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1.
Y2O3: Eu3+,Tb3+ transparent, high density and optical quality thin films were prepared by the sol–gel dip-coating technique. Yttrium (III) 2,4-pentadionate was used as a precursor by its hydrolysis in ethanol. The doping agents were incorporated in the form of europium and terbium nitrate. Structural, morphological and optical properties of prepared films were investigated for different annealing temperatures in order to establish the ideal processing route that enhances the luminescent properties. X-ray diffraction (XRD) analysis shows the cubic phase for 10-layer films and annealing temperatures higher than 500°C. At 700°C, highly densified (4.52 g cm−3) and very smooth films (1.4 nm at 700°C) are produced, composed of crystallites with a grain size of 11 nm. The film thickness, refractive index and porosity, as well as the luminescent properties, were found to vary with treatment temperature.  相似文献   

2.
Ca3Al6Si2O16: Ce3+, Tb3+ phosphors have been prepared by sol–gel method. The structure and photoluminescence properties were studied with careful. The results indicated that the single-phased Ca3Al6Si2O16 phosphors crystallize at 1,000 °C for 2 h in conventional furnace. With appropriate concentrations of Ce3+ and Tb3+ ions into Ca3Al6Si2O16 matrix, these materials exhibit blue phosphors and white light under ultraviolet radiation. White-light emission can be achieved because of a 400 nm emission ascribed to transitions of Ce3+ ions and three sharp peaks at 487, 543, 585 nm, respectively, resulting from transitions of Tb3+ ions.  相似文献   

3.
Tb3+–Yb3+ co-doped Ca5(PO4)3F inverse opal photonic crystals were prepared by a self-assembly technique in combination with a sol–gel method. Upconversion luminescence characteristics of the inverse opals were investigated. The results indicate that photonic band gap has a significant effect on upconversion luminescence of Tb3+–Yb3+ co-doped Ca5(PO4)3F inverse opal. Significant inhibition of the green or blue upconversion luminescence was inspected if the photonic band gap overlapped with the emission band of Tb3+ ions.  相似文献   

4.
For the Er3+–Yb3+ codoped Al2O3 powders, the strong near-infrared photoluminescence (PL) centered at 1.535 μm derived from the energy transfer (ET) from Yb3+ to Er3+ was detected by a 978 nm laser diode excitation. Compared with that of Er3+ doped Al2O3 powders, the PL intensity enhanced about 9 times, the full width at half maximum (FWHM) extended from 82 to 90 nm, and the lifetime increased from 3.22 to 4.17 ms for Er3+–Yb3+ codoped Al2O3 powders at room temperature. The ET coefficient of 2.18 × 10−18 cm3 s−1 from Yb3+ to Er3+ was obtained based on the rate equations. The decrease of PL intensity with increasing temperature in the range of 298–733 K was observed, due to thermally enhanced nonradiative relaxation 4I13/2 → 4I15/2 dominated over thermally enhanced phonon-assisted ET in the Er3+–Yb3+ codoped Al2O3.  相似文献   

5.
Eu (0.1, 0.5 and 1.0 mol%) doped Tb3Al5O12 (TAG) was prepared by sol–gel technique through nitrate-citrate route followed by sintering in air (1,100 °C maximum temperature). XRD analysis showed that Eu3+ enters the TAG lattice substitutionally replacing the Tb3+ ion. Both XRD as well as FTIR investigation showed improvement in crystalline phase with the increase in the sintering temperature. SEM and TEM analysis showed that the powder contains the particles in 5–20 nm size with almost spherical morphology. The excitation spectrum recorded in 300–500 nm showed dominant absorption due to Tb3+ while the emission spectra recorded with 380 nm excitation had strong red emission characteristic of Eu3+. The intensity of this emission increases with the increase of the Eu concentration from 0.1 to 0.5 mol%. However, the emission intensity decreased on further increase in Eu concentration to 1.0 mol%. This intensity variation with dopant concentration is attributed to well-known “concentration quenching” observed in rare-earth doped materials. Reasonably strong red emission due to Eu was observed when excited with the blue (480 nm) radiation of a Xe lamp indicating the usefulness of the material for the realization of white light LED.  相似文献   

