Influence Of Li Doping Research Articles

Influence of Li doping on the morphology and luminescence of Ga2O3 microrods grown by a vapor-solid method

Gallium oxide microrods have been grown by an evaporation-deposition method by using a precursor containing lithium in order to check the influence of such dopant on the morphology and physical properties of the obtained β-Ga2O3 structures. SEM studies show that the morphology is modified with respect to undoped gallium oxide, promoting the growth of micropyramids transversal to the microwire axis. Raman analysis reveals good crystal quality and an additional Raman peak centred at around 270 cm−1, characteristic of these samples and not present in undoped monoclinic gallium oxide. The presence of the Li+ ions also influences the luminescence emission by inducing a red-shift of the characteristic UV-blue defect band of gallium oxide. In addition, an intense sharp peak centred around 717 nm observed both by cathodoluminescence (CL) and photoluminescence (PL) is also attributed to the presence of these ions. The Li related luminescence features have also been investigated by PL excitation (PLE) spectra and by the temperature dependence of the luminescence.

Influence of Li doping on structural, electrical, optical and magnetic properties of Zn0.96Mn0.04O nanocrystals

In this paper, we report on the influence of Li doping on the structural, morphological, electrical, optical and magnetic properties of Zn0.96−xMn0.04LixO (for x = 0.02, 0.03, 0.04) nanocrystals synthesized by a simple low-temperature co-precipitation method. Rietveld refinement of the XRD patterns confirmed single phase Wurtzite type hexagonal structure of the nanoparticles and expansion in the lattice cell volume with increasing content of Li. TEM images reveal formation of hexagon shaped nano-crystals and also show a good agreement with the crystallite size estimated from the XRD analysis. The I–V characteristics show that resistivity of the samples decreases with increasing Li concentration. The UV–Vis-NIR absorption studies show a reduction in optical energy band gap than that reported for pure ZnO which decreases gradually with increasing Li concentration, showing a qualitative agreement with the I-V characteristic results. Magnetization measurements show clear evidence of weak ferromagnetic ordering at room temperature, which increases with Li content. The observed ferromagnetism seems to show close correlation with the oxygen vacancy defects induced by Li doping.

Influence of Li doping on domain wall motion in Pb(Zr0.52Ti0.48)O3 films

Li-doped PbZr0.52Ti0.48O3 (PZT) films were utilized to study the effect of A-site acceptor dopants on the mobility of ferroelectric domain walls. For chemical solution-deposited PZT films 2 μm in thickness doped with 1–3 mol% Li, the low-field dielectric permittivity remained between 1200 and 1300. With increasing Li concentration, the reversible Rayleigh constants einit increased from 1080 for undoped PZT films to 1240 for the films doped with 3 mol% Li, while the irreversible Rayleigh parameter showed a peak value at 1 mol% Li doping.

Influence of Li doping on the humidity response of maghemite (γ-Fe2O3) nanopowders synthesized at room temperature

Abstract Li doped and undoped γ - Fe 2 O 3 nanopowders have been synthesized at room temperature via simple method by using ethylene diamine as a precipitating agent. The influence of Li doping on the humidity sensing behavior was investigated by varying the doping concentration of Li (0.15, 0.30, 0.45 and 0.75 mol%). The results revealed that the Li doping was advantageous for tuning the response curves in the lower humidity region. The optimal content for Li doping was found to be 0.45 mol% for which the sensor showed more linear behavior with its potential for device application in comparison with the other samples.

A Li-doped Co3O4 oxygen evolution catalyst for non-precious metal alkaline anion exchange membrane water electrolysers

Li-doped Co3O4 (LixCo3−xO4, x = 0, 0.07, 0.21, 0.35, 0.49) spinel powders were prepared with a thermal decomposition method and characterized by XRD, SEM, TEM, and XPS. The LixCo3−xO4 samples were formed as tetragonal powders with a simple spinel structure and with particle sizes about 30–40 nm. All LixCo3−xO4 samples exhibited a 50 mV more negative onset potential for oxygen evolution reaction (OER) than Co3O4. The influence of Li-doping is discussed regarding cation distribution, electronic conductivity and oxygen binding energy. Li0.21Co2.79O4 exhibited the highest OER activity amongst the five samples. A single cell, non-precious metal alkaline anion exchange membrane water electrolysers (AAEMWE) with Li0.21Co2.79O4 anode exhibited a current density of 300 mA cm−2 at a voltage 2.2 to 2.05 V at temperatures of 20–45 °C and the stability was examined with a continuous operation for 10 h at 300 mA cm−2 and at 30 °C.

