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1.
Sequential multi-energy implantations of zinc and sulphur ions have been performed in a 250-nm thick SiO2 layer thermally grown on 1 1 1 silicon. Energies and doses have been chosen to produce 10 at.% constant concentration profiles overlapping over about 100 nm. Manganese is subsequently introduced at various levels by the same way. Thermal treatments (from 700 to 1100 °C) lead to the formation of nanometric precipitates of the luminescent compound ZnS:Mn. A bimodal size distribution is observed, with a quasi-single layer of large particles (40 nm) in the end-of-range region and much smaller precipitates between this layer and the surface. The orange emission is maximal when the Mn concentration is close to 3%. Several hours at 900 °C is the best thermal budget for maximal luminescence intensity at room temperature. A shift of the excitation spectrum related to size variations, shows that the particles of smaller size are mainly responsible for the observed luminescence. In agreement with other authors, the luminescence lifetime is found in the ms range and increases with the nanocrystal diameter, tending to the lifetime of bulk ZnS. The luminescence of ZnS:Mn nanoparticles embedded in SiO2 by ion implantation is also shown to be very stable during long UV light irradiation. 相似文献
2.
Mn2+-doped Zn2SiO4 and Mg2Gd8(SiO4)6O2 phosphor films were deposited on silicon and quartz glass substrates by sol–gel process (dip-coating). The variations of sol viscosity with time and film thickness with the number of layers were investigated in Zn2SiO4: Mn system. The results of XRD and IR showed that the Zn2SiO4: Mn films remained amorphous below 700°C and crystallized completely around 1000°C. From AFM studies, it was observed that the grains with 0.5–0.8 μm size packed closely in Zn2SiO4: Mn films, which were uniform and crack free. The luminescence properties of Zn2SiO4: Mn films were characterized by absorption, excitation and emission spectra as well as luminescence decay. These properties were discussed in detail by a comparison with those of Mn2+ (and Pb2+)-doped Mg2Gd8(SiO4)6O2 phosphor films. 相似文献
3.
Motlan Guanghua Zhu K. Drozdowicz-Tomsia K. McBean M.R. Phillips E.M. Goldys 《Optical Materials》2007,29(12):1579-1583
ZnS nanocrystals (NCs) capped with tetramethylammonium (TMAH) were synthesized from ZnCl2 · 2H2O and thiourea using a wet chemical process. Further treatments of the nanocrystals such as aging, and annealing have been conducted to examine the stability of the grown samples. The X-ray diffraction spectra show that the crystal has a zinc blende structure with particle size of about 2 nm. The evidence of nanocrystalline character is also clear in the UV–Vis absorption that shows an excitonic peak at about 236 nm (5.2 eV) arising from band edge transitions. A photoluminescence emission peak centered at about 450 nm (2.7 eV) is attributed to transitions between shallow donors and Zn+ vacancies. Both absorption and photoluminescence spectra show that sample aging does not affect the characteristics of the sample, possibly due to protection by TMAH capping. Annealing at 700 °C and 900 °C results in the red shift of the photoluminescence. 相似文献
4.
This paper presents the observations of the study on arsenic removal from a contaminated ground water (simulated) by adsorption onto Fe3+ impregnated granular activated carbon (GAC-Fe). Fe2+, Fe3+ and Mn2+ have also been considered along with arsenic species in the water sample. Similar study has also been done with untreated granular activated carbon (GAC) for comparison. The effects of adsorbent dose, particle size of adsorbent and initial arsenic concentration on the removal of As(T), As(III), As(V), Fe2+, Fe3+ and Mn2+ have been discussed. Under the experimental conditions, the optimum adsorbent doses for GAC-Fe and GAC have been found to be 8 g/l and 24 g/l, respectively with an agitation time of 15 h. Particle size of the adsorbents (both GAC and GAC-Fe) has shown negligible effect on the removal of arsenic and Fe species. However, for Mn removal the effect of adsorbent particle size is comparatively more. Percentage removal of As(T), As(V) and As(III) increase with the decrease in initial arsenic concentration (As0). However, the increase in percentage removal of all the arsenic species with decrease in As0 are less for higher value of As0 (3000–500 ppb) than those of the lower value of As0 (500–10 ppb). The % removal of As(T), As(III), As(V), Fe, and Mn were 95%, 92.4%, 97.6%, 99% and 41.2%, respectively when 8 g/l GAC-Fe was used at the As0 value of 200 ppb. However, for GAC these values were 55.5%, 44%, 71%, 98% and 97%. The pH and temperature of the study were 7 ± 0.1 and 30 ± 1 °C, respectively. 相似文献
5.
Guocong Liu Xuechen Duan Haibin Li Dawen Liang 《Materials Chemistry and Physics》2008,110(2-3):206-211
GaOOH:Eu3+ nanorods with different aspect ratios were prepared by hydrothermal method at 140 °C. - and β-Ga2O3:Eu3+ were converted from as-prepared GaOOH:Eu3+ particles by calcination at 500 and 850 °C, respectively. The products were characterized with X-ray diffraction (XRD), transmission electron microscope (TEM) and photoluminescence (PL). Results show that solution pH values play a key role in the formation of the GaOOH:Eu3+ powders with different morphologies and - and β-Ga2:Eu3+ inherit the morphology of GaOOH:Eu3+ exactly. The photoluminescence characteristics of β-Ga2O3:Eu3+ were also investigated. Experimental results reveal that the color purity of β-Ga2O3:Eu3+ nanorods with high aspect ratio is enhanced in comparison with β-Ga2O3:Eu3+ nanorods with low aspect ratio. 相似文献
6.
