The synthesis and afterglow luminescence properties of a novel red afterglow phosphor: ZrO2:Sm3+,Sn4+

A novel ZrO₂:Sm³⁺,Sn⁴⁺ phosphor is synthesized by solid state reaction. The ZrO₂:Sm³⁺ does not show afterglow. But, after doping Sn⁴⁺, intense red afterglow luminescence is firstly observed in ZrO₂:Sm³⁺,Sn⁴⁺ and it can last more than 1000 s at maximum. The afterglow decay curves of ZrO₂:Sm³⁺,Sn⁴⁺ are fitted by three exponential components and the decay process consists of initial fast, intermediate and slow decay. The thermoluminescence indicates that the Sn⁴⁺ ions induce suitable traps with the depth of 0.436 eV and result in efficient afterglow luminescence of ZrO₂:Sm³⁺,Sn⁴⁺. The thermoluminescence filling and fading experiments further confirm the important role of the proper shallow traps induced by doping Sn⁴⁺ on the afterglow of ZrO₂:Sm³⁺,Sn⁴⁺.     

Synthesis and electrical transport properties of Lu2+xTi2−xO7−x/2 oxide-ion conductors

The Lu_2+xTi_2−xO_7−x/2 (x = 0; 0.052; 0.096; 0.286; 0.44; 0.63; 33.3–49 mol% Lu₂O₃) nanoceramics with partly disordered pyrochlore-type structure are prepared by sintering freeze-dried powders obtained by a co-precipitation technique with 1600 °C annealing. Similar to pyrochlore-like compositions in the zirconate system, some of the new titanates are good oxide-ion conductors in air. The new solid-state electrolytes have oxide-ion conductivity in the interval of 1.0 × 10^− 3 – 2.5 × 10^− 3 S/cm at 740 °C in air. This value of conductivity is comparable with that of ZrO₂/Y₂O₃ ceramics. The conductivity of Lu_2+xTi_2−xO_7−x/2 depends on the chemical composition. The highest ionic conductivity is exhibited by nearly stoichiometric Lu_2+xTi_2−xO_7−x/2 (x = 0.096; 35.5 mol% Lu₂O₃) material containing ∼ 4.8 at.% Lu_Ti anti-site defects.     

Effect of calcination temperature on phase transformation,structural and optical properties of sol–gel derived ZrO2 nanostructures

Zirconia (ZrO₂) nanostructures of various sizes have been synthesized using sol–gel method followed by calcination of the samples from 500 to 700 °C. The calcined ZrO₂ powder samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infra-red spectroscopy (FT-IR), UV–visible spectroscopy (UV–vis.), Raman spectroscopy (RS) and thermogravimetric analysis (TGA). The phase transformation from tetragonal (t) to monoclinic (m) was observed. The average diameter of the ZrO₂ nanostructures calcined at 500, 600 and 700 °C was calculated to be 8, 17 and 10 nm, respectively. The ZrO₂ sample calcined at 500 °C with tetragonal phase shows a direct optical band gap of 5.1 eV. The value of optical band gap is decreased to 4.3 eV for the ZrO₂ calcined at 600 °C, which contains both tetragonal (73%) and monoclinic (27%) phases. On further calcination at 700 °C, where the ZrO₂ nanostructures have 36% tetragonal and 64% monoclinic phases, the optical band gap is calculated to be 4.8 eV. The enhancement in optical band gap for ZrO₂ calcined at 700 °C may be due to the rod like shape of ZrO₂ nanostructures. The tetragonal to monoclinic phase transformation was also confirmed by analyzing Raman spectroscopic data. The TG analysis revealed that the ZrO₂ nanostructure with dominance of monoclinic phase is found to be more stable over the tetragonal phase. In order to confirm the phase stability of the two phases of ZrO₂, single point energy is calculated corresponding to its monoclinic and tetragonal structures using density functional theory (DFT) calculations. The results obtained by theoretical calculations are in good agreement with the experimental findings.     

Monoclinic HfO2:Eu X-ray phosphor

HfO₂ and HfO₂:Eu powders were synthesized with Pechini method at temperatures in the range of 600–1500 °C. Structural, radioluminescence and photoluminescence properties of the powders were investigated. The highest light output of about 20% of the efficiency of commercial GOS:Eu was found for materials containing 0.5% of Eu and prepared at 1500 °C. The data shows, that further improvement of light output could be obtained if materials are processed at yet higher temperatures. Emission spectra indicate that Eu³⁺ experiences variety of symmetries of its surroundings. Undoped materials produce broad band emission peaking at 480 nm and showing a significant afterglow.     

