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1.
Optically active Er 3+:Yb 3+ codoped Y 2O 3 films have been produced on c-cut sapphire substrates by pulsed laser deposition from ceramic Er:Yb:Y 2O 3 targets having different rare-earth concentrations. Stoichiometic films with very high rare-earth concentrations (up to 5.5 × 10 21 at cm − 3) have been achieved by using a low oxygen pressure (1 Pa) during deposition whereas higher pressures lead to films having excess of oxygen. The crystalline structure of such stoichiometric films was found to worsen the thicker the films are. Their luminescence at 1.53 μm and up-conversion effects have been studied by pumping the Yb 3+ at 0.974 μm. The highest lifetime value (up to 4.6 ms) is achieved in films having Er concentrations of ≈ 3.5 × 10 20 at cm − 3 and total rare-earth concentration ≈ 1.8 × 10 21 at cm − 3. All the stoichiometric films irrespective of their rare-earth concentration or crystalline quality have shown no significant up-conversion. 相似文献
2.
Mercury is one of the most toxic heavy metals found in solid and liquid waste disposed by chloro-alkali, paint, paper/pulp, battery, pharmaceutical, oil refinery and mining companies. Any form of mercury introduced to nature through any means is converted into a more toxic form such as methylmercury chloride (as produced by aquatic organisms) which usually accumulates in the tissue of fish and birds. The primary aim of this study was to investigate performance of dithiocarbamate-anchored polymer/organosmectite composites as sorbents for removal of mercury from aqueous solution. The modified smectite nanocomposites then were reacted with carbondisulfide to incorporate dithiocarbamate functional groups into the nanolayer of the organoclay. These dithiocarbamate-anchored composites were used for the removal of mercury species [Hg(II), CH3Hg(I) and C6H5Hg(I)]. Mercury adsorption was found to be dependent on the solution pH, mercury concentration and the type of mercury species to be adsorbed. The maximum adsorption capacities were equal to 157.3 mg g−1 (782.5 μmol g−1) for Hg(II); 214.6 mg g−1 (993.9 μmol g−1) for CH3Hg(I); 90.3 mg g−1 (325 μmol g−1) for C6H5Hg(I). The competitive adsorption capacities (i.e. adsorption capacities based on solutions containing all three mercuric ions) are 7.7 mg g−l (38.3 μmol g−1), 9.2 mg g−l (42.6 μmol g−1) and 12.7 mg g−1 (45.7 μmol g−1) for Hg(II), CH3Hg(I) and C6H5Hg(I), respectively, at 10 ppm initial concentration. The adsorption capacities on molar basis were in order of C6H5Hg(I) > CH3Hg(I) > Hg(II). 相似文献
3.
Y xGd 1−xVO 4:Tm 3+ (5 mol%) phosphors were prepared by in situ co-precipitation technology with the different content ratio of Y/Gd ( x = 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, respectively). During the process, rare earth coordination polymers with o-hydroxylbenzoate were used as precursors, composing with polyethylene glycol (PEG) as dispersing media. After heat-treatment of the resulting multicomponent hybrid precursors at 900 °C, the samples were obtained. SEM indicated the particles present good crystalline state, whose crystalline grain sizes were about 0.2–2 μm. Under the excitation of 257 nm, all the materials show the characteristic emission of Tm 3+ which is the strong blue emission centered at 475 nm originating from 1G 4 → 3H 6 of Tm 3+. Besides this, concentration quenching appears in the system of YVO 4:Tm 3+ and GdVO 4:Tm 3+. And when x reaches 0.5, the system of Y xGd 1−xVO 4:Tm 3+ shows the strongest blue emission. 相似文献
4.