Carbon-based nanoparticles synthesized by heat treatment of nanodiamond in the temperature range of 1000–1900 °C were added to PTFE film to investigate the structural effect of the carbon particles on the tribological properties of PTFE composite film. Carbon-based nanoparticles were prepared by milling with micron sized beads in chemically treated water before their addition to PTFE film. The wear and frictional properties of PTFE nanocomposite film were measured by the ball on plate type wear test. The wear resistance of PTFE film was found to be enhanced by the addition of 2 wt% of carbon nanoparticles. The wear coefficient of PTFE film was decreased from 16.2 to 3.5 × 10−6 mm3/N m by the addition of carbon-based nanoparticles heat-treated at 1000 °C. Increasing the heating temperature of the nanodiamonds caused the extent of aggregation and particle size to increase. The wear resistance of PTFE nanocomposite film was enhanced by the addition of nanodiamonds heat-treated at 1000 °C, but decreased when the heat treatment temperature of carbon nanoparticles was further increased. Tribological behavior of PTFE nanocomposite films depending on the types of carbon nanoparticles were explained based on the structural, physical and chemical modification of carbon nanoparticles. 相似文献
7.
Yong Jae Suh Hee Dong Jang Han Kwon Chang Dae Won Hwang Heon Chang Kim 《Materials Research Bulletin》2005,40(12):2100-2109
We investigated the chemical kinetics of NiCl2 reduction to apply to the synthesis of nickel nanoparticles in a tubular furnace reactor. The conversion of NiCl2 increased monotonically with reaction temperature up to 99% at 950 °C, and in turn, the rate constant of the reaction increased from 78 to 286 with an increase in the temperature from 800 to 950 °C. The reaction rate was estimated to be the first order with respect to chloride concentration, and the rate constant obeyed the Arrhenius law, of which the activation energy and pre-exponential factor were 103.79 kJ/mol and 7.34 × 106 min−1, respectively. Taking advantage of the kinetics, we synthesized crystalline nickel nanoparticles with average primary particle size ranging from 31 to 106 nm by systematically controlling the reactor temperature and chloride concentration. 相似文献
8.
采用水热法制备了ZnS∶Mn,Cu电致发光材料,利用透射电镜对发光材料的结构和形貌进行表征,并且探讨了Cu2+、Mn2+掺杂量和反应温度对ZnS∶Mn,Cu发光材料亮度的影响。结果显示,随着Cu2+、Mn2+掺杂量的增加,发光材料的亮度也随之增加,但对于Cu2+、Mn2+掺杂都存在最佳值,当Cu2+掺杂量0.2%,Mn2+掺杂量4%,温度150℃时,得到的电致发光材料亮度较高,粒径约10nm左右。 相似文献
9.
The effect of β-spodumene additions on the in situ phase formation and abundances in an Al2O3–Al2TiO5 system in the temperature range 1000–1400 °C has been studied by neutron diffraction and differential thermal analysis. Results show that β-spodumene began to decompose by phase separation and partial melting at 1290 °C, followed by complete melting at 1330 °C. Formation of Al2TiO5 was observed to occur at 1310 °C and its abundance increased with temperature. The addition of β-spodumene as a sintering aid did not cause its reaction with alumina or rutile to form additional phases. Addition of β-spodumene in excess of 5 wt% resulted in pronounced vitrification, which partly recrystallised when cooled to room temperature. The temperatures of Al2TiO5 formation and melting of β-spodumene are consistent with the results of differential thermal analysis. 相似文献
10.
Nanoparticles of ZnS:Mn have been grown by radio frequency magnetron sputtering technique on glass and Si substrates at a substrate temperature 300 K. X-ray diffraction patterns and selected area electron diffraction patterns confirmed the nanocrystalline cubic ZnS phase formation. TEM micrographs of the films revealed the manifestation of ZnS:Mn nanoparticles with an average size 6 nm. UV–Vis–NIR spectrophotometric measurement showed that the films are highly transparent (90%) in the wavelength range 400–2600 nm. From the measurements of transmittance spectra of the films the direct allowed bandgap values have been calculated and they lie in the range 3.89–4.12 eV. The bandgap decreased with the increase of Mn concentration in the films. The Mn concentrations in the films have been varied from 0% to 8.9% and was measured by energy dispersive X-ray analysis. The photoluminescence of the Mn doped ZnS nanoparticles was measured. The intensity of the PL peaks at first increased with the increase of Mn concentration in the films up to 3.8% of Mn doping and at a Mn concentration higher than this, the intensity of PL peak decreased. Nanocrystalline ZnS:Mn showed good field emission property with a turn on field lying in the range 5.26–6.78 V/μm for a variation of anode to sample distance from 60 μm to 100 μm. 相似文献
11.
Kyoung Il Moon Hyun Seon Hong Kyung Tae Hong