Synthesis and transport studies of one-dimensional ion conductors: AxGa4+XTi1−xO8 (A = Li,Na, K)

Ion exchange reactions of the sodium-ion conductor Na_0.7Ga_4.7Ti_0.3O₈ were investigated. Exposure to molten LiNO₃ at 440 °C for 72 h resulted in a 2% decrease in the unit cell volume, whereas exposure to molten KNO₃ under similar conditions had very little effect on the lattice parameters. The electrical conductivity of unexchanged Na_0.7Ga_4.7Ti_0.3O₈ ranged from ∼ 10^− 7 S/cm at 300 °C to 10^− 3 S/cm at 1000 °C with an activation energy of 0.75 eV. Ion exchange with LiNO₃ resulted in an increase in conductivity whereas exchange with KNO₃ resulted in a decrease. The differences in conductivity are attributed to differences in the size of the mobile cation.     

Oxidation of ultra-thin Ti films on Mo(100): Soft X-ray photoelectron spectroscopy study

Titanium oxide films grown on Mo(100) have been investigated by low-energy electron diffraction (LEED) and soft X-ray photoelectron spectroscopy (PES). The film was grown by Ti deposition on Mo(100) and subsequent oxidation of the film by 12 L of O₂ exposure at room temperature. As the film was annealed at 700–1000 °C, the film in which the Ti atoms were in a Ti³⁺ oxidation state was formed. As the film was annealed at 1100–1500 °C, the oxidation state of Ti in the film was converted to Ti²⁺. The valence electronic structure of the film was measured under the condition that the emission from the Mo substrate was minimized due to a Cooper minimum of the Mo 4 d photoionization cross sections (hν = 100 eV). It was found that the Ti 3 d band in normal-emission spectra was increased in intensity when the film was annealed at 1100–1500 °C. As the film was annealed at 1300 °C for 10 s and 20 s, the film-covered Mo(100) gave (2 × 2) and (4 × 1) LEED patterns, respectively. The two-dimensional band structure of the (2 × 2) system was investigated by angle-resolved PES, and it was found that the film with a (1 × 1) periodicity with respect to the Mo(100) substrate existed in the (2 × 2) system.     

Magnetism in nanocrystalline SiC films

Magnetism been studied in two series of nanocrystalline SiC films obtained by the method of direct deposition of ions with an energy of ~100 eV at temperatures 1150 °С and 1200 °С. There were separated the contributions of diamagnetism, paramagnetism and superparamagnetism+ferromagnetism. Magnetization value of the films correlates with the deposition temperature. In the films deposited at higher temperatures the value of magnetization was by 1.5 times lower. It was concluded that induced magnetism in nanocrystalline SiC films is caused by interaction of magnetic moments of neutral V_SiV_C divacancies in separate nanocrystals. The estimated concentration of neutral V_SiV_C divacancies in nanocrystalline SiC films is ~10²⁰ сm⁻³.     

Effect of annealing on natural calcitic crystals—A thermostimulated luminescence (TSL) study

The quality crystals (Calcitic limestone) were selected using the UV–visible methylene blue adsorption method. The thermostimulated luminescence (TSL) glow curve characteristics of six well crystallized limestone samples were analyzed. The glow curves of unannealed sample show only one peak in the range 320–330 °C. The sample irradiated with a gamma dose of 100 Gy shows two additional peaks in the range of 113–125 °C and 242–260 °C when recorded with linear heating rate of 10 °C/s. The annealed sample also shows the same trend as that of irradiated sample. Annealing treatment above 250 °C increases the sensitivity of all TSL peaks except 320 °C. On the other hand, annealing at 750 °C caused a collapse in the TSL sensitivity. The enhancement in TSL sensitivity was found to depend on the annealing temperature and time. Annealing treatment at 650 °C for 4 h followed by quenching in air is the optimum condition for TSL sensitization. The response to gamma irradiation is linear in the range from 0.5 Gy to 10⁴ Gy. The emission spectra of all the samples show an emission at around 610 nm but with different intensities for each TSL peak. With reference to earlier work, it may be assumed that the recombination site always involves Mn²⁺ ions. The observation made through infra-red (IR) and X-ray diffraction (XRD) studies with thermal treatment shows the structural changes of calcite from D_3h to C_s symmetry at 750 °C. The Thermogravimetric-Differential Thermal Analysis (TG-DTA) analysis shows the calcite gets disordered at 760 °C. Hence, the collapse in the TSL sensitivity at 750 °C is due to structural change or structural disorderedness.     

