Jiansheng Huo

Emission Enhancement and Color Tuning for GdVO4:Ln3+ (Ln = Dy, Eu) by Surface Modification at Single Wavelength Excitation

The surface modification can realize systematically the emission enhancement of GdVO4:Ln3+ (Ln = Dy, Eu) microstructures and multicolor emission at single component. The structure, morphology, composition, and the surface ligands modification of as-prepared samples were studied in detail. It is found that the surface-modified ligands can act as sensitizer to improve the emission of the Eu3+ and Dy3+ ions via the energy transfer besides the VO43--Eu3+/Dy3+ process. More importantly, under a single wavelength excitation, the emission color can be effectively tuned by manipulating the doping ratio of the Eu3+ ions in the internal crystal lattice and the Tb3+ ions in the external surface ligands, simultaneously. And further, multicolor emissions are obtained under single wavelength excitation due to the high overlapping between the VO43- absorption and the π-π* electron transition of the ligands. These findings may open new avenues to design and develop new highly efficient luminescent materials.

Phase-Tunable Synthesis of Monodisperse YPO4:Ln3+ (Ln = Ce, Eu, Tb) Micro/Nanocrystals via Topotactic Transformation Route with Multicolor Luminescence Properties

A novel aqueous-based and phase-selected synthetic strategy toward YPO4:Ln3+ (Ln = Ce, Eu, Tb) micro/nanocrystals was developed by selecting specific precursors whose structure topotactically matches with the target ones. It was found that layered yttrium hydroxide (LYH) induced the formation of hexagonal-phased h-YPO4·0.8H2O with the crystalline relationship of [001]LYH//[0001]h-YPO4·0.8H2O, while the amorphous Y(OH)CO3 favored the formation of tetragonal-phased t-YPO4. We also systematically investigated the influence of Na2CO3/NaH2PO4 feeding ratio on the evolutions of morphology and size of the h-YPO4·0.8H2O sample, and we also obtained a novel mesoporous nanostructure for t-YPO4 single crystalline with closed octahedron shape for the first time. Besides, the multicolor and phase-dependent luminescence properties of the as-obtained h-YPO4·0.8H2O and t-YPO4 micro/nanocrystals were also investigated in detail. Our work may provide some new guidance in synthesis of nanocrystals with target phase structure by rational selection of precursor with topotactic structural matching.

Fast synthesis of β-NaYF4:Ln3+ (Ln = Yb/Er, Yb/Tm) upconversion nanocrystals via a topotactic transformation route

Monodisperse β-NaYF4:Ln3+ (Ln = Yb/Er, Yb/Tm) upconversion nanocrystals have been fast synthesized using layered yttrium hydroxide Y2(OH)5NO3·nH2O (LYH) via a topotactic transformation route bypassing the α-NaYF4 intermediate phase. It was found that the topotactic structural matching of [001]LYH//[0001]β-NaYF4 facilitated the direct formation of β-NaYF4, wherein the kinetic α-NaYF4 intermediate phase could be avoided at the initial reaction stage. Besides, the morphology could be effectively tuned by manipulating the NaF/Y(NO3)3 feeding ratio. In addition, the upconversion luminescence properties of the as-prepared β-NaYF4:15%Yb3+/2%Er3+ and β-NaYF4:15%Yb3+/1%Tm3+ were also systematically investigated.

Crystal structures, tunable emission and energy transfer of a novel GdAl12O18N:Eu2+,Tb3+ oxynitride phosphor

We have synthesized a series of Eu2+ and Eu2+/Tb3+ activated novel GdAl12O18N oxynitride phosphors by a traditional solid state reaction. The structural and photoluminescence properties related to the crystal of GdAl12O18N:Eu2+/Tb3+ phosphor are investigated. Rietveld structure refinement and photoluminescence properties of the obtained phosphor indicate that the GdAl12O18N host has only one type of Gd site. GdAl12O18N:Eu2+,Tb3+ samples exhibit a blue emission band that peaks at 460 nm and a green line that peaks at 550 nm, originating from the Eu2+ and Tb3+ ions, respectively. This energy transfer from Eu2+ to Tb3+ was confirmed by the decay times of energy donor Eu2+. In addition, the mechanism of energy transfer from Eu2+ to Tb3+ ions is demonstrated to be a dipole–quadrupole mechanism by the Inokuti–Hirayama (I–H) model. All the results indicate that the Eu2+ and Tb3+ activated phosphor may be a good candidate for blue-green components in UV white LEDs.