Since we presented our preliminary result (Nucl. Instr. and Meth. A 486 (2002) 170) at SCINT2001, we have continued our efforts to increase the light yield (LY) of PbWO 4 scintillators by extending different dopings with an aim to find a possibility of using PbWO 4 successfully in Positron Emission Tomography (PET). Overall result obtained for single doping as well as double and tripple co-dopings are summarized, including decay characteristics and radiation hardness. The LY in non-doped PbWO 4 crystals with a size of 10×10×(20–30) mm 3 is 25–35 photolectrons/MeV (phe/MeV) corresponding to 3–4% of the LY in BGO, when measured with a bialkali photomultiplier during a gate of 1 μs. The maximum LY increased to 49 phe/MeV for single doping with Mo 6+, 80 phe/MeV for double co-doping of Mo 6++Sb 5+, and 85 phe/MeV for tripple co-doping of Mo 6++Cd 2++Sb 5+. The radiation hardness is larger than 10 5 Gy for each of the samples co-doped with Mo 6++Sb 5+ and Mo 6++Cd 2++Sb 5+, while it is much poorer in PWO:Mo 6+. In each of these co-doped samples, a medium-speed green emission in the microsecond range is created besides the fundamental fast (a few nanoseconds range) blue one, giving a peak at 500 nm in the radioluminescence spectrum similarly as in PWO:Mo 6+. 相似文献
5.
Ferroelectric SrBi 2Ta 2O 9/SrBi 2Nb 2O 9 (SBT/SBN) multilayer thin films with various stacking periodicity were deposited on Pt/TiO 2/SiO 2/Si substrate by pulsed laser deposition technique. The X-ray diffraction patterns indicated that the perovskite phase was fully formed with polycrystalline structure in all the films. The Raman spectra showed the frequency of the O–Ta–O stretching mode for multilayer and single layer SrBi 2(Ta 0.5Nb 0.5) 2O 9 (SBNT) samples was 827–829 cm −1, which was in between the stretching mode frequency in SBT (813 cm −1) and SBN (834 cm −1) thin films. The dielectric constant was increased from 300 (SBT) to 373 at 100 kHz in the double layer SBT/SBN sample with thickness of each layer being 200 nm. The remanent polarization (2 Pr) for this film was obtained 41.7 μC/cm 2, which is much higher, compared to pure SBT film (19.2 μC/cm 2). The coercive field of this double layer film (67 kV/cm) was found to be lower than SBN film (98 kV/cm). 相似文献
6.
Gamma-ray irradiation induced color centers and charge state recharge of impurity and doped ion in 10 at.% Yb:YAP have been studied. The change in the additional absorption (AA) spectra is mainly related to the charge exchange of the impurity Fe 2+, Fe 3+ and Yb 3+ ions. Two impurity color center bands at 255 and 313 nm were attributed to Fe 3+ and Fe 2+ ions, respectively. The broad AA band centered at 385 nm may be associated with the cation vacancies and F-type center. The transition Yb 3+ → Yb 2+ takes place in the process of γ-irradiation. Oxygen annealing and γ-ray irradiation lead to an opposite effect on the absorption properties of the Yb:YAP crystal. In the air annealing process, the transition Fe 2+ → Fe 3+ and Yb 2+ → Yb 3+ take place and the color centers responsible for the 385 nm band was destroyed. 相似文献
7.
Optimum thickness of charge stripper foils installed at the terminal of a tandem accelerator has been investigated from the view of (1) charge stripping effect, (2) transmission of ions through accelerator, (3) lifetime of foils for the irradiation of ions. For this purpose, measurements have been done for (a) transmission of H, Li, O, Br and Au ions, passing through 12 UD Pelletron tandem accelerator for carbon stripper foils of 1.8–19.5 μg/cm 2 thickness, at terminal voltages of 5 and 10 MV, and (b) lifetime of 2–15 μg/cm 2 thick Tanashi foils developed by Sugai by irradiating Au ions at the terminal voltage of 10 MV. The results obtained are as follows: (a) From the view of above items (1) and (2), the optimum thickness of foils is 10 μg/cm 2 for ions of Z=1, several μg/cm 2 for Z=8, and less than a few μg/cm 2 for heavier ions. (b) From the view of item (3), the lifetime of Tanashi foils by means of new arc-discharge method is demonstrated to be much longer than that of commercial foils for foils thicker than about 5 μg/cm 2 thick. This superiority rapidly decreases with decreasing foil thickness, and at around 2 μg/cm 2, the lifetime of Tanashi foils is at the most 2.4 times longer than that of commercial foils. 相似文献
8.