Surface stoichiometry of La0.7Sr0.3MnO3 during in vacuo preparation; A synchrotron photoemission study

We present a study of the surface stoichiometry and contamination of La_0.7Sr_0.3MnO₃ thin films following exposure to air and subsequent in vacuo preparation. Samples were studied using both soft X-ray synchrotron photoemission (hν = 150 to 350 eV) and traditional Mg-Kα XPS (hν = 1253.6 eV) whilst annealing incrementally to ≈ 510°C in low pressures of O₂. In all cases, a Mn depleted and Sr rich surface oxide layer is observed, it is of reduced crystalline quality and is charge depleted. This surface layer is weakly affected by subsequent annealing, and is partially reversed by annealing in higher O₂ pressure. Surface carbon contamination is incrementally removed by annealing at increased temperatures, and at 270 °C, it is reduced to ≈ 0.4% of the topmost unit cell. The modification of the surface stoichiometry and electronic properties is consistent with the reported loss of magnetic properties in thin LSMO films.     

Characterization of Laves phase in Crofer 22 H stainless steel

This study investigated the effect of annealing temperature on the precipitation behavior of Crofer^® 22 H at 600 °C, 700 °C, and 800 °C. The grain size distribution, precipitate phase identification, and microstructure were analyzed using electron backscatter diffraction (EBSD) and energy dispersive X-ray spectroscopy (EDS). The morphology of Laves phase (Fe,Cr,Si)₂(Nb,W) precipitates having the Cr₂Nb structure changed from strip-like to needle-shaped as the annealing temperature was increased. The precipitates of the Laves phase also shifted from the grain boundaries to the grain interiors when the temperature was increased. However, the average grain size (150 μm) of the ferritic matrix did not significantly change at 600 °C, 700 °C, and 800 °C for 10 h.     

Electret properties of ethylene–propylene random co-polymer

Thermally stimulated current (TSC) spectra were examined for ethylene–propylene (EP) random co-polymer at different charging voltages V_p with positive and negative polarities. Observed TSC spectra showed two well-separated TSC bands, B_L and B_H, which respectively appeared in the temperature regions below and above 100 °C. Observed V_p dependence of B_L was quite different from that of typical polypropylene homo-polymer: As V_p increased, B_L band grew keeping its peak position same at 65 °C, and the band shape unchanged, as if the traps responsible for the B_L band are a single set of traps with the same trap depth and capture cross section. The trap depth of B_L was about 1.9 eV and 1.7 eV for positively charged EP and talc-containing EP samples, respectively. EP samples also showed unique TSC bands above 100 °C: one is a narrow TSC band peaked at 120 °C and the other is an unusual TSC band which was non-vanishing even at 165 °C just before destruction of samples by their melting. Consequently, the utmost stable charge density in EP co-polymer above 100 °C was found to be 3.5 × 10^?4 C/m² and 6.0 × 10 ^?4 C/m² for positively and negatively charged samples, respectively. These equivalent surface charge densities are much larger than those of usual polypropylene homo-polymer.     

Luminescence enhancement by the reduction–oxidation synthesis in monoclinic RE2O3 (RE=Eu,Gd) phosphors containing Eu3+ activator

A novel synthesis was developed for enhanced luminescence in sesquioxide phosphors containing Eu³⁺ activator. It consisted of two annealing steps: reduction under vacuum with gaseous H₂ at 10 Torr and 1300 °C and re-oxidation at 300–1500 °C in air. The integrated luminescence intensity of the monoclinic Eu₂O₃ phosphor was enhanced ca. 21 times by this method compared with conventional processing. The photoluminescence (PL) intensity was maximized at re-oxidation temperatures of 500–1100 °C. The PL characteristics of monoclinic Eu₂O₃ and Gd₂O₃:0.06Eu samples were compared with a commercial cubic Y₂O₃:Eu phosphor. The evolution of physical characteristics during the two-step annealing was studied by Raman spectroscopy, XPS, XRD, PL decay analysis, and SEM. PL decay lifetime increased proportionally to the PL intensity over the range 0.5–100 μs. Additional vibrational modes appeared at 490, 497, and 512 cm^?1 after the two-step annealing. The increase in PL intensity was ascribed to the formation of excess oxygen vacancies and their redistribution during annealing. Resonance crossovers between the charge transfer state and the emitting ⁵D_J states are discussed in relation to reported luminescence saturation mechanisms for oxysulfides Ln₂O₂S:Eu³⁺ (Ln=Y, La).     

