Quanlin Liu

Structure and magnetic properties of Mn-doped ZnO nanoparticles

We report the crystal structure and magnetic properties of the Zn1-xMnxO compounds synthesized by a combustion method. The Zn1-xMnxO compounds with x=0-0.1 crystallize in the wurtzite ZnO structure. The lattice parameters a and c of Zn1-xMnxO increase linearly with the Mn content, indicating that Mn2+ ions substitute for Zn2+ ions. Scanning electron microscopy shows that the average particle radius of Zn0.95Mn0.05O is about 40 nm. From the Curie-Weiss behavior of susceptibility at high temperature, it was found that the Mn-Mn interaction is dominated by antiferromagnetic coupling with effective nearest-neighbor exchange constant J about -32 K and the large negative value of the Curie-Weiss temperature

Tuning of Photoluminescence by Cation Nanosegregation in the (CaMg)x(NaSc)1-xSi2O6 Solid Solution

Controlled photoluminescence tuning is important for the optimization and modification of phosphor materials. Herein we report an isostructural solid solution of (CaMg)x(NaSc)1-xSi2O6 (0 < x < 1) in which cation nanosegregation leads to the presence of two dilute Eu(2+) centers. The distinct nanodomains of isostructural (CaMg)Si2O6 and (NaSc)Si2O6 contain a proportional number of Eu(2+) ions with unique, independent spectroscopic signatures. Density functional theory calculations provided a theoretical understanding of the nanosegregation and indicated that the homogeneous solid solution is energetically unstable. It is shown that nanosegregation allows predictive control of color rendering and therefore provides a new method of phosphor development.

Increased Eu2+ Content and Codoping Mn2+ Induced Tunable Full-Color Emitting Phosphor Ba1.55Ca0.45SiO4:Eu2+,Mn2+

We demonstrated that a new intermediate composition of Ba(1.55)Ca(0.45)SiO4 between the orthosilicates Ca2SiO4 and Ba2SiO4 yields the best phosphor hosts, and interesting luminescence properties can be found from the Eu(2+) singly doped and/or Eu(2+)/Mn(2+) codoped Ba(1.55)Ca(0.45)SiO4 phosphors. The phosphors can be excited by near-ultraviolet (nUV) light at wavelengths ranging from 200 to 450 nm matching well with the nUV light-emitting diode (LED) chips. As a result of fine-tuning the activators of different Eu(2+) content and Eu(2+)/Mn(2+) couples with different ratios, tunable full-color emission under UV light excitation can be realized by combining the blue emission (460 nm) and green emission (520 nm) originating from Eu(2+) with the red emission (595 nm) from Mn(2+) in the Ba(1.55)Ca(0.45)SiO4 host lattice. Energy-transfer efficiency between Eu(2+) and Mn(2+) increases and tunable emission can be obtained with increasing Mn(2+) doping content. These results indicate that the Ba(1.55)Ca(0.45)SiO4:Eu(2+),Mn(2+) phosphor will have potential use in nUV chip pumped white LED devices.

Crystal structure and magnetic properties of SmCo5.85Si0.90 compound

The crystal structure and magnetic properties of SmCo7−xSix (x=0.1–0.9) compounds were studied by means of x-ray powder diffraction and magnetic measurements. Rietveld refinement of x-ray powder diffraction pattern shows that the as-cast compound SmCo7−xSix with x=0.9 crystallizes in the TbCu7-type structure with the space group P6/mmm, and the doping element Si has a distinct preference to occupy the 3g site. According to the refinement result, the composition of the compound is derived as SmCo5.85Si0.90. The compound SmCo5.85Si0.90 exhibits ferromagnetic order with the Curie temperature of about 717 K and a saturation moment of about 6.58±0.05 μB/f.u. The SmCo5.85Si0.90 compound shows a strong uniaxial magnetocrystalline anisotropy, and an anomalous increase of magnetization at low temperature is observed in an external field applied perpendicular to the easy direction of magnetization.

Passive Films and Corrosion Protection Due to Phosphonic Acid Inhibitors

Abstract For protecting mild steel from corrosion, aminotrimethylidenephosphonic acid (ATMP) was more effective than 1-hydroxyethylidene diphosphonic acid (HEDP), N.N-dimethylidenephosphonoglycine (DMPG), 1-ethyl-phosphonoethylidenediphosphonic acid (EEDP), and ethylenediaminetetramethylidenephosphonic acid (EDTMP). A 20-min treatment in 1.0 mol/L of ATMP with a pH 0.23 at 45°C formed an anti-corrosive complex film that was composed of 48.4% O, 28.6% P, 7.0% Fe, 4.3% N, and 11.7%C, based on x-ray photoelectron spectroscopy and Auger electron spectroscopy. From differences in binding energies of Fe, N, and O, in the shift of C-N and P-O vibration, in the reflection FTIR spectra, and in the change of P-OH and Fe-N vibration before and after film formation, it was deduced that N and O in ATMP were coordinated with Fe2+ in the film.