Nd 3+ : YVO 4 is one of the most interesting laser hosts for micro and diode-pumped solid state lasers. We have studied magnetic and optical properties of Nd 3+ in three zircon type crystals YMO 4 (M=V, As, P). In particular, Nd 3+ ions exhibit in the three hosts a multisite character observed in the absorption and emission spectra. However, the emission and its dynamics are strongly dependant on the reabsorption mechanisms. In Nd : YVO 4, single crystals containing 7 ± 1 × 10 18 Nd 3+ ions/cm 3, the lifetime is 95 ± 2 μs in good agreement with the calculated radiative lifetime. Electron Paramagnetic Resonance (EPR) measurements are performed to identify the nature of the different substitution sites for Nd 3+ ions. Nd 3+ ions are found to be inhomogeneously distributed in tetragonal D 2d symmetry sites, in isolated ions, “shallow clusters” and pairs. Proportions of the different local environments depend on the total neodymium concentration. For instance, 15% of the Nd 3+ ions are gathered in Nd 3+–Nd 3+ pairs for 7.2 ± 0.2 × 10 19 Nd 3+ ions/cm 3. 相似文献
9.
A complete spectroscopic investigation of energy transfer processes in oxyfluoride glass ceramics containing CaF 2 nano-crystals doped with various amounts of Er 3+ and Yb 3+ was reported. An enhancement of the 1.53 μm emission and infrared to visible up-conversion fluorescence was confirmed experimentally due to efficient non-radiative energy transfer from Yb 3+ to Er 3+ ions concentrated in CaF 2 nano-crystals. The efficiency of Yb 3+ to Er 3+ energy transfer in excess of 85% was obtained for 0.5 mol% Er 3+/2.0 mol% Yb 3+ co-doped glass ceramic. Using rate equation formulism, the coefficient of Yb 3+ to Er 3+ energy transfer was determined to be about 3.5 times higher than that of Er 3+ to Yb 3+ energy back transfer, which is sufficient to provide high 4I 11/2 population of Er 3+ to improve the fluorescence of the co-doped glass ceramics. 相似文献
10.
The purpose of this study was to investigate the use of foam fractionation to recover valuable surfactant (SDS) and metal ion (Cd 2+) in the permeate of micellar-enhanced ultrafiltration (MEUF). The effects of operating factors, such as time, air flow rate, feed flow rate, liquid height, foam height, feed surfactant concentration, ethanol concentration and temperature on separation characteristics were studied in the continuous operation. When the concentrations of surfactant (SDS) and metal ion (Cd 2+) in the feed solution were 500 mg/L and 10 mg/L, an enrichment ratio of 3.1 was achieved for SDS along with 52% removal fraction, as well as 99.35% Cd 2+ was removed, after optimization of different process parameters. As the optimized results, the air and liquid flow rates were 100 L/h and 5 L/h, liquid and foam heights were 45 cm and 66 cm, respectively, sparger pore size was 10 μm. The Cd 2+ concentration in the effluent was lower than 0.1 mg/L which could meet the integrated wastewater discharge standard (the first grade of national discharge standards in China). 相似文献
11.
The process of energy transfer from divalent manganese to trivalent praseodymium ions is studied with the help of Forster–Dexter theory. Some of the important energy transfer parameters such as transfer probability ( PSA), quantum yield of energy transfer ( μ), critical radius ( R0) and critical concentration of the acceptor ( CA) are evaluated for the energy transfer pairs Mn 2+ : Pr 3+, Pr 3+ : Pr 3+ in phosphate glasses. The transfer of energy from Mn 2+ to Pr 3+ was confirmed by recording the fluorescence decay curves of Mn 2+ emission corresponding to various activator concentrations which show a non-exponential behaviour. Large values of transfer probabilities and transfer efficiencies suggest that Mn 2+ ion can act as a good sensitizer to Pr 3+ ion in phosphate glass. 相似文献
12.