Influence of rapid thermal annealing on electrical and structural properties of double metal structure Au/Ni/n-InP (1 1 1) diodes

The effect of rapid thermal annealing on the electrical and structural properties of Ni/Au Schottky contacts on n-InP have been investigated by current–voltage (I–V), capacitance–voltage (C–V), auger electron spectroscopy (AES) and X-ray diffraction (XRD) techniques. The Au/Ni/n-InP Schottky contacts are rapid thermally annealed in the temperature range of 200–500 °C for a duration of 1 min. The Schottky barrier height of as-deposited Ni/Au Schottky contact has been found to be 0.50 eV (I–V) and 0.86 eV (C–V), respectively. It has been found that the Schottky barrier height decreased with increasing annealing temperature as compared to as-deposited sample. The barrier height values obtained are 0.43 eV (I–V), 0.72 eV (C–V) for the samples annealed at 200 °C, 0.45 eV (I–V) and 0.73 eV (C–V) for those at 400 °C. Further increase in annealing temperature to 500 °C the barrier height slightly increased to 0.46 eV (I–V) and 0.78 eV (C–V) compared to the values obtained for the samples annealed at 200 °C and 400 °C. AES and XRD studies showed the formation of indium phases at the Ni/Au and InP interface and may be the reason for the increase in barrier height. The AFM results showed that there is no significant degradation in the surface morphology (rms roughness of 1.56 nm) of the contact even after annealing at 500 °C.     

Studies of ion implantation conditions and magnetic properties of MnAs nanoparticles buried in GaAs substrate

We present here results obtained on the synthesis of ferromagnetic MnAs nanoclusters embedded in a GaAs matrix. These nanoclusters are formed by co-implanting Mn+As at a dose of 1×10¹⁶ ions cm⁻² for both species. MnAs nanoclusters are only synthezised after a two-step annealing process consisting in a pre-anneal at 600 °C, 60 s which favours the solid-phase epitaxy of the amorphous implanted area. The best magnetic properties have been obtained after a second annealing at 750 °C, 15 s.     

Preparation and luminescence properties of Eu2+-doped BaSi2O5 glass-ceramics

We report on the preparation of Eu²⁺-doped BaSi₂O₅ glass-ceramics by crystallizing an Eu³⁺-doped barium-silicate glass at temperatures in the range from 750 to 1100 °C. Single phase BaSi₂O₅ glass ceramics can be obtained by thermal annealing at temperatures of about 950 °C. The luminescence intensity of Eu²⁺ increases dramatically if monoclinic BaSi₂O₅ is formed. Monoclinic Eu²⁺:BaSi₂O₅ shows efficient, broad band luminescence between 450 and 550 nm by excitation in the near UV. Annealing at temperatures >1000 °C leads to orthorhombic BaSi₂O₅ with much smaller Eu²⁺ luminescence. Static and time-resolved luminescence measurements indicate that Eu²⁺ ions are incorporated into the BaSi₂O₅ crystallites while Eu³⁺ ions remain in the amorphous phase.     

High lithium ion conductivity glass-ceramics in Li2O–Al2O3–TiO2–P2O5 from nanoscaled glassy powders by mechanical milling

Mechanical milling (MM) has been used to prepare the nanosized Li_1.4Al_0.4Ti_1.6(PO₄)₃ (denoted LATP) glassy powders, which was converted into glass-ceramics through thermal treating at 700–1000 °C. The XRD, TEM, FESEM and ac impedance techniques were used to characterize the products. The results showed that completely amorphous products were prepared by MM for 40 h, and single-phase LiTi₂(PO₄)₃-type structured glass-ceramics were obtained by further heat treatment. The lithium ion conductivity of the glass-ceramics increased with the growth of the crystalline phase and decrease of the grain size. The highest bulk conductivity (σ_b) of 1.09 × 10^− 3 S cm^− 1 with an energy of activation as low as 0.28 eV was obtained at room temperature for the specimen treated at 900 °C for 6 h. The high conductivity, easy fabrication and low cost make the LATP glass-ceramics promising to be used as inorganic solid electrolyte for all-solid-state Li-ion rechargeable batteries.     

