Greatly improved photoluminescence properties of the electrodeposited Y2O3:Eu thin film phosphors by the addition of Na and K ions

In this work, Y₂O₃:Eu³⁺ thin film phosphors were prepared by electro-deposition method. The effect of Na⁺ and K⁺ ions on the photoluminescence properties of Y₂O₃:Eu³⁺ thin film phosphor was studied in details. It was found that the addition of Na⁺ and K⁺ ions could improve the photoluminescence intensity by 3 to 4 times. The highly improved photoluminescence intensity may be caused by different factors. The improved crystallinity and the increased optical volume caused by the flux effect of Na⁺ and K⁺ ions could be the major reasons for the enhanced photoluminescence intensity. It was also found that the average lifetime of Y₂O₃:Eu³⁺ thin film phosphors could be adjusted by the molar amount of Na⁺ and K⁺ ions.     

Electrical and optical properties of r.f.-sputtered amorphous V2O5-CaO-MoO3 films

Amorphous films of the V₂O₅-CaO-MoO₃ system are fabricated by r.f.-sputtering and the d.c. conductivity and optical properties are studied. The conductivity of 1200–1400 nm thick amorphous V₂O₅-CaO-MoO₃ films with different film compositions ranges from 4.7 × 10^–4 to 1.1 S cm^–1 at 458 K. The films are n-type semiconducting. The conduction of the films is attributed to adiabatic small polaron hopping and is primarily due to hopping between V⁴⁺ and V⁵⁺ ions. The films are optically transparent in the visible range. The optical band gap energy is evaluated to be between 2.90 and 2.39 eV. The Urbach tail analysis gives the width of localized states between 0.40 and 0.58 eV. A feasibility study reveals the films to be applicable as transparent film thermistors.     

Infra-red spectra of crystalline phases and related glasses in the TeO2-V2O5-Me2O system

The crystal line phases Me₂O·V₂O₅·2TeO₂ (Me=Li, Na, K, Cs, Ag) and their glasses are studied with the aid of infra-red spectroscopy. The radial distribution function (RDF) curves of two glasses, Na₂O·V₂O₅·2TeO₂ and Cs₂O·V₂O₅·2TeO₂, are obtained by an X-ray diffraction study. An attempt is made to identify the main bands in the infra-red spectra of the crystalline compounds and the glasses. The absorption bands in the 970 to 880 cm^–1 range are assigned to the stretching modes of the VO₂ isolated groups. A trend is observed towards a shift of the high-frequency band by the replacement of an alkaline ion with another in the order Ag⁺, Cu⁺, Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, which is explained by their different polarizing ability. With the aid of X-ray diffraction studies it is shown that the basic structure units in the glasses studied are the VO₄ and TeO₄ groups.     

Structure,magnetic, and electrical studies on vanadium phosphate glasses containing different oxides

Glass system with molar composition (60% P₂O₅–30%V₂O₅–10%X) where X is Li₂O, Na₂O, K₂O, and BaO was prepared. The density and molar volume indicate that the density decreases while the molar volume increases with increasing ionic radius of doped oxides. IR studies reveal the coexistence of V⁴⁺ and V⁵⁺ ions (act as glass modifier and glass former, respectively). The observed paramagnetic behavior of samples indicates that V⁴⁺ > V⁵⁺ (the ratio V⁴⁺/V⁴⁺ + V⁵⁺ > 0.52 as obtained from chemical titration analysis). Mott’s model of conduction was applied to discuss DC electrical conduction mechanism. The prepared glass exhibits semiconducting behavior. However, Ba ion is the only ion which did not contribute to the ionic conduction. The conductivity increases with decreasing ionic radius of doped oxides due to high mobility due to their small size. The effect of hopping distance on the electrical conduction and magnetic properties were discussed. An attempt was done to determine the expected temperature of Ba ionic conduction and its ionic activation energy.     