Influence of Li-doping on structural characteristics and photocatalytic activity of ZnO nano-powder formed in a novel solution pyro-hydrolysis route

Different types of Li-doped ZnO (LDZ) (Li=0–10wt.%) powders were prepared by following a novel pyro-hydrolysis route at 450°C, and were thoroughly characterized by means of thermo-gravimetry (TG), differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared (FT-IR), Fourier-transform Raman (FT-Raman) spectroscopy, diffuse reflectance spectroscopy (DRS), ultra-violet visible (UV–Vis) spectroscopy, Brunauer–Emmett–Teller (BET) surface area (SA), and zeta potential (ζ) measurements. Photocatalytic activity of these powders was evaluated by means of methylene blue (MB) degradation experiments conducted under the irradiation of simulated and natural solar light. Characterization results suggest that both pure ZnO and LDZ powders are quite thermally stable up to a temperature of 700°C and possess band gap (BG) energies in the range of 3.16–3.2eV with a direct band to band transition and ζ values of −31.6mV to −56.4mV. The properties exhibited by LDZ powders were found to be quite comparable to those exhibited by p-type semi-conducting LDZ powders. In order to study the kinetics of MB degradation reaction under the irradiation of simulated solar light, the Li (0.2–10wt.%) and Al (0.5wt.%) co-doped ZnO (0.2LADZ to 10LADZ) powders were also synthesized and employed for this purpose. The photocatalytic degradation of MB over LADZ catalysts followed the Langmuir–Hinshelwood (L–H) first order reaction rate relationship. The 10LDZ catalyst exhibited highest photocatalytic activity among various powders investigated in this study.

Influence of Li doping on the optical and magnetic properties of ZnO nanorods synthesized by low temperature hydrothermal method

Well-defined pure Zn1−xLixO (x=0, 0.05 and 0.1) nanorods were hydrothermally synthesized at the low temperature of 90°C. The X-ray diffraction patterns of all three compositions with a single diffraction peak (0002) showed the same wurtzite hexagonal structure due to the similar radius of Zn and Li. The optical and magnetic properties were influenced by the oxygen vacancies induced by Li doping in the ZnO nanorods. The Raman shift spectrum indicated a slight increasement of oxygen vacancies which enhanced the green emission and ferromagnetism by the doping of Li in the ZnO nanorods. Besides, p-type ZnO:Li semiconductor nanorods were obtained by Li doping. The characteristics of the UV photodetector with p-ZnO:Li nanorod/n-Si structure were also measured.

Computer Simulation of Adsorption and Separation of CO 2/CH 4 in Modified COF-102

Covalent organic framework (COF) is a porous material with low density and large BET (Brunauer-Emmett-Teller) surface area. They have great potential in gas adsorption and separation. In this work, the adsorption of pure CO 2 and CO 2/CH 4 mixture on modified COF-102 was simulated by using GCMC (grand canonical Monte Carlo). Metal Li was incorporated into COF-102 through three doping methods, including charge exchange, O −-Li + dipolar interaction and O −-Li + chemical bonding. The influence of Li doping on the adsorption of CO 2 was studied. The results showed that among the three methods, the dipole doping is the best way to improve CO 2 adsorption performance. Further, the ligands of COF-102 were replaced by extended aromatic moieties, such as diphenyl and pyrene. The adsorption capacity of CO 2 and CH 4, and the selectivity of CO 2/CH 4 on the ligand-replaced COF-102 were studied. The capacity of CO 2 and CH 4 on the ligand-replaced COF-102 had obvious changes; hence the selectivity of CO 2/CH 4 can be adjusted accordingly.

