Xueqiang Liu

Superior removal of arsenic from water with zirconium metal-organic framework UiO-66

In this study, water stable zirconium metal-organic framework (UiO-66) has been synthesized and for the first time applied as an adsorbent to remove aquatic arsenic contamination. The as-synthesized UiO-66 adsorbent functions excellently across a broad pH range of 1 to 10, and achieves a remarkable arsenate uptake capacity of 303 mg/g at the optimal pH, i.e., pH = 2. To the best of our knowledge, this is the highest arsenate As(V) adsorption capacity ever reported, much higher than that of currently available adsorbents (5–280 mg/g, generally less than 100 mg/g). The superior arsenic uptake performance of UiO-66 adsorbent could be attributed to the highly porous crystalline structure containing zirconium oxide clusters, which provides a large contact area and plenty of active sites in unit space. Two binding sites within the adsorbent framework are proposed for arsenic species, i.e., hydroxyl group and benzenedicarboxylate ligand. At equilibrium, seven equivalent arsenic species can be captured by one Zr6 cluster through the formation of Zr-O-As coordination bonds.

Intense short-wavelength photoluminescence from thermal SiO2 films co-implanted with Si and C ions

Intense short-wavelength photoluminescence (PL) observed at room temperature from thermal SiO2 films co-implanted with Si and C is reported. A flat Si profile was first implanted, followed by 1100 °C annealing for 60 min. C ions were subsequently used to be implanted into the same depth region. PL was observed from the as-implanted samples with and without annealing. The PL intensity increases with annealing temperature. Comparing the PL spectra and the PL dynamics of the C-implanted, annealed, Si-implanted (CIASI) SiO2 films with those from Si- and C-implanted SiO2 films suggests that the interaction of Si and C in SiO2 films plays an important role in the luminescence in CIASI SiO2 films.

Energy transfer mechanism in Er3+ doped fluoride glass sensitized by Tm3+ or Ho3+ for 2.7-\mu m emission

Enhanced 2.7 \mu m emission is obtained in Er3+/Tm3+ and Er3+/Ho3+ codoped ZBYA glasses. Absorption and emission spectra are tested to characterize the 2.7 \mu m emission properties of Er3+/Tm3+ and Er3+/Ho3+ doped ZBYA glasses and a reasonable energy transfer mechanism of 2.7 \mu m emission between Er3+ and Tm3+Ho3+) ion is proposed. Codoping of Tm3+ or Ho3+ significantly reduces the lifetime of the Er3+: 4I13/2 level due to the energy transfer of Er3+:4I13/2 ?Tm3+:3F4 or Er3+:4I13/2 ?Ho3+: 5I7. Thus, the 2.7 \mu m emission is strengthened and the 1.5 \mu m emission is decreased accordingly especially in the Er3+/Tm3+ sample. The upconversion effects between the Er3+/Tm3+ and Er3+/Ho3+ doped ZBYA glasses are different attribute to the different energy transfer efficiencies. Both of the two codoped samples possess nearly equal large emission cross section (16.6 \times 10-21 cm-2) around 2.7 \mu m. The results indicate that this Er3+/Tm3+ or Er3+/Ho3+ doped ZBYA glass has potential applications in 2.7 -m laser.

Origin of near to middle infrared luminescence and energy transfer process of Er 3+ /Yb 3+ co-doped fluorotellurite glasses under different excitations

We report the near to middle infrared luminescence and energy transfer process of Er3+/Yb3+ co-doped fluorotellurite glasses under 980, 1550 and 800 nm excitations, respectively. Using a 980 nm laser diode pump, enhanced 1.5 and 2.7 μm emissions from Er3+:I13/2→4I15/2 and I11/2→4I13/2 transitions are observed, in which Yb3+ ions can increase pumping efficiency and be used as energy transfer donors. Meanwhile, Yb3+ can also be used as an acceptor and intensive upconversion luminescence of around 1000 nm is achieved from Er3+:I11/2→4I15/2 and Yb3+: F5/2→4F7/2 transitions using 1550 nm excitation. In addition, the luminescence properties and variation trendency by 800 nm excitation is similar to that using 1550 nm excitation. The optimum Er3+ and Yb3+ ion ratio is 1:1.5 and excess Yb3+ ions decrease energy transfer efficiency under the two pumpings. These results indicate that Er3+/Yb3+ co-doped fluorotellurite glasses are potential middle- infrared laser materials and may be used to increase the efficiency of the silicon solar cells.

Spectroscopic properties and energy transfer parameters of Er3+- doped fluorozirconate and oxyfluoroaluminate glasses

Er3+- doped fluorozirconate (ZrF4-BaF2-YF3-AlF3) and oxyfluoroaluminate glasses are successfully prepared here. These glasses exhibit significant superiority compared with traditional fluorozirconate glass (ZrF4-BaF2-LaF3-AlF3-NaF) because of their higher temperature of glass transition and better resistance to water corrosion. Judd-Ofelt (J-O) intensity parameters are evaluated and used to compute the radiative properties based on the VIS-NIR absorption spectra. Broad emission bands located at 1535 and 2708 nm are observed, and large calculated emission sections are obtained. The intensity of 2708 nm emission closely relates to the phonon energy of host glass. A lower phonon energy leads to a more intensive 2708 nm emission. The energy transfer processes of Er3+ ions are discussed and lifetime of Er3+: 4I13/2 is measured. It is the first time to observe that a longer lifetime of the 4I13/2 level leads to a less intensive 1535 nm emission, because the lifetime is long enough to generate excited state absorption (ESA) and energy transfer (ET) processes. These results indicate that the novel glasses possess better chemical and thermal properties as well as excellent optical properties compared with ZBLAN glass. These Er3+- doped ZBYA and oxyfluoroaluminate glasses have potential applications as laser materials.