Optical absorption in co-evaporated V2O5-TeO2 thin films

The electron diffraction pattern shows that co-evaporated V₂O₅-TeO₂ thin film samples are amorphous at room temperature and become polycrystalline at temperatures higher than about 513 K. This behaviour is similar to that of amorphous V₂O₅ thin films. The optical absorption edge of amorphous thin films of V₂O₅-TeO₂ is studied in the wavelength range 200 to 900 nm and the FTIR spectra are studied in the wave number range 400 to 4000 cm^–1. The FTIR spectra of amorphous V₂O₅ thin film are found to be similar to those of amorphous V₂O₅-TeO₂ thin films. This suggests that the coordination number of the vanadium ion in V₂O₅-TeO₂ is the same as that in crystalline V₂O₅, and thus the optical absorption edge of amorphous V₂O₅-TeO₂ thin films can be described by direct forbidden transitions.     

Insertion of H, Li, Na and K into thin films prepared from silicotungstic acid—a photoelectron spectroscopy study

Electrochemical insertion by a set of different ions (H⁺, Li⁺, Na⁺ and K⁺) into a tungsten oxide thin film was studied by photoelectron spectroscopy. The tungsten oxide thin film incorporating Si atoms was produced from a silicotungstic acid (SiWA) solution. The insertion compounds were measured by core level photoelectron spectroscopy (W 4f) and the contributions from ions of different oxidation states could be monitored simultaneously. SiWA films having a W⁶⁺/W_tot ratio of 0.7 could be prepared for all cations investigated. At this ratio the W 4f core level electronic structure for H⁺ inserted SiWA films was found to be very similar to that of H⁺ inserted into crystalline monoclinic WO₃ in that both films show the presence of W⁴⁺, W⁵⁺ and W⁶⁺. The measurements on Li⁺ inserted SiWA films indicate an electronic structure very similar to that of the smaller (H⁺) ion. The K⁺ inserted film displays a similar behaviour although the existence of W⁴⁺ was difficult to ascertain. Interestingly, a different behaviour was observed for the Na⁺ inserted compound. In this case, the binding energy shift of the W 4f peak upon reduction is clearly different from that obtained for the other insertion materials.     

Effect of Nb2O5 seed layer on electrical properties of alkaline niobate based ferroelectric thin films

K_0.5Na_0.5NbO₃ and K_0.5Na_0.5Nb_0.995V_0.005O₃ ferroelectric thin films were prepared by a chemical solution deposition method. The Nb₂O₅ seed layer was introduced to investigate the electrical properties of the films. Crystalline structures and microstructures were analyzed by X-ray diffraction and scanning electron microscope at room temperature. The electrical properties were studied both for the films with and without Nb₂O₅ seed layer. It is found that the films' quality was modified by adding the seed layer, and the V-doping also plays an important role in improving the films quality. The ferroelectric and dielectric properties of the films were obviously enhanced by adding the seed layer, especially for the V-doped film. These results may be due to the better crystallization and microstructure of the films.     

Electrochromic performance of mixed V2O5–MoO3 thin films synthesized by pulsed spray pyrolysis technique

Mixed V₂O₅–MoO₃ thin films were deposited onto the glass and fluorine doped tin oxide (FTO) coated glass substrates, at 400 °C by pulsed spray pyrolysis technique (PSPT). Equimolar vanadium chloride (VCl₃) and ammonium molybdate aqueous solutions were mixed together in volume proportions (5–15% molybdenum) and used as a precursor solution for the deposition of mixed V₂O₅–MoO₃ thin films. The structural, morphological, optical and electrochromic properties of the films deposited at different Mo concentrations were studied. With increase in the percentage of Mo the peaks belonging to tetragonal phase of V₂O₅ eventually disappear and the (1 0 1) orthorhombic V₂O₅ phase is observed. Scanning electron microscopy (SEM) shows micro thread like reticulated morphology. The optical band gap energy varied over 2.91–2.85 eV. All the films exhibited cathodic electrochromism in lithium containing electrolyte (0.5 M LiClO₄ + propylene carbonate (PC)). The highest coloration efficiency (CE) for the V₂O₅ film with 15% MoO₃ mixing was found 35.27 cm² C⁻¹.     

