Wenjuan Huang

Different Upconversion Properties of β-NaYF4:Yb3+,Tm3+/Er3+ in Affecting the Near-Infrared-Driven Photocatalytic Activity of High-Reactive TiO2

Double-shell-structured β-NaYF4:Yb(3+),Tm(3+)/Er(3+)@SiO2@TiO2 upconversion photocatalysts have been successfully synthesized by a simple hydrothermal method. It is found that the double-shell-structured photocatalyst consists of uniform β-NaYF4:Yb(3+),Tm(3+)/Er(3+) nanocrystals, SiO2 as the media shell, and anatase TiO2 nanocrystals exposed with the high-reactive {001} facets as the outer shell. The TiO2 shell is modified to absorb both the UV and visible light in order to make sufficient use of the upconverted light from β-NaYF4:Yb(3+),Tm(3+)/Er(3+) for photocatalysis. Effective energy transfer from β-NaYF4:Yb(3+),Tm(3+)/Er(3+) to TiO2 and its importance are confirmed. The photocatalytic activity in the degradation of Rhodamine B (RhB) under the near-infrared (NIR) (980 nm laser) irradiation suggests that the NIR-driven photocatalytic activity of the double-shell-structured photocatalyst is significantly dependent on the properties of the upconversion materials and the irradiated NIR power density. Moreover, the NIR-driven photocatalyst shows stable photocatalytic degradation of RhB in the recycled tests. This study suggests a promising system and a new insight to understand the application of appropriate upconversion materials to effectively utilize the NIR for photocatalytic applications of TiO2-based photocatalysts, which may advance the application of solar energy in the future.

Graphene strongly wrapped TiO2 for high-reactive photocatalyst: A new sight for significant application of graphene

A new idea was employed to simultaneously reduce graphene oxide (GO) and wrap it on the surface of high-reactive anatase TiO2 for fabricating novel TiO2-graphene (GP) hybrid materials. The process was based on the surface negatively charged property of GO. With the introduction of strong chemical interaction between TiO2 and GP, the GP wrapped TiO2 gives a strong red-shift of the light absorption edge and a further narrowed bandgap compared to that of GP randomly supported TiO2. This structure can also significantly enhance the separation efficiency of photogenerated electrons and holes. Furthermore, in contrast to the normal anatase TiO2, as-prepared TiO2 is dominated with the high-reactive {001} facet. The superiority of the formed core-shell structure is confirmed by photocatalytic degradation of methylene blue (MB) under the xenon lamp and visible light irradiation. New photocatalytic mechanisms are also proposed based on the obtained results. This work may open a new doorway for new significant application of GP to prepare more GP-based high-reactive photocatalysts for environmental protection.

Molten salt synthesis of tetragonal LiYF4:Yb3+/Ln3+ (Ln = Er, Tm, Ho) microcrystals with multicolor upconversion luminescence

Well-defined tetragonal LiYF4:Yb3+/Ln3+ (Ln = Er, Tm, Ho) microcrystals were successfully prepared by a surfactant-free molten salt method for the first time. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) spectra were used to characterize the samples. It is found that with prolonged time, the phase of product transforms from orthorhombic YF3 through hexagonal NaYF4 to tetragonal LiYF4, while the morphology changes from nanoparticles via microtubes to micro-sized bi-pyramids. By changing the dopant species (Ln3+), multicolor (yellow, green, and blue) upconversion (UC) emissions can be obtained in LiYF4:Yb3+/Ln3+ under 980 nm laser diode (LD) excitation. The UC mechanisms in co-doped LiYF4 samples were analyzed in detail based on the emission spectra. Importantly, this synthetic methodology may offer a new alternative in the fabrication of high quality rare earth fluorides and open the possibility to meet the increasing commercial demand.

Controlled synthesis of NaYF4 nanoparticles and upconversion properties of NaYF4:Yb, Er (Tm)/FC transparent nanocomposite thin films.