Improved luminescent behavior of YVO 4:Eu 3+ ceramic phosphors by Li contents

Crystalline phase and surface morphology of phosphors are important factors to determine luminescent characteristics. Li-doped YVO 4:Eu 3+ ceramic samples were prepared by a solid state reaction method. The Li + concentration was varied from 1 to 3 wt% to improve crystallinity and surface morphology of ceramics. Influence of Li doping on luminescent properties of YVO 4:Eu 3+ ceramics has been investigated. Photoluminescence spectra have been measured at room temperature using a luminescence spectrometer and excitation by a broadband incoherent ultraviolet light source with an excitation wavelength of 325 nm. The emitted radiation was dominated by a red emission peak at 620 nm radiated from the 5D 0 → 7F 2 transition of Eu 3+ ions. As Li + ion content increases from 0 to 2 wt%, the photoluminescence (PL) brightness improved. The brightness of 2 wt% Li-doped YVO 4:Eu 3+ ceramic was increased by a factor of 1.43 in comparison with that of YVO 4:Eu 3+ ceramic. The enhanced luminescence resulted not only from the improved crystallinity but also from the enhanced surface roughness. The luminescent intensity and surface roughness exhibited similar behavior as a function of Li + ion concentration.

Enhancement of the luminescent characteristics of Li-doped CaTiO3 : Pr3+ thin films grown by pulsed laser deposition

The influence of Li doping on the crystallization, surface morphology and luminescent properties of CaTiO3 : Pr3+ films has been investigated. The films were grown on Al2O3 (0 0 0 1) substrates using the pulsed laser deposition method under different oxygen pressures. The substrate temperature was fixed at 700 °C and the range of oxygen pressure was 100–400 mTorr. The crystallinity and surface morphology of the films were investigated using x-ray diffraction and atomic force microscopy, respectively. The emitted radiation at 322 nm excitation was dominated by a red emission peak at 613 nm radiated from the transition of 1D2 → 3H4 of Pr3+ ions. In particular, the incorporation of Li+ ions into the CaTiO3 lattice could induce the increase in the intensity of the photoluminescence. The enhanced luminescence may result not only from the improved crystallinity but also from the reduced internal reflections caused by rougher surfaces. The luminescent intensity and surface roughness exhibited similar behaviour as a function of the oxygen pressure.

Improved Luminescent Behavior of YBO3:Eu3+ Phosphors by Li-Doping

Li-doped YBO3:Eu3+ phosphors were prepared by solid state reaction method. Influence of Li doping on the crystallization, surface morphology and luminescent properties of YBO3:Eu3+ phosphors have been investigated. The synthesized materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), excitation and emission. The emitted radiation was dominated by a red emission peak at 593 nm radiated from the 5D0 → 7F1 transition of Eu3+ ions. As Li+ ion content increases from 0 to 0.1 mol, the photoluminescence brightness improved. The brightness of 0.1 mol Li-doped YBO3:Eu3+ phosphor was increased by a factor of 4.08 in comparison with that of YBO3:Eu3+ phosphor. The enhanced luminescence results not only from the improved crystallinity but also from the enhanced grain size. The luminescent intensity and grain size exhibited similar behavior as a function of Li+ ions concentration.

Optical and surface analysis of lithium incorporated GdVO 4:Eu 3+ phosphor powders

GdVO 4:Eu 3+ and Li-doped GdVO 4:Eu 3+ phosphor powders have been studied as potential red phosphors for application to flat panel display application. GdVO 4:Eu 3+ (the molar ratio of Eu 3+ = 0.03) and corresponding Li-doped (nominal molar ratio of Li + = 0.03) phosphors were synthesized by solid state reaction method. The influence of Li-doping on the crystallization, the surface morphology, chemical states, ion distribution and photoluminescent properties of GdVO 4:Eu 3+ phosphor powders were investigated. This phosphor showed photoluminescent brightness and crystallization increased when Li ions were doped. The relationship between crystalline and photoluminescent properties were also studied, i.e., Li +-doping effectively enhanced not only the crystallization but also the photoluminescent brightness of GdVO 4:Eu 3+ powders. Comparing to GdVO 4:Eu 3+, the photoluminescent brightness of Li-doped GdVO 4:Eu 3+ powder was increased by a factor of 2.3 times.