Synthesis of V-doped TiO2 films by chemical bath deposition and the effect of post-annealing on their properties

Amorphous composite films, composed of a Ti_1 − xV_xO₂ solid-solution phase and a V₂O₅ phase, were produced by chemical bath deposition and subsequently air-annealed at various temperatures up to 550 °C. The microstructure and chemical composition of the as-prepared and annealed films were investigated by a combinatorial experimental approach using Scanning electron microscopy, X-ray powder diffraction and X-ray photoelectron spectroscopy. Ultraviolet-Visible Spectrometry was applied to determine the optical band gap of the as-prepared and annealed films. It followed that the incorporation of vanadium in the as-deposited films reduces the optical band gap of TiO₂ from about 3.8 eV to 3.2 eV. Annealing of the films up to 350 °C leads to slight increase of band gap, as attributed to a reduction of the defect density in the initially amorphous oxide films due to the gradual development of long-range order and a concurrent reduction of the V⁴⁺-dopant concentration in the Ti_1 − xV_xO₂ solid-solution phase. The films crystallized upon annealing in air at 550 °C, which resulted in drastic changes of the phase constitution, optical absorbance and surface morphology. Due to the lower solubility of V⁴⁺ in crystalline TiO₂, V⁴⁺ segregates out of the crystallizing Ti_1 − xV_xO₂ solid-solution phase, forming crystalline V₂O₅ at the film surface.     

Ion-selective properties of metastable (VO)<Subscript>0.09</Subscript>V<Subscript>0.18</Subscript>Mo<Subscript>0.82</Subscript>O<Subscript>3</Subscript> · 0.54H<Subscript>2</Subscript>O

This paper describes a thin-film solid electrode with an ion-sensitive membrane based on the mixed oxide (VO)_0.09V_0.18Mo_0.82O₃ · 0.54H₂O. The electrode is selective for tetravalent vanadium in the concentration range 3 ≤ pC _V ⁴⁺ ≤ 5 and acidity range 4.5 ≤ pH ≤ 6, with a slope close to the theoretical value. In the range 1 ≤ pH < 5, the electrode responds to changes in hydrogen ion concentration, with a slope of 50 ± 2 mV/pH. Its alkali-metal-ion response shows up in the range 1 ≤ pC _M ⁺ ≤ 4 for pH ≥ 6. We examine the effect of the Li⁺, K⁺, Na⁺, Cs⁺, Rb⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Co²⁺, Ni²⁺, Mn²⁺, Al³⁺, Cr³⁺, and VO₂⁺ ions on the potential of the electrode and determine its selectivity coefficients for these cations.     

Correlation of electrical properties and internal friction in mixed conduction glasses containing ionic and electronic conduction (1) Fe2O3-Na2O-P2O5 glasses

The electrical properties and internal friction in (40–x)Fe₂O₃·xNa₂0.60P₂O₅ glasses were measured. Two or three peak on internal friction were observed in the temperature range of –100 to 300° C at a frequency of about 1 Hz. The peak area of internal friction could be explained quantitatively by the additivity law of diffusion of Na⁺ ion and hopping of electrons which are carriers similar to those of dielectric loss. Activation energy, peak temperature of dielectric loss and internal friction showed almost the same value. Both relaxation phenomena have the same mechanism which is due to the diffusion of Na⁺ion and the hopping of electrons between Fe²⁺ Fe³⁺. The high-temperature peak is assumed to result from the interaction between protons or alkali ions and non-bridging oxygen.     

Oxidation-reduction equilibria of vanadium in CaO-SiO2, CaO-Al2O3-SiO2 and CaO-MgO-SiO2 melts

