Ag Doping Concentration Research Articles

One-Step Preparation and Fluorescence Enhancement Effect in SiO2/Eu2+ Doped with Ag Nanowires

Eu2+ single-doped SiO2 (SiO2/Eu2+) and Eu2+, Ag nanowires co-doped SiO2 (SiO2/Eu2+-Ag) luminescent nanomaterials were prepared by an efficient one-step sol-gel method. Their microstructure and optical properties were characterized, and the fluorescence enhancement of Eu2+ by Ag nanowires was investigated. The experimental results indicate that the average diameter of Ag nanowires doped is 12.5 nm, and the length-diameter ratio is 30. The Ag nanowires cannot only enhance the light absorption of SiO2/Eu2+ in the range of 230-350 nm, but also reduce the fluorescence lifetime of Eu2+. More importantly, the emission intensity is enhanced after doping Ag nanowires, and the red shift phenomenon of the emission spectrum is observed, red shift occurs between 10 and 56 nm. The highest fluorescence intensity is accessed under the Ag doping concentration of 0.10 %. Additionally, the emission of SiO2/Eu2+ with 0.10 % of Ag doping at 456 nm is 16 times stronger than that of pure SiO2/Eu2+. The present results indicate that the fluorescence enhancement is attributed to the local field enhancement and the increased radiative decay rates induced by Ag nanowires.

Controlled synthesis of Li2B4O7:Cu for temperature sensing

With the aim of developing a new phosphor for temperature sensing, the effect of different annealing processes and co-dopants (Ag, In, Dy or Ti) on the TL properties of copper-doped Li2B4O7 synthesized by Solution Combustion Synthesis was investigated. Compared with slow annealing, fast annealing induces a high temperature peak (∼310 °C) in the TL curve of Li2B4O7:Cu. The defect structure of Li2B4O7:Cu synthesized by fast annealing is not reproducible, resulting in high sample-to-sample variability in the TL curves. We tested In, Dy, Ti or Ag as co-dopants in Li2B4O7:Cu and found that Ag co-doping resulted in increased TL intensity and reproducible TL curves from sample to sample. In addition, the relative intensity of the main TL peak at ∼200 °C can be controlled by adjusting the Ag doping concentration. Finally, the effect of light exposure on irradiated samples and the room temperature fading over time have been examined. Li2B4O7:Cu,Ag showed low room light sensitivity and almost no fading over a 24 h storage period in the dark. These features support the application of Li2B4O7:Cu,Ag for temperature sensing.

Effect of Ag doping concentration on the electronic and optical properties of anatase TiO2: a DFT-based theoretical study

The electronic and optical properties of pure and Ag-doped anatase TiO2 have been calculated by spin-polarized density functional theory. Ag-doped TiO2 with different Ag doping concentrations ranging from 2.08 to 8.33 % was investigated, and the electronic and optical properties evaluated. Substitutional Ag doped at Ti sites introduced Ag 4d states just above the valence-band maximum, which may help in shifting visible-light excited electrons to the conduction band. Our results show that increasing the doping concentration will enhance visible-light absorption up to Ag doping concentration of 6.25 %; however, further increase of the doping concentration leads to a decrease in visible-light absorption. These results indicate the possibility of tailoring the band gap and optical absorption of TiO2 doped with Ag by varying the doping concentration. The enhanced visible-light absorption for Ag-doped TiO2 with doping concentration of 6.25 % may be due to the existence of widely distributed Ag 4d states above the valence-band maximum and the optimal doping concentration. Ag doping shifted the absorption edge of TiO2 towards visible light, consistent with recent experimental results. Our calculation results provide a reasonable explanation for the experimental findings.

Theoretic insights into the Ag doping in monolayer and bilayer ZnO armchair nanoribbons: edge effect and position-dependent properties

One-dimensional nanoribbons, thickness of which is smaller than width, exhibit special confinement and edge effects far from uniform in the cross-section. By means of density functional theory, we investigated the influence of the edges and doping positions on the electronic structure of Ag-doped ZnO armchair nanoribbons (ZnOANRs). Ag doping in monolayer and bilayer ZnOANRs (m- and b-ZnOANRs) have all been examined. The results indicated that there is no significant difference on the stability of Ag doping in different positions of both m- and b-ZnOANRs, but exhibits very different electronic properties directly related to the different doping positions. The depth of the acceptor states has essential relationship with the interaction between host O 2p and Ag 4d states in the acceptor. Ag substituting Zn atoms at the inner region of m-ZnOANRs could create shallow acceptors with small hole effective masses, benefit for p-type conduction. Ag doping in the inner region of b-ZnOANRs would create shallow acceptors but larger hole effective masses. The difficulty of hole mobility could be improved by increasing the Ag doping concentration in b-ZnOANRs. The discussion about the mechanism and the suggestion about the achievement in the experiment are interesting and timely.