6.
CaAl2Si2O8: Eu2+, Mn2+ phosphors have been prepared by a sol–gel method. X-ray diffractometer, spectrofluorometer and UV–Vis spectrometer were used to characterize structural and optical properties of the samples. The results indicate that anorthite (CaAl2Si2O8) directly crystallizes at 1000 °C in the sol–gel process. CaAl2Si2O8: Eu2+, Mn2+ phosphors show two emission bands excited by ultraviolet light. Blue (around 415 nm) and yellow (around 575 nm) emissions originate from Eu2+ and Mn2+, respectively. With appropriate tuning of Mn2+ content, CaAl2Si2O8: Eu2+, Mn2+ phosphors exhibit different hues and relative color temperatures.  相似文献   

7.
8.
The Er3+–Yb3+ codoped Al2O3 has been prepared by the sol–gel method using the aluminium isopropoxide [Al(OC3H7)3]-derived Al2O3 sols with addition of the erbium nitrate [Er(NO3)3 · 5H2O] and ytterbium nitrate [Yb(NO3)3 · 5H2O]. The phase structure, including only two crystalline types of doped Al2O3 phases, θ and γ, was obtained for the 1 mol% Er3+ and 5 mol% Yb3+ codoped Al2O3 at the sintering temperature of 1,273 K. By a 978 nm semiconductor laser diodes excitation, the visible up-conversion emissions centered at about 523, 545, and 660 nm were obtained. The temperature dependence of the green up-conversion emissions was studied over a wide temperature range of 300–825 K, and the reasonable agreement between the calculated temperature by the fluorescence intensity ratio (FIR) theory and the measured temperature proved that Er3+–Yb3+ codoped Al2O3 plays an important role in the application of high temperature sensor.  相似文献   

9.
Nanostructured transparent glass-ceramics with composition of 95SiO2–5LaF3 co-doped with 0.3Yb3+, 0.1Ho3+ and 0.1Tm3+ (mol%) were synthesized by thermal treatment of precursor sol–gel derived glasses. X-ray diffraction and transmission electron microscopy analysis point out the precipitation of hexagonal LaF3 nanocrystals with diameter ranging from 11 to 20 nm in these nano-glass-ceramics. White light generation by means of efficient blue, green and red up-conversion luminescence under infrared excitation at 980 nm was observed and involved mechanisms were analyzed. Colour tuneability is achieved by varying the up-conversion emission ratios as a function of pump power.  相似文献   

10.
The effects caused by modifying additives, namely nonionic surfactants (Tween 80 and Neonol AF 9-6) and oxides (B2O3 and HfO2), on the rheology, film formation, and phase formation in the yttrium aluminum silicate system prepared by sol–gel technology were studied. The effect of 1 wt % HfO2 additions on the activation energy of crystallization was studied.  相似文献   

11.
Europium actived Lu2O3 sol–gel transparent and crack free films were deposited by dipping on silica substrates. The film microstructure was studied by waveguide Raman spectroscopy (WRS) with annealing temperatures from 400 up to 1,000 °C and X-ray diffraction. The WRS results and TEM observations were correlated and showed that crystallization of the lutetium oxide phase into cubic phase occurs at 600 °C and is stable up to 1,000 °C, the crystallite size increasing between ±38 nm with annealing temperature ranging from 600 to 1,000 °C. Opto-geometrical parameters were determined by m-lines spectroscopy using four different wavelengths of laser sources in order to confirm the step-index profile of the as-prepared waveguides. The Eu3+ doped films heat-treated at 1,000 °C presented a constant thickness for the wavelengths 493, 543, 594 and 632.8 nm and a density of 8.4 g cm−3. High-resolution X-ray images were obtained.  相似文献   

12.

