescence characters, unexpected cathodoluminescence (CL) and frequency upconverted emission properties were both observed in the NCDs.

Preparation and drug-delivery properties of hollow YVO4:Ln3+ and mesoporous YVO4:Ln3+@nSiO2@mSiO2 (Ln = Eu, Yb, Er, and Ho)

In this paper, size-controlled morphologies of (Y, Gd)VO4 and (Y, Gd)VO4:Ln3+ (Ln = Eu, Yb, Er, and Ho) were obtained via a facile hydrothermal route, and their properties for drug delivery and photoluminescence were investigated. Monodisperse ellipsoid-like hollow (Y, Gd)VO4 were designed by employing (Y, Gd)(OH)CO3 colloidal spheres as a sacrificial template and NH4VO3 as a vanadium source, and the formation mechanism could be interpreted by the Kirkendall effect. The control of particle size for hollow (Y, Gd)VO4 was realized, facilitating their practical application. Mesoporous core-shell structured (Y, Gd)VO4:Ln3+@nSiO2@mSiO2 were designed to improve the properties for drug release. Typically, red emission of YVO4:Eu3+ predominated under 465 nm excitation; the upconversion spectra of YVO4:Yb3+, Er3+ and YVO4:Yb3+, Ho3+ revealed green and red color upon 980 nm excitation, respectively. The biocompatibility and drug release evaluations indicate the potential biological applications of the samples.

Up-conversion luminescence and near-infrared quantum cutting in Y6O5F8:RE3+ (RE = Yb, Er, and Ho) with controllable morphologies by hydrothermal synthesis

Monodisperse and uniform Y(6)O(5)F(8):RE(3+) (RE = Yb, Er, and Ho) microarchitectures with various morphologies have been constructed by a facile surfactant-assisted hydrothermal route, and their up-conversion luminescence and NIR quantum cutting properties were investigated. Hollow hexagonal prisms, microbundle gatherings by rods, and solid hexagonal prisms were designed by employing CTAB, PVP, and EDTA as additives, respectively. Under 980 nm excitation, the Y(5.34)O(5)F(8):0.6Yb(3+), 0.06Er(3+) samples obtained using different additives exhibit similar emission spectra profiles with predominating peaks at 670 nm; the Y(5.34)O(5)F(8):0.6Yb(3+), 0.06Ho(3+) samples give green emissions with the strongest peaks around 544 nm. The NIR quantum cutting for the Y(6)O(5)F(8):Yb(3+), Ho(3+) samples was identified by the NIR emission spectra upon both 360 and 450 nm excitation. The corresponding quantum cutting mechanisms were discussed through the energy level diagrams, in which a back-energy-transfer from Yb(3+) to Ho(3+) was first proposed to interpret the spectral characteristics. A modified calculation equation for the quantum efficiency of Yb(3+)-Ho(3+) coupled by exciting at 450 nm was suggested according to the quantum cutting mechanism. The efficient NIR luminescence and quantum cutting in Yb(3+), Ho(3+) co-doped Y(6)O(5)F(8) reveal a possible application in modifying the solar spectrum to enhance the efficiency of silicon solar cells.

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.

A Study on the H2Ti3O7 Sheet-Like Products During the Formation Process of Titanate Nanotubes

The H2Ti3O7 sheet-like products were successfully obtained during the formation process of titanate nanotubes via alkali hydrothermal synthesis. The morphological features and structural characteristics of the sheet-like products were studied systematically. Results indicate that three types of sheet-like structures, including layered structure, multi-layer nanosheets and single-layer nanosheet of titanate H2Ti3O7, were observed. The structural characteristics of these sheet-like products were determined by high-resolution structure analysis. It is found that the top/bottom surface of these sheet-like structures is the (010) plane of H2Ti3O7