Structure and electronic properties of Li-doped vanadium oxide nanotubes

The influence of Li-doping on the mixed-valent vanadium oxide nanotubes has been investigated using electron energy loss spectroscopy. In particular, the electron diffraction profiles and the vanadium L excitation edges have been studied. We observe that the structure of the vanadium oxide nanotubes is stable against electron transfer upon Li-doping. Excitations at the vanadium L edges show features which are associated with a reduction of the vanadium valency.

Li doping effect on the luminescent characteristics of YVO 4:Eu 3+ thin films grown by pulsed laser deposition

Influence of Li doping on the crystallization, surface morphology and luminescent properties of YVO 4:Eu 3+ films has been investigated. The films have been grown using pulsed laser deposition method on Al 2O 3 (0 0 0 1) substrates under different oxygen pressures. The substrate temperature was fixed at 600 °C and the range of oxygen pressure was 20.00–46.66 Pa. The crystallinity and surface morphology of the films were investigated using X-ray diffraction (XRD) and atomic force microscope (AFM), respectively. The emitted radiation at 312 nm excitation was dominated by a red emission peak at 620 nm radiated from the transition of 5D 0– 7F 2 of Eu 3+ ions. In particular, the incorporation of Li + ions into YVO 4 lattice could induce the increase of the intensity of the photoluminescence. The enhanced luminescence may be resulted not only from the improved crystallinity, but also from the reduced internal reflections caused by rougher surfaces. The luminescent intensity and surface roughness exhibited similar behavior as a function of oxygen pressure.

Enhanced luminescent characteristics of laser-ablated GdVO 4:Eu 3+ thin films by Li-doping

Li-doping has been used to improve luminescent characteristics of thin films. Influence of Li-doping on the crystallization, surface morphology and luminescent properties of GdVO 4:Eu 3+ films have been investigated. Crystallinity and surface morphology of thin films have been very important factors to determine luminescent characteristics and depended on the deposition conditions. The GdVO 4:Eu 3+ and Li-doped GdVO 4:Eu 3+ thin films have been grown using pulsed laser deposition method on Al 2O 3 (0 0 0 1) substrates at a substrate temperature of 600 °C under an oxygen pressure of 13.33–53.33 Pa. The crystallinity and surface morphology of the films were investigated using X-ray diffraction (XRD) and atomic force microscope (AFM), respectively. A broadband incoherent ultraviolet light source with a dominant excitation wavelength of 310 nm and a luminescence spectrometer have been used to measure photoluminescence spectra at room temperature. The emitted radiation was dominated by the red emission peak at 619 nm radiated from the transition of 5D 0– 7F 2 of Eu 3+ ions. Particularly, the peak intensity of Li-doped GdVO 4 films was increased by a factor of 1.7 in comparison with that of GdVO 4:Eu 3+ films. The enhanced luminescence results not only from the improved crystallinity but also from the reduced internal reflections caused by rougher surfaces. The luminescent intensity and surface roughness exhibited similar behavior as a function of oxygen pressure.

Low-Temperature Crystallization and Highly Enhanced Photoluminescence of Gd2-xYxO3:Eu3+ by Li Doping

The influence of Li doping on the crystallization behavior, morphology, and enhancement in photoemission intensity of Gd2-xYxO3:Eu3+ solid−solution was investigated. To maximize an effect of the Li component which is volatile at elevated temperature, the citrate route was adopted for the synthesis at low temperature (650−850 °C). Firing the metal citrate precursor at 650 °C for 5 h was sufficient for the formation of 100 nm sized, nonaggregated, and spherical Li-doped Gd2-xYxO3:Eu3+ particles, whose photoluminescence (PL) emission intensity is comparable with that of commercial red phosphor Y2O3:Eu3+. Such a temperature is much lower than the typical solid-state reaction or spray pyrolysis temperature (>1400 °C). Additional heat treatment up to 850 °C resulted in well-developed 500 nm sized pseudospherical particles whose PL brightness is close to ∼150% in comparison with that of commercial red phosphor. Li-doped Gd2-xYxO3:Eu3+ appears to be a very promising red phosphor because the particle size and shape can be controlled at low temperature (650−850 °C) by the change of Y or Li contents without significant loss of brightness.