Fabrication and properties of Bi 2− xAg 3 xS 3 thermoelectric polycrystals

Bi 2− x Ag 3 x S 3 ( x = 0–0.06) polycrystals were fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). The phase, microstructure, electrical and thermal transport properties were investigated with a special emphasis on the influence of Ag doping content. All the Bi 2− x Ag 3 x S 3 powders can be indexed as single phase with an orthorhombic symmetry, a second AgBi 3S 5 phase in SPSed bulks occurs as the doping contents x ≥ 0.02, which enhances the electrical conductivity, resulting in improvement of electrical transport properties for Bi 2− x Ag 3 x S 3 bulk samples. A maximum ZT value reached 0.23 at 573 K for the Bi 1.99Ag 0.03S 3 sample, which is 130% higher than that (0.11) of the pure Bi 2S 3.

Electrical properties and Raman scattering investigation of Ag doped ZnO thin films

Ag-doped ZnO thin films were deposited on quartz glass substrates by a radio-frequency (RF) magnetron sputtering technique at room temperature (RT). The influence of Ag doping content on the electrical and Raman scattering properties of ZnO films were systematically investigated by Hall measurement system and Raman scattering spectrum. Two additional local vibrational modes (LVMs) at 230.0 and 394.5 cm −1 induced by Ag dopant in ZnO:Ag films were observed by Raman analyses at RT, corresponding to Ag atoms located at O sites (LV M Zn−Ag) and Zn sites (LV M Ag−O) in ZnO lattice. Moreover, we further studied the effect of donor Ag O and acceptor Ag Zn defects on the electrical properties of ZnO:Ag films. The results indicate that O-rich condition is preferred to suppress the formation of Ag O defects and enhance Ag Zn defects. The p-type ZnO:Ag film was achieved by properly optimizing the annealing conditions under O-rich condition.

Thermoelectric Properties of Ag-Doped n-Type (Bi2−x Ag x Te3)0.96−(Bi2Se3)0.04 Pseudobinary Alloys

n-Type thermoelectric powders of (Bi2xAgxTe3)0.96(Bi2Se3)0.04 (0 £ x £ 0.05) have been synthesized by mechanical alloying and then consolidated by spark plasma sintering. The analysis results show that the grain size of pure Bi, Te, Ag, and Se powders is decreased to about 1 lm to 0.5 lm after they are mechanically alloyed for 2 h. The power factor of bulk material increases with increasing Ag-doping content, while the trend for the lattice thermal conductivity is the opposite. Bulk (Bi0.99Ag0.04)2(Te0.96Se0.04)3 after milling for 12 h exhibits a higher power factor, lower thermal conductivity, and thus a higher ZT of 0.74 at 373 K.

Effects of Ag doping on the crystallization properties of Sb-rich GeSb thin films

Abstract Ag-doped and un-doped Sb-rich GeSb thin films were deposited by DC magnetron co-sputtering. The electrical, structural, and optical properties of the thin films phase change were investigated using 4-point probe measurement, X-ray diffraction (XRD), transmission electron microscopy (TEM), and a static tester. With increasing Ag doping content, the crystallization temperature and sheet resistance of crystalline state decreased from 325 °C to 283 °C and from 187.33 Ω/□ to 114.62 Ω/□, respectively. XRD patterns of the films showed a Sb hexagonal structure, and the calculated grain size increased from 13.9 nm to 17 nm as the Ag concentration increased. Grain sizes of the Ag-doped thin films were larger than the grain sizes of un-doped thin films, as determined by TEM images. A static tester verified the decreased crystallization speed and optical contrast. Un-doped GeSb crystallization took 160 ns and 16 at.% Ag-doped GeSb crystallization took 200 ns when the laser power was 13 mW. Based on a power–time-effect diagram, the 12.6 at.% Ag-doped GeSb showed good thermal stability in a crystalline state.