A series of redox studies of vanadium have been carried out in CaO-SiO₂, CaO-MgO-SiO₂ and CaO-Al₂O₃-SiO₂ melts/slags equilibrated over oxygen partial pressures (pO₂) range 10^–2–10^–9 atm at 1600°C. V₂O₅ level was varied from 1–5 mol%. Three different melt basicities and alumina contents were investigated. Magnesia content was varied between 3.5 and 4.9 wt%. A newly developed analytical technique based upon electron paramagnetic resonance (EPR) spectroscopy was successfully applied to these melts. Two redox equilibria corresponding to V³⁺/V⁴⁺ and V⁴⁺/V⁵⁺ pairs followed the O-type redox reaction over the oxygen partial pressure range investigated. Higher oxidation states of vanadium were stabilized with increasing basicity of slags. Two redox pairs coexisted within oxygen pressure region 10^–4–10^–6 atm. However, redox ratios did not indicate clear trends with increasing V₂O₅ content in CaO-SiO₂-V₂O₅ system. In CaO-SiO₂-Al₂O₃-V₂O₅ slags, a slight increase in redox ratios (V³⁺/V⁴⁺) was obvious when alumina quantity was changed from 3.22 to 5.44% at a basicity ratio 1.3, indicating an increase in slag acidity. CaO-MgO-SiO₂-V₂O₅ slags showed a sharp decrease in redox ratios (V⁴⁺/V⁵⁺) between 10^–2–10^–6 atm with addition of 3.5 wt% MgO, due to increasing free oxygen ions in slags.     

Structural and electrochromic properties of molybdenum doped vanadium pentoxide thin films by sol-gel and hydrothermal synthesis

Molybdenum-doped vanadium pentoxide (Mo-doped V₂O₅) thin films with doping levels of 3-10 mol% were prepared by dip-coating technique from a stable Mo-doped V₂O₅ sol synthesized by sol-gel and hydrothermal reaction. The Mo-doped V₂O₅ films had a layered V₂O₅ matrix structure along c-axis orientation with Mo⁶⁺ as substitutes. Values of the inserted and extracted charge density of 21.4 and 21.3 mC·cm^− 2 and the transmittance variation (ΔT at 640 nm) between anodic (+ 1.0 V) and cathodic (− 1.0 V) colored states of 41% were observed for the films with 5 mol% Mo⁶⁺ doping. Above this dopant concentration, the charge capacity and ΔT decreased. The enhancement of the electrochemical and electrochromic properties of the films is related to changes in the electronic properties of V₂O₅ films due to the creation of energy levels in the band gap of V₂O₅ by the Mo doping, accompanied by the reduction of the forbidden-band width and the increase of the conductivity.     

X-ray Photoelectron Spectra and Electrical Properties of the K4.3V6O16.2 Polyvanadate

The valence state of vanadium atoms in polycrystalline K_4.3V₆O_16.2 is studied by x-ray photoelectron spectroscopy. By decomposing the V 2p _3/2 peak into Gaussian components, the relative amounts of V⁵⁺, V⁴⁺, and V³⁺ ions in the polyvanadate are evaluated before and after Ar⁺ ion milling. The top surface layer of vacuum-sintered K_4.3V₆O_16.2 is shown to be enriched in potassium and oxygen ions. The 288-K dielectric permittivity, carrier mobility, and carrier concentration are determined by complex-impedance measurements.     

Growth of NiWO4 crystals from a Na2W2O7 flux

Well-formed rod crystals of NiWO₄ were grown from a Na₂W₂O₇ flux by a slow cooling method. The solubility of NiWO₄ in Na₂W₂O₇ increased with increasing temperature. At 1100 °C, NiWO₄ was dissolved in Na₂W₂O₇ at a concentration of about 45 mol %. The eutectic temperature was 615± 5 °C. Flux growth was conducted by heating mixtures at 1100 °C for 10 h, followed by cooling to 500 °C at a rate of 5 °C h^–1. The brownish and transparent crystals up to 15 mm in length were grown from the mixtures of about 40 g. The most suitable solute content was 30 mol %. The grown crystals were bounded by the {100}, {010}, {110}, {102}, and {111} faces. In certain instances, the {111} faces disappeared. The EPMA data showed that sodium from the flux used was not contained within the grown crystals. The crystals of NiWO₄ had a d.c. electrical resistivity of about 1 × 10¹¹ cm.     