Facile Synthesis of Lanthanides (Ce, Eu, Tb, Ce/Tb, Yb/Er, Yb/Ho, and Yb/Tm) Doped LnF3 and LnOF Porous Sub‐microspheres with Multicolor Emissions

Monodisperse YF3 and YOF porous sub-microspheres were synthesized by using a novel sacrificing template method with amorphous Y(OH)CO3 ⋅x H2 O as the precursors and the template. It was found that the size and shape were well maintained, and the condensed precursor was transformed into uniform porous structures after fluoridation. By fine-tuning the feed of the fluorine source, the final product could be converted from YF3 to YOF. A possible growth mechanism is proposed for the uniform porous YF3 structure and the porous yolk-shell-like YOF structure. The luminescence properties showed that the as-synthesized YF3 :Ln3+ (Ln=Eu, Tb, Ce, Ce/Tb, Yb/Er, Yb/Ho, and Yb/Tm) products exhibited strong multicolor emissions, which included down-/upconversion and energy-transfer processes. Additionally, YOX (X=Cl and Br) could be obtained if a different halogen source was used during calcination. However, the spheres were almost completely destroyed. Our novel synthetic route can also be extended to other lanthanide fluorides (REF3 , RE=Gd, Lu), which may open a facile way to fabricate novel porous nanostructures.

Syntheses, crystal structures and photoluminescence properties of Ca9Y(PO4)5(SiO4)F1.5O0.25:Ln3+ (Ln3+ = Eu3+/Tb3+/Dy3+/Sm3+) phosphors for near-UV white LEDs

A series of single-doped Ca9Y(PO4)5(SiO4)F1.5O0.25:Ln3+ (Ln3+ = Eu3+/Tb3+/Dy3+/Sm3+) phosphors have been prepared via conventional high-temperature solid–state reaction. The structural refinement, photoluminescence properties, and decay curves were studied in detail. Under near-UV excitation, the Ca9Y(PO4)5(SiO4)F1.5O0.25:Eu3+/Tb3+/Dy3+/Sm3+ phosphors show the characteristic emissions of Eu3+ (5D0–7F2, red), Tb3+ (5D4–7F5, green), Sm3+ (4G5/2–6H7/2, red), and Dy3+ (4F9/2–6H13/2, yellow). The emission intensities of Ca9Y(1−x/z)(PO4)5(SiO4)F1.5O0.25:xEu3+/zSm3+ are maximized when x = 0.16 and z = 0.10, and the concentration quenching mechanisms are both dominated by dipole–dipole interactions. The excitation spectra of the Ca9Y(PO4)5(SiO4)F1.5O0.25:Eu3+/Sm3+ phosphors show the strongest absorption at about 400 nm, which matches well with the commercially available near-UV-emitting InGaN-based light emitting-diode (LED) chip. Finally, a red LED was fabricated using the present phosphors (with the composition of Ca9Y(PO4)5(SiO4)F1.5O0.25:Eu3+/Sm3+) and exhibited a red emission with high color purity. All the results indicate that Ca9Y(PO4)5(SiO4)F1.5O0.25:Ln3+ phosphors are promising phosphors for white LEDs.

A novel topotactic transformation route towards monodispersed YOF:Ln3+ (Ln = Eu, Tb, Yb/Er, Yb/Tm) microcrystals with multicolor emissions

Design and synthesis of inorganic micro/nanocrystals with target phase/morphology is a focal theme in nanoscience and nanotechnology. Herein, a novel in situ topotactic transformation synthesis strategy, Y4O(OH)9NO3 → Y(OH)2.02F0.98 → YOF towards YOF:Ln3+ (Ln = Eu, Tb, Yb/Er, Yb/Tm) microcrystals has been reported. We have elaborated the in situ topotactic transformation from Y4O(OH)9NO3 to Y(OH)2.02F0.98 based on the topotactic structural matching, where similar anisotropic channel structures along the c-axis and the analogous coordination structure of lanthanide ions were involved. We have also extended this synthesis strategy to the topologically isomorphic Y(OH)3 and β-NaYF4 and found that the fine difference in structural evolution during the transformation processes led to different morphological evolutions for the two. To the best of our knowledge, for the first time, we report such an in situ topotactic transformation with a high degree of crystal lattice rearrangement, where enneagonal channels transformed into hexagonal channels while maintaining the morphology contour. Moreover, we have systematically investigated the influences of experimental variables on the morphology, size, and composition of the final products. Furthermore, the luminescence properties of the as-prepared YOF:Ln3+ microcrystals were emphasized by demonstrating the multicolor emissions via downconversion and upconversion luminescence. Our study may provide significant guidance towards the synthesis of inorganic micro/nanocrystals with a target phase structure/morphology on the basis of topotactic structural matching.