Abstract  

First principle density-functional theory calculations have been carried out on the interaction of I and I3 with TiO2 anatase surfaces, modeled by finite clusters that range in size from 48 to 180 atoms. The total energy per TiO2 unit and the HOMO-LUMO gaps decrease with increasing the size of the clusters. Both redox species (I and I3 ) are strongly adsorbed on the TiO2 surface with the adsorbtion of I being stronger. Adsorption of triiodide leads to its dissociation. The positions of the HOMO and LUMO of the adsorbed systems shift negatively from their respective cluster values. Solvation effects have been modeled using the CPCM model. Introducing solvent reduces the shifting of HOMO and LUMO. Implications for dye-sensitized solar cells (DSSC) are discussed. Both the HOMO-LUMO shifting and the strong adsorption might affect the performance of the cell.  相似文献   

13.
The sequence of phases appearance during the formation of Bi1–xNdxFeO3 solid solutions in powder oxides mixtures of bismuth, neodymium, and iron has been determined. It has been shown that the closeness of the reaction mixture composition to that of the individual compound (BiFeO3 or NdFeO3) is essential for the realization of the series of phase transformations yielding solid solutions of multiferroics Bi1–xNdxFeO3 as the final product, due to the prevalence of various interphase contacts in the starting reaction zone.  相似文献   

14.
The boundaries of the glass formation region in the ternary system La2O3–As2S3–Er2O3 were found. Transparent glass of composition (La2O3)0.03(As2S3)0.90(Er2O3)0.07 was studied by X-ray photoelectron and Raman spectroscopy. The intensities of the bands characterizing As–S, La–O, and Er–O bonds increased, and these bands were shifted toward higher energies. This was due to an increase in the covalence of these bonds and probably due to the formation of new bonds in the glasses. Samples in the glass formation region are resistant at 300 K to air, water, and organic solvents.  相似文献   

15.
Pr3+ doped or Tb3+–Mg codoped CaSnO3 phosphor powder with perovskite structure was synthesized by the polymerized complex method. Powder samples crystallized into the perovskite phase at approximately 600 °C, which is 400 °C lower than the crystallization temperature for the solid-state reaction method. Uniform-sized powders with average particle sizes of 1–2 μm were obtained after heat treatment at 1,400 °C. Although the samples heat-treated at 600 °C did not exhibit photoluminescence, white photoluminescence of Pr3+ doped CaSnO3 or green photoluminescence of Tb3+–Mg codoped CaSnO3 was observed from the sample heat-treated above 800 °C. The intensity of the photoluminescence increased with increase of the heat-treatment temperature and reached a maximum for heat treatment at 1,400 °C. The maximum photoluminescence intensity for the samples prepared by the polymerized complex method was larger than those prepared by solid-state reaction method, which is probably due to the homogeneous mixing of the doped rare earth ions.  相似文献   

16.
The effect of TeO2 additions on the thermal behaviour of zinc borophosphate glasses were studied in the compositional series (100 − x)[0.5ZnO–0.1B2O3–0.4P2O5]–xTeO2 by differential scanning calorimetry, thermodilatometry and heating microscopy thermal analysis. The addition of TeO2 to the starting borophosphate glass resulted in a linear increase of glass transition temperature and dilatometric softening temperature, whereas the thermal expansion coefficient decreased. Most of glasses crystallize under heating within the temperature range of 440–640 °C. The crystallization temperature steeply decreases with increasing TeO2 content. The lowest tendency towards crystallization was observed for the glasses containing 50 and 60 mol% TeO2. X-ray diffraction analysis showed that major compounds formed by annealing of the glasses were Zn2P2O7, BPO4 and α-TeO2. Annealing of the powdered 50ZnO–10B2O3–40P2O5 glass leads at first to the formation of an unknown crystalline phase, which is gradually transformed to Zn2P2O7 and BPO4 during subsequent heating.  相似文献   

17.
A visible-light sensitive bilayered photoanode of Fe–TiO2/Zn–Fe2O3 has been developed by spray pyrolytically depositing Zn–Fe2O3 layers onto predeposited Fe–TiO2 thin film on ITO substrate. Fe–TiO2/Zn–Fe2O3 photoelectrodes were characterized by XRD, Raman, AFM, UV-vis absorption spectroscopy. Photoelectrochemical properties of bilayered Fe–TiO2/Zn–Fe2O3 photoelectrode were studied by Mott–Schottky curves and I–V characteristics. Bilayered Fe–TiO2/Zn–Fe2O3 photoelectrode was observed to possess much higher separation efficiency of photogenerated charge carriers and could generate nine times better photocurrent density than pure Fe–TiO2. Solar to hydrogen conversion efficiency exhibited by this electrode was 0.77%.  相似文献   