2.7 μm emission of high thermally and chemically durable glasses based on AlF3

AlF3-based glasses (AlF3-YF3-CaF2-BaF2-SrF2-MgF2) with enhanced thermal and chemical stability were synthesized and compared with the well-known fluorozirconate glass (ZBLAN). The 2.7 μm mid-infrared emission in the AlF3-based glasses was also investigated through the absorption and emission spectra. Both the temperature of glass transition and the characteristic temperatures (ΔT, Hr, kgl) of the fluoroaluminate glasses were much larger than those of the ZBLAN glasses. The corrosion phenomenon can be observed by naked-eye, and the transmittance dropped dramatically (0% at 3 μm) when the ZBLAN glass was placed into distilled water. However, the AlF3-based glass was relatively stable. The fluoroaluminate glasses possessed large branching ratio (20%) along with the emission cross section (9.4×10−21 cm−2) of the Er3+:4I11/2→4I13/2 transition. Meanwhile, the enhanced 2.7 μm emission in highly Er3+-doped AYF glass was obtained. Therefore, these results showed that this kind of fluoride glass has a promising application for solid state lasers at 3 μm.

Ho 3+ /Er 3+ doped fluoride glass sensitized by Ce 3+ pumped by 1550 nm LD for efficient 2.0 μm laser applications

We present a detailed characterization of enhanced 2.0 μm emission and energy transfer processes by codoping Ce3+ in ZBYA: Ho3+/Er3+ glasses under 1550 nm excitation. The measured absorption and emission spectra show that Er3+ ions are efficiently excited by pumping and energy transfer from Er3+: 4I13/2 to Ho3+: 5I7 level. The 2.0 μm emission from the Ho3+: 5I7→5I8 transition is enhanced by codoping Ce3+ (< 0.5 mol %) ions in the Ho3+/Er3+ doped glasses. However, excess Ce3+ ions in the glass network negatively affect the mid-infrared emission. The upconversion luminescence is dominated by Er3+ (667 nm) red emission in the Ho3+/Er3+ doped sample, which is suppressed after introducing Ce3+ ions. The red emission is abnormally dominated by the Ho3+ (650 nm) emission when the ratio of the three ions (Ho3+/Er3+: Ce3+) is 1:1:0.5. These results indicate that Ce3+ ions can enhance Ho3+: 2.0 μm emission by suppressing the upconversion processes. The Ho3+/Er3+/Ce3+ triply-doped ZBYA glass is a promising material for 2.0 μm fiber laser applications.

Compositional dependence of room-temperature Stark splitting of Yb³⁺ in several popular glass systems.

The room-temperature Stark splitting properties of Yb3+ are practical and valuable for lasers because the working temperature of the gain media intensively increases with the laser output. In this Letter, the room-temperature Stark splitting properties of Yb3+ in several popular laser glasses are contrastively studied. Yb3+-doped germanate (Ge), borate (B), silicate (Si), bismuthate (Bi), tellurite (Te), and fluorophosphate (FP) glasses exhibit large Stark splitting and tend to operate close to the quasi-four-level scheme, whereas phosphate (P) glass shows the weakest Stark splitting and tends to operate close to the quasi-three-level one. Due to the low thermal conductivity of the glass matrix, Yb3+-doped P glass suffers from serious thermal problems and is difficult to achieve high laser output. The Stark splitting is also used to estimate the crystal-field strength of glass hosts and local Yb3+ ligand asymmetry degree. The results show that P glass shows weaker crystal-field effect and lower Yb3+ ligand asymmetry than Ge, Si, and B glasses.

Exchange bias in antiferromagnetic coupled Fe3O4+Cr2O3 nanocomposites

Exchange bias (EB) and magnetic properties of ferrimagnetic (FI) Fe3O4 and antiferromagnetic (AFM) Cr2O3 nanocomposites prepared by mechanical alloying have been investigated. A large EB field of 2.2 kOe at 10 K is observed in one of the nanocomposites, which may be related to the uncompensated and pinned AFM spins at the interface between FI and AFM phases of the nanocomposites. The EB field varies with the strength of cooling field and the content of the Cr2O3 phase, the phenomena observed are explained in terms of interfacial exchange interaction between the two phases.

Exchange bias and phase transformation in α‐Fe2O3+NiO nanocomposites

[Liu, W.] Chinese Acad Sci, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China. Chinese Acad Sci, Int Ctr Mat Phys, Shenyang 110016, Peoples R China. Chinese Acad Sci, Inst Met Res, Shenyang 110016, Peoples R China.;Liu, W (reprint author), Chinese Acad Sci, Shenyang Natl Lab Mat Sci, 72 Wenhua Rd, Shenyang 110016, Peoples R China;wliu@imr.ac.cn