Optical and morphological characterization of photocatalytic TiO 2 thin films doped with silver

Silver-doped titanium dioxide thin films were deposited on glass substrates by the sol–gel process. Undoped films and films doped with 1 and 3 mol% Ag were annealed at 100 or 500 °C. The optical and morphological properties of the films were analyzed by optical absorption spectroscopy and scanning electron microscopy. Additionally, the films were evaluated for their ability to degrade methylene blue. It was found that the photocatalytic activity is barely sensitive to silver doping for films annealed at 100 °C, whereas the effect of silver resulted in enhanced photocatalytic activity for films annealed at 500 °C. For the latter annealing temperature, the photocatalytic activity increased with increasing Ag doping concentration.

Influence of Ag-doping on the optical properties of ZnO films

Ag-doped ZnO thin films were prepared on glass substrates by radio frequency co-reactive magnetron sputtering technique. The effects of Ag-doping on the microstructure and optical properties of the ZnO thin films were studied by X-ray diffraction (XRD) and UV–visible spectroscopy. The photoluminescence (PL) measurements at room temperature revealed an ultraviolet and a blue emission. The origin of these emissions was discussed. It was also demonstrated that the optical band edge shifted to a shorter wavelength first as Ag is incorporated, and then to a longer wavelength with the increasing of Ag-doping concentration. The optical band gaps calculated based on the quantum confinement model are in good agreement with the experimental values.

Structural and thermoelectric properties of Ag-doped Bi2(Te0.95 Se0.05)3 thin films prepared by flash evaporation

Ag-doped Bi2(Te0.95Se0.05)3 thermoelectric thin films (Ag: 0–0.5 wt%) with thickness of 800 nm have been deposited on glass substrates by the flash evaporation method at 473 K. The structure and morphology of the thin films were analysed by x-ray diffraction and field emission scanning electron microscopy, respectively. The effects of Ag doping concentration on the thermoelectric properties of the annealed thin films were investigated by room-temperature measurement of the Seebeck coefficient and electrical resistivity. The thermoelectric power factor was enhanced to 16.1 µW cm−1 K−2 at 0.2 wt% Ag doping. The Seebeck coefficients are positive with increasing Ag doping concentration from 0.25 to 0.5 wt%. And the thin films show p-type conduction.

Solid State Reaction Synthesis and Thermoelectric Properties of Ag-Doped Mg<sub>2</sub>Si<sub>0.8</sub>Ge<sub>0.2</sub>

By two-step solid state reaction, Mg2Si0.8Ge0.2 was successfully synthesized .The effect of Ag-doping concentration on the thermoelectric transport properties of p-type Mg2Si0.8Ge0.2 was investigated. With the increasing of Ag-doping concentration, the electrical conductivity σ and Seebeck coefficient α increase correspondingly over the measuring temperature range (300-800K).The peaks of the curves of Seebeck coefficient versus temperature shift towards the lower temperature .When the doping concentration of Ag is 16000ppm(nominal molar percent), the power factor P of Mg2Si0.8Ge0.2 reaches 4.4×10-4W/mK2 at 800K,obviously improved in comparison with the sample with no additive .

Low Resistive Micrometer-Thick SnS : Ag Films for Optoelectronic Applications

Ag-doped films have been grown with a thickness of by thermal evaporation technique on Coring 7059 glass substrates at a substrate temperature of . The effects of doping on the physical properties of the films have been investigated. The physical characteristics of the films are discussed and correlated to the microstructural and electro-optical properties. Electro-optical studies show that undoped films have an electrical resistivity and optical bandgap of and at room temperature. With the increase of Ag dopant concentration, the resistivity of the layers initially decreased, reached a minimum value of at 15 atom % of Ag and again increased thereafter. However, optical bandgap of the films decreased nonlinearly with increase of Ag percentage. An empirical formula , which describes the energy gap as a function of the film composition, has been derived. The doping effect on the surface structure of films was also studied.