18.
Evidence for the existence of primitive life forms such as lichens and fungi can be based upon the formation of oxalates. These oxalates form as a film like deposit on rocks and other host matrices. The anhydrous oxalate mineral moolooite CuC2O4 as the natural copper(II) oxalate mineral is a classic example. Another example of a natural oxalate is the mineral wheatleyite Na2Cu2+(C2O4)2·2H2O. High resolution thermogravimetry coupled to evolved gas mass spectrometry shows decomposition of wheatleyite at 255°C. Two higher temperature mass losses are observed at 324 and 349°C. Higher temperature mass losses are observed at 819, 833 and 857°C. These mass losses as confirmed by mass spectrometry are attributed to the decomposition of tennerite CuO. In comparison the thermal decomposition of moolooite takes place at 260°C. Evolved gas mass spectrometry for moolooite shows the gas lost at this temperature is carbon dioxide. No water evolution was observed, thus indicating the moolooite is the anhydrous copper(II) oxalate as compared to the synthetic compound which is the dihydrate.  相似文献   

19.
Bi3+–Yb3+ ion pair co-doped YAG phosphors were successfully synthesized using conventional solid state reaction method varying the concentration of Yb3+ ions from 0.5 to 10 mol%. The optimum phosphors were characterized by powder X-ray diffraction (XRD), and surface morphology was studied with a scanning electronic microscope (SEM). The photoluminescence (PL) properties were studied with a spectrophotometers in near infrared (NIR) and ultraviolet visible (UV-Vis) regions. The synthesized phosphors can convert a photon of UV region (330 nm) into photons of NIR region (979 and 992 nm). The co-operative energy transfer (CET) was studied using a time decay curve and PL spectra. The theoretical value of quantum efficiency (QE) was calculated from steady time decay measurement, and the maximum efficiency approached up to 166.91 %. Hence, this phosphor could be used as a downconversion (DC) luminescent convertor in front of crystalline silicon solar cell (c-Si) panels to reduce heat loss due to spectral mismatch of the solar cells.  相似文献   

20.
This work proposes a new strategy to prepare a hematite (α-Fe2O3) bilayer photoanode by hydrothermally depositing α-Fe2O3 (B) on the α-Fe2O3 (A) films prepared by electrochemical deposition. Compact smooth surfaced α-Fe2O3 (A) films were electrochemically deposited on FTO (SnO2:F) substrates from an aqueous bath. The α-Fe2O3 (A), α-Fe2O3 (B), and α-Fe2O3/α-Fe2O3 bilayer films’ characteristics were defined by X-ray diffraction (XRD) measurements, field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray (EDX) spectroscopy. Pure crystalline α-Fe2O3 (B) films with a typical anisotropic-like nanoparticle formation, which exhibited nanostructured rods covering the substrate and formed the characteristic mesoporous film morphology, were hydrothermally deposited on α-Fe2O3 (A) films prepared by electrochemical depositing in a solution bath at 25 °C and a potential of ??0.15 V. The photocurrent measurements exhibited increased intrinsic surface states (or defects) at the α-Fe2O3 (A)/α-Fe2O3 (B) interface. The photoelectrochemical performance of the α-Fe2O3 (A)/α-Fe2O3 (B) structure was examined by chronoamperometry, which found that the α-Fe2O3 (A)/α-Fe2O3 (B) structure exhibited greater photoelectrochemical activity than the α-Fe2O3 (A) and α-Fe2O3 (B) thin films. The highest photocurrent density was obtained for the bilayer α-Fe2O3 (A)/α-Fe2O3 (B) films in 1 M NaOH electrolyte. This great photoactivity was ascribed to the highly active surface area, and to the externally applied bias that favored the transfer and separation of photogenerated charge carriers in α-Fe2O3 (A)/α-Fe2O3 (B). The improved photocurrent density was attributed to an appropriate band edge alignment of semiconductors and to enhanced light absorption by both semiconductors. The best performing samples were α-Fe2O3 (A)/α-Fe2O3 (B), which reached the maximum incident photon conversion efficiencies (IPCE) of 400 nm at the potential of 0.1 V. In this case, the IPCE values were 3-fold higher than those of the α-Fe2O3 (A) and α-Fe2O3 (B) films.  相似文献   

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