Monodisperse oleic acid stabilized pure NaYF(4) nanoparticles with controlled size and shape have been successfully synthesized by changing the initial reaction temperature. Transparent nanocomposite thin films consisting of NaYF(4):Yb, Er (Tm) upconverting nanoparticles (UCNPs) and fluorocarbon resin (FC) are deposited on the slide glass by dip-coating method. The results show that these nanocomposite thin films exhibit intense green and blue upconversion photoluminescence under 980 nm laser excitation and higher transparency than blank substrate. The NaYF(4):Yb,Er (Tm) nanoparticles and NaYF(4):Yb,Er (Tm)/FC nanocomposite thin films have been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), scanning electron microscopy (SEM), SEM/back-scattered electron (BSE), atomic force microscopy (AFM), UV-Vis spectrophotometer (UVPC), and photoluminescence (PL) spectra. These nanocomposite thin films can be potentially used in solar cells field.

Effect of Heat-treatment Temperature on Upconversion Luminescence of β-NaYF 4 :Yb 3+ ,Er 3+ Nano/Microparticles: Effect of Heat-treatment Temperature on Upconversion Luminescence of β-NaYF 4 :Yb 3+ ,Er 3+ Nano/Microparticles

采用溶剂热法和热分解法分别制备纳/微米的β-NaYF 4 :20%Yb 3+ ,2%Er 3+ 晶体. 根据两种不同粒径颗粒的TG-DTA测试分析, 对其进行不同温度的热处理。通过XRD、SEM、FT-IR以及PL等手段研究不同热处理温度对两种粒径的颗粒的尺寸、形貌以及上转换发光性能的影响. 研究结果表明, 随着热处理温度的升高, 纳/微米颗粒的发光性能主要呈现出先升高后下降的趋势。与未作热处理样品对比发现, 适当的热处理(580℃)可以提高纳米颗粒的发光强度, 却不利于改善微米颗粒发光性能。分析认为, 结晶质量的提高、缺陷浓度的降低以及有机配体的去除, 导致了纳/微米颗粒的发光性能的逐步提高。而过高处理温度(>580℃)引起的相转变(β→α)和表面Na 2 CO 3 的生成又大大降低了稀土离子的发光效率。热处理过程中颗粒之间的不同团聚程度是造成纳/微米颗粒发光性能差异变化的主要原因。

Heat treatment temperature effect on the microstructure and optical properties of Dy2(WO4)3 powders

Dy2(WO4)3 powders were synthesized through liquid-phase reaction. The structure transformation of Dy2(WO4)3 powders were analyzed by differential scanning calorimetry (DSC), X-ray diffractometer (XRD) and Fourier transform infrared spectroscopy (FTIR). The optical absorption and photoluminescence properties were characterized by UV-vis-infra diffuse reflectance spectra and fluorescence spectra. The Dy2(WO4)3 host could absorb deep UV light and transfer the energy of UV light to Dy3+ ions, which convert the high-energy UV light to blue light (482 nm, 4F9/2→6H15/2) and yellow light (547 nm, 4F9/2→6H13/2). The Dy2(WO4)3 powders could also absorb near UV light and exhibit blue and yellow emissions near 482 and 547 nm, respectively. Heat treating promoted the crystallization and regulated the micro-structure of Dy2(WO4)3 hosts. The bands of W-Od anti-symmetric stretching vibration exhibited red shift with the increasing of sintering temperature. The W-Ob-W groups tended to combine with each other to form W-Oc-W groups after heat treating. These regulation of micro-structure had influence on the luminescent color of Dy2(WO4)3. The samples could emit yellow-green, white-yellow and white light under the excitation of 350 nm after being treated at 600, 800 and 1 000 °C, respectively. The prepared Dy2(WO4)3 powders have potential to act as UV absorber for solar cell to improve the conversion efficiency and also exhibit potential for white light LED.