High density plasma treatment of polyimide substrate to improve structural and electrical properties of Ga-doped ZnO films

We investigated the effects of a high density O₂ plasma treatment on the structural and electrical properties of sputter-deposited GZO films. The GZO films were deposited on polyimide substrate without substrate heating by RF magnetron sputtering from a ZnO target mixed with 5 wt.% Ga₂O₃. Prior to the GZO film growth, we treated a polyimide substrate with highly dense inductively coupled oxygen plasma. The optical transmittance of the GZO film, about 80%, was maintained regardless of the plasma pre-treatment. However, the resistivity of the film was strongly influenced by the plasma pre-treatment. The resistivity of the GZO film decreased from 1.02 × 10^− 2 Ω cm without an O₂ plasma pre-treatment to 1.89 × 10^− 3 Ω cm with an O₂ plasma pre-treatment.     

Electron spin resonance studies of evaporated V2O5 and co-evaporated V2O5/B2O3 thin films

Electron spin resonance studies of evaporated V₂O₅ and co-evaporated V₂O₅/B₂O₃ amorphous thin films have been made. For lower molar contents of B₂O₃, the co-evaporated V₂O₅/B₂O₃ films show poorly resolved hyperfine structure, whereas for higher content of B₂O₃ the hyperfine spectra are well resolved. This behaviour of films is attributed to the increase in the lifetime of a particular V⁴⁺ ion due to Anderson localization of charge, as the degree of disorder increases with increase in the molar content of B₂O₃. The unpaired electron at a given time is localized on a single ⁵¹V nucleus. The low intensity of ESR signal for higher concentration of V₂O₅ in the co-evaporated V₂O₅/B₂O₃ films has been related to the less effective concentration of V⁴⁺ ions due to antiferromagnetic coupling of the V⁴⁺ ions.     

Enhanced red-emitting phosphor Na<Subscript>2</Subscript>Ca<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>8</Subscript>:Eu<Superscript>3+</Superscript> by charge compensation

A series of novel red-emitting Na₂Ca_3???x Si₂O₈:xEu³⁺ phosphors were synthesized by solid state reactions. The phosphors can strongly absorb 395 nm light, and show red emission with a good color purity. The excitation and emission spectra properties of Na₂Ca₃Si₂O₈:Eu³⁺ were characterized. Na₂Ca₃Si₂O₈:Eu³⁺ with self-compensated and alkali metal ions charge compensated approaches (2Ca²⁺→Eu³⁺ + M⁺, M?=?Li⁺, Na⁺, K⁺) have investigated, which found that the red emission of luminescent intensity can be greatly enhanced, and shows superior luminescent property to the commercial Y₂0₃S:Eu³⁺. The present work implies that the efficient charge compensated phosphors are promising candidates as red-emitting phosphor for w-LEDs.     

Ion-selective properties of nanostructured alkali-metal-doped vanadium oxide

We have studied thin-film electrodes based on nanoparticulate vanadium oxide doped with alkalimetal cations. The hydrogen function of the electrodes manifests itself in the pH range 2–5, with a slope of 55, 54, and 54 ± 2 mV/pH for M _x V₂O₅·nH₂O with M = Li, Na, and K, respectively. Their sensitivity range is 10⁻⁴ to 10⁻¹ mol/l. The electrode potential as a function of concentration follows the Nernst equation with a slope of 55, 55, and 57 ± 2 mV/pC for M = Li, Na, and K, respectively. The Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ selectivity coefficients of the electrodes are determined.     

Electrochemical preparation and characterization of three-dimensional nanostructured Sn2S3 semiconductor films with nanorod network

Three-dimensional (3D) nanostructured Sn₂S₃ semiconductor films have been prepared on ITO-coated glass substrates by potentiostatic electrodeposition at −0.80 V (vs. SCE) from a novel plating bath containing K₄P₂O₃ as a complexing agent and Na₂SO₃ as a stabilizing agent and by subsequent annealing. Results showed that the annealing drove the as-deposited Sn₂S₃ films to grow from a granular structure into a nanorod network structure. The nanorods were around 50-100 nm in diameter and 1000 nm in length. The band gap of the annealed film was 1.65 eV and the conductivity was n type. The carrier mobility achieved up to 20.5 cm² V⁻¹ s⁻¹ due to the direct electrical pathways provided by the nanorod network.