Structure, Crystallographic Sites, and Tunable Luminescence Properties of Eu2+ and Ce3+/Li+-Activated Ca1.65Sr0.35SiO4 Phosphors

Eu(2+) and Ce(3+)/Li(+) singly doped and Eu(2+)/Ce(3+)/Li(+)-codoped Ca1.65Sr0.35SiO4 phosphors have been synthesized by a solid-state reaction method. The crystal structure was determined by Rietveld refinement to verify the formation of the αL′-Ca2SiO4 phase with the Sr addition into Ca2SiO4, and the preferred crystallographic positions of the Eu(2+) and Ce(3+)/Li(+) ions in Ca1.65Sr0.35SiO4 were analyzed based on a comparison of the unit-cell volumes and the designed chemical compositions of undoped isostructural compounds Ca(2–x)Sr(x)SiO4 (x = 0.25, 0.35, 0.45, 0.55 and 0.65). Ce(3+)/Li(+) singly activated Ca1.65Sr0.35SiO4 phosphors exhibit strong absorption in the range of 250–450 nm and a blue emission peak centered at about 465 nm. When Eu(2+) ions are codoped, the emission colors of Ca1.65Sr0.35SiO4:Ce(3+)/Li(+),Eu(2+) phosphors under the irradiation of 365 nm can be finely tuned from blue to green through the energy transfer from Ce(3+) to Eu(2+). The involved energy-transfer process between Ce(3+) and Eu(2+) and the corresponding mechanism are discussed in detail. The reported Ca1.65Sr0.35SiO4:Ce(3+)/Li(+),Eu(2+) phosphor might be a candidate for color-tunable blue-green components in the fabrication of near-ultraviolet-pumped white-light-emitting diodes (WLEDs).

Blue emission and Raman scattering spectrum from AlN nanocrystalline powders

Photoluminescence and Raman scattering spectra from AIN nanocrystalline powders are studied. A blue emission band centered at 420 nm (2.95 eV) is observed. This band may be ascribed to the transition from the shallow level of V-N to the ground state of the deep level of the V-Al(3-)-3 x O-N(+) defect complexes. A phonon structure resulting fi om the transition from the shallow level to the excited states of the deep level is also observed. The broadening of peaks and the low-wave-number-shift of the phonon frequency observed on the Raman scattering spectra are the result of nano-sized effects

Crystal structure and magnetic properties of SmCo7-xHfx compounds

The crystal structure and magnetic properties of SmCo7-xHfx (x=0.05,0.1,0.2,0.3) compounds were studied by means of x-ray powder diffraction and magnetic measurements. The as-cast compounds SmCo7-xHfx with x=0.1 and 0.2 crystallize in the TbCu7-type structure with the space group P6/mmm. According to the structure refinement, the doping element Hf prefers to occupy the 2e site. The compounds have high Curie temperatures (1080 K for x=0.1, 1075 K for x=0.2), large saturation magnetization (104 emu/g for x=0.1, 102 emu/g for x=0.2 at 5 K), and large magnetic anisotropy fields (244 kOe for x=0.1, 282 kOe for x=0.2 at 5 K) with strong uniaxial magnetocrystalline anisotropy

New boron nitride whiskers: showing strong ultraviolet and visible light luminescence.

Boron nitride whiskers with a special structure have been synthesized by a thermal reaction process. The as-prepared BN whiskers have a length of tens of micrometers and a mean diameter of 500 nm. High-resolution TEM analysis shows that the as-prepared BN whiskers can be described as a nanofiber-interweaved network. Infrared and electron energy loss spectra reveal that the BN whiskers are composed of both sigma-sp2 and sigma-sp3 chemical bonds. The UV-vis absorption spectrum displays the energy band gap of the BN whiskers and multiple fine absorption peaks of the phonon-electron coupling. Both photoluminescence (PL) and cathodoluminescence (CL) measurements show the specially structured BN emits strong UV and visible luminescences, which is a promising material for deep-blue and UV applications.

Effect of Al/Si substitution on the structure and luminescence properties of CaSrSiO4:Ce3+ phosphors: analysis based on the polyhedra distortion

Blue-emitting CaSrSiO4:Ce3+,Li+ phosphors were prepared by a high temperature solid-state method, and the effect of substituting Al3+ for Si4+ in CaSrSiO4:Ce3+,Li+ has been studied. Crystal structures of the as-prepared Ca1−ySr1−ySi1−xAlxO4:yCe3+,yLi+ phosphors were resolved by the Rietveld method, which suggested that all the samples belonged to the orthorhombic symmetry (Pnma) group of α-CaSrSiO4. The photoluminescence (PL) emission and excitation spectra, the lifetime, and the effect of Al3+ concentration on the PL properties were investigated in detail. The emission peaks of the CaSrSi1−xAlxO4:Ce3+,Li+ (x = 0–0.10) phosphors were red-shifted from 452 to 472 nm with increasing Al/Si ratio. The red-shift of the Ce3+ emission is ascribed to the polyhedra distortion of the cations, originating from the variation in the neighboring [(Si,Al)O4] polyhedra, and the detailed mechanism has been discussed.