Sonochemical assisted synthesis of SrFe12O19 nanoparticles

We present the synthesis of M-type strontium hexaferrite by sonochemistry and annealing. The effects of the sonication time and thermal energy on the crystal structure and magnetic properties of the obtained powders are presented. Strontium hexagonal ferrite (SrFe₁₂O₁₉) was successfully prepared by the ultrasonic cavitation (sonochemistry) of a complexed polyol solution of metallic acetates and diethylene glycol. The obtained materials were subsequently annealed at temperatures from 300 to 900 °C. X-ray diffraction analysis shows that the sonochemical process yields an amorphous phase containing Fe³⁺, Fe²⁺ and Sr²⁺ ions. This amorphous phase transforms into an intermediate phase of maghemite (γ-Fe₂O₃) at 300 °C. At 500 °C, the intermediate species is converted to hematite (α-Fe₂O₃) by a topotactic transition. The final product of strontium hexaferrite (SrFe₁₂O₁₉) is generated at 800 °C. The obtained strontium hexaferrite shows a magnetization of 62.3 emu/g, which is consistent with pure hexaferrite obtained by other methods, and a coercivity of 6.25 kOe, which is higher than expected for this hexaferrite. The powder morphology is composed of aggregates of rounded particles with an average particle size of 60 nm.     

Preparation of cadmium stannate films by spray pyrolysis technique

Cadmium stannate thin films were prepared by spray pyrolysis technique using cadmium acetate and tin(II) chloride precursors at substrate temperatures 450 °C and 500 °C. XRD pattern confirms the formation of orthorhombic (1 1 1) cadmium stannate phase for the film prepared at substrate temperature of 500 °C, whereas, films prepared at 450 °C are amorphous. Film formation does not occur at substrate temperature from 300 to 375 °C. SEM images reveal that the surface of the prepared Cd₂SnO₄ film is smooth. The average optical transmittance of ∼86% is obtained for the film prepared at substrate temperature of 500 °C with the film thickness of 400 nm. The optical band gap value of the films varies from 2.7 to 2.94 eV. The film prepared at 500 °C shows a minimum resistivity of 35.6 × 10⁻⁴ Ω cm.     

Oxygen diffusion studies on (Y2O3)2(Sc2O3)9(ZrO2)89

The oxygen tracer diffusion coefficient (D?) has been measured for 9 mol% scandia 2 mol% yttria co-doped zirconia solid solution, (Y₂O₃)₂(Sc₂O₃)₉(ZrO₂)₈₉, using isotopic exchange and line scanning by Secondary Ion Mass Spectrometry, as a function of temperature. The values of the tracer diffusion coefficient are in the range of 10^? 8–10^? 7 cm² s^? 1 and the Arrhenius activation energy was calculated to be 0.9 eV; both valid in the temperature range of 600–900 °C. Electrical conductivity measurements were carried out using 2-probe and 4-probe AC impedance spectroscopy, and a 4-point DC method at various temperatures. There is a good agreement between the measured tracer diffusion coefficients (D?, Ea = 0.9 eV) and the diffusion coefficients calculated from the DC total conductivity data (D_σ, Ea = 1.0 eV), the latter calculated using the Nernst–Einstein relationship.     

Crystal structure and photoluminescence correlations in white emitting nanocrystalline ZrO2:Eu3+ phosphor: Effect of doping and annealing

White emitting nanocrystalline ZrO₂:Eu³⁺ phosphors were synthesized by a simple precipitation route without using a capping agent. X-ray diffraction (XRD) study of ZrO₂ and ZrO₂:Eu³⁺samples revealed the presence of monoclinic and tetragonal phases. The monoclinic phase increases with increase in the annealing temperature while the tetragonal phase increases with increase in the concentration of Eu³⁺. This can be attributed to the presence of oxygen vacancy evolved when Zr⁴⁺ is replaced by Eu³⁺. Photoluminescence (PL) emission peaks of Eu³⁺ are observed at 591, 596, 606 and 613 nm on monitoring excitation wavelengths at 250, 286, 394 and 470 nm. The peaks at 591 and 606 nm were found to correlate with the tetragonal phase and those at 596 and 613 nm with the monoclinic phase. Intensities of these peaks are found to change as the crystal structure changes. The lifetime value corresponding to 591 nm peak increases with Eu³⁺ concentration at a particular heating temperature indicating increase of tetragonal phase with respect to monoclinic phase. The CIE co-ordinates of the doped samples were found to be close to that of white color (0.33, 0.33). The changes in the crystal structure of the doped samples due to doping and annealing did not affect the white color emission.