Silver-doped lithium manganese oxide thin films prepared by solution deposition

Ag-doped LiMn 2O 4 thin films were prepared by solution deposition using lithium acetate, manganese acetate and silver nitrate as starting materials. The phase identification, surface morphology and electrochemical properties were studied by X-ray diffraction, scanning electron microscopy and galvanostatic charge–discharge experiments. The results show that Ag-doped LiMn 2O 4 film is a composite of LiMn 2O 4 and Ag metal. The films with low Ag content are homogeneous and crack-free. However, some silver agglomeration on the surface of thin films appears as Ag doping content increases. The resistivity of the film decreases with the increase of Ag content, while the specific capacity increases first and then decreases. The film with a higher Ag content has a smaller capacity reduction as the discharge current density increases. The charge–discharge experiments show that the cycling behavior of the films becomes better as Ag content increases.

Synthesis of highly luminescent and photostable ZnS:Ag nanocrystals under microwave irradiation

ZnS:Ag nanocrystals with Ag doping concentrations of 1 at% was synthesized by using 3-mercaptopropionicacid (MPA) as stabilizer. A ZnS shell was formed on surface of the ZnS:Ag nanocrystals by the decomposition of Zn–MPA complex under microwave irradiation. The new ZnS shell passivated the nanocrystal surface and resulted in a significant enhancement of the photoluminescent quantum yield and photostability of the nanocrystals. Under optimum reaction conditions, quantum yield of the ZnS:Ag nanocrystals increased from 2.5 to 10.2% after the shell growth.

Investigation of the variation in weak-link profile of YBa 2Cu 3− xAg xO 7− δ superconductors by Ag doping concentration

The effect of Ag doping concentration on the microstructure, transport properties and weak-link profile of YBa 2Cu 3− x Ag x O 7− δ bulk superconducting compound was investigated through resistance–temperature ( R– T), ac magnetic susceptibility ( χ− T), scanning electron microscope (SEM), X-ray diffraction (XRD) and the critical current density ( J c) versus applied magnetic field ( J c− B) measurements. We used the additive method with cationic ratio of x=0.1−0.4 for the YBCO-Ag system. The change in the silver doping concentration slightly affected the transition temperatures ( T c,zero), whereas, the critical current densities ( J c) of the samples and their magnetic field ( B) dependencies were noticeably affected. The improvement on the microstructural properties of YBCO bulk superconductors was observed in SEM analysis, the J c values increased and their magnetic field dependencies decreased with the increasing of Ag concentration up to x=0.2. As well as the current transport properties. Ag doping up to a certain amount produces texturing that gives rise to a modification in the weak-link profile resulting in an enhanced strength of flux pinning which causes an increase in the current carrying capacity.

Investigation of the variation in weak-link profile of YBa2Cu3$minus;xAgxO7$minus;$delta; superconductors by Ag doping concentration

The effect of Ag doping concentration on the microstructure, transport properties and weak-link profile of YBa2Cu3−xAgxO7−δ bulk superconducting compound was investigated through resistance–temperature (R–T), ac magnetic susceptibility (χ−T), scanning electron microscope (SEM), X-ray diffraction (XRD) and the critical current density (Jc) versus applied magnetic field (Jc−B) measurements. We used the additive method with cationic ratio of x=0.1−0.4 for the YBCO-Ag system. The change in the silver doping concentration slightly affected the transition temperatures (Tc,zero), whereas, the critical current densities (Jc) of the samples and their magnetic field (B) dependencies were noticeably affected. The improvement on the microstructural properties of YBCO bulk superconductors was observed in SEM analysis, the Jc values increased and their magnetic field dependencies decreased with the increasing of Ag concentration up to x=0.2. As well as the current transport properties. Ag doping up to a certain amount produces texturing that gives rise to a modification in the weak-link profile resulting in an enhanced strength of flux pinning which causes an increase in the current carrying capacity.

Abnormal magnetoresistance effect in self-dopedAg2+δTethin films(δ<~0.25)

We report an abnormal room-temperature magnetoresistance behavior in self-doped ${\mathrm{Ag}}_{2+\ensuremath{\delta}}\mathrm{Te}$ films with Ag doping concentration $\ensuremath{\delta}l~0.25.$ Both positive magnetoresistance and negative magnetoresistance are found with the magnetic field applied along perpendicular to the sample surface and opposite direction, respectively. It is also evident from our study that such magnetoresistance (MR) behavior is strongly dependent on the doping concentration \ensuremath{\delta} and the annealing time. The origin of the MR behavior is discussed and tentatively ascribed to the complex structure of the films, which is analyzed by x-ray measurement.