An optimized and validated spectrophotometric method has been developed for the determination of uranyl ion in the presence of other metal ions. The method is based on the chelation of uranyl ion with meloxicam via β-diketone moiety to produce a yellow colored complex, which absorbs maximally at 398 nm. Beer's law is obeyed in the concentration range of 5–60 μg/mL with apparent molar absorptivity and Sandell's sensitivity of 5.02 × 10 4 L/mol/cm and 0.1 μg/cm 2/0.001 absorbance unit, respectively. The method has been successfully applied for the determination of uranyl ion in synthetic mixture and soil samples. Results of analysis were statistically compared with those obtained by Currah's spectrophotometric method showing acceptable recovery and precision. 相似文献
13.
The non-linear optical properties of metal-free phthalocyanine (MFPC) thin films were examined using the second harmonic at 532 nm from a pulsed Nd:YAG laser, and the continuous wave He–Ne and Ar + lasers. The He–Ne laser transmission at fixed input intensity was found to increase temporally within a period of 12 h. The third-order non-linear susceptibilities ( χ(3)) by four-wave mixing were measured for films of different thickness. The saturation intensity of MFPC, and its absorption cross-section, at 633 nm from a He–Ne laser, are reported. An optical bistability was recorded using a He–Ne laser. An AND logic gate was also demonstrated in the system. These phenomena in the system are attributed to refractive index modulation by thermal excitations. 相似文献
14.
It has been found that charge compensated CaMoO 4:Eu 3+ phosphors show greatly enhanced red emission under 393 and 467 nm-excitation, compared with CaMoO 4:Eu 3+ without charge compensation. Two approaches to charge compensation, (a) 2Ca 2+ → Eu 3+ + M +, where M + is a monovalent cation like Li +, Na + and K + acting as a charge compensator; (b) 3Ca 2+ → 2Eu 3+ + vacancy, are investigated. The influence of sintering temperature and Eu 3+ concentration on the luminescent property of phosphor samples is also discussed. 相似文献
15.
The effect of radiation trapping on the emission properties of Er 3+-doped tellurite and phosphate glasses has been investigated as the function of sample thickness and doping concentration. It was found that radiation trapping exists generally in two glass matrices, even at low doping concentration (0.1 mol% Er 2O 3). The larger effect of radiation trapping in tellurite glasses compared with phosphate glasses is due to its larger emission cross-section at 1.5 μm band and the spectral overlap between the emission and absorption spectra of Er 3+: 4I 13/2 ↔ 4I 15/2transition. Due to radiation trapping, the measured lifetime of the Er 3+: 4I 13/2 level in tellurite glasses increases by about 11–37% with increasing the sample thickness at the different erbium doping concentration, while 6–17% for phosphate glasses. And the full-width at half maximum of fluorescence (FWHM) of Er 3+: 4I 13/2 → 4I 15/2 transition in tellurite glasses increased by about 15–64% with increasing the sample thickness, while 11–55% for phosphate glasses. It caused a high overestimation on the figure of merits (FOM) for amplifier bandwidth ( σe × FWHM). 相似文献
16.
Rate equations formalism is used to predict the population ratio of the Er 3+ 4I 13/2 levels involved in the 1.55 μm laser transition in the Yb:Er:CAS laser materials. An effective Yb → Er energy transfer, favourable to the Er 3+ 1.55 μm laser emission, is demonstrated in this laser host. Indeed, the Yb → Er transfer and the Er → Yb back transfer rates are calculated to be 6 x 10 −16 and 0.45 x 10 −16 cm 3 s −1, respectively. Attempts of codoping the system with Nd 3+, Eu 3+ and Ce 3+ have been realised in order to increase the population of the Er 3+ 4I 13/2 laser emitting level. Best results are obtained with Ce 3+ ion since in the sample containing 6 x 10 20 Ce 3+/cm 3, the Er 3+ 4I 11/2 level lifetime is divided by a factor of 3 while the Er 3+ 4I 13/2 fluorescence lifetime remains unaffected. On the contrary, codoping with Nd 3+ or Eu 3+ ions simultaneously decreases the Er 3+ 4I 11/2 and 4I 13/2 kinetics parameters. The role of the other parameters such as Yb/Er concentrations ratios is also discussed. 相似文献
17.
A simple method for positive and negative ion species measurements utilizing ion bursts is presented. In this ion-burst method, the ion bursts are excited by a potential applied to a mesh grid immersed in the plasma. Since the velocity of the ion burst is dependent on the excitation voltage and the ion mass, the ion species can be determined from measurement of the ion-burst velocity. In the DC discharge of an Ar/SF 6 gas mixture, the positive ion species are found to be Ar +, SF 3+ and SF 5+, and the negative ion species are found to be F − and SF 6−. These results are compared with the spectrum analysis using a quadrupole mass spectrometry system and show qualitative agreement with them. 相似文献
18.
The spectra of electron paramagnetic resonance (EPR) of fluoroaluminate glass (FAG-36) based on mineral usovite Ba 2CaMgAlF 14 were studied. The paramagnetic centers responsible for EPR signals were induced by ion bombardment of the substrates prepared from this glass. The N +, O +, Ar + and Pb + ions with energy E = 150 keV were used. The integrated dose D was 2 × 10 16 ions/cm 2. It is shown by means of isochronal anneal experiments and computer simulation of the EPR spectra that they contain four components: broad Gaussian line (GL) with g = 2.016 and σ oscillating in the range 30–40; two anisotropic spectra with gz = 2.016, gy = 2.009; gx = 2.001 (FA 1) and gz = 2.045; gy = 2.010; gx = 1.98 (FA 2) as well as narrow isotropic line of Lorentzian shape with g = 2.0025 and Δ H = 0.6 mT. The comparison of obtained results with literature data for γ-irradiated fluoride glasses and ion-implanted oxide glasses of different compositions permitted to conclude that GL is due to hole defects typical of fluoride glasses and localized on several anions (fluorines and oxygen(s)); anisotropic FA 1- and FA 2-spectra are attributed to molecular 0 2−-ions, and narrow isotropic signal is supposedly assigned to big molecular ions (O 2O −, 0 4− , CO +, CO −) located in voids of damaged implantation layer. 相似文献
19.
The saturation of the optical absorption in V 3+ : YAG crystal is investigated. The absorption cross section of tetrahedral V 3+ at 1.08 μm is estimated to be 8.2±2.5x10 -18 cm 2. Q-switching and passive mode-locking for a number of solid state lasers with wavelengths at 747 nm, 780 nm, 1.06 μm and 1.34 μm have been obtained with a V 3+ :YAG saturable absorber. 相似文献
20.
Single-crystal ZnWO 4:Dy 3+ was grown by Czochralski technique. The XRD, absorption spectra as well as fluorescence spectrum are investigated and the Judd–Ofelt intensity parameters Ω2, Ω4, Ω6 are obtained to be 7.76 × 10 −20 cm 2, 0.57 × 10 −20 cm 2, 0.31 × 10 −20 cm 2, respectively. Calculated radiative transition rate, branching ratios and radiative lifetime for different transition levels of ZnWO 4:Dy 3+ crystals are presented. Fluorescence lifetime of 4F 9/2 level is 158 μs and quantum efficiency is 66%.The most intense fluorescence line at 575 nm correlative with transition 4F 9/2 → 6H 13/2 is potentially for application of yellow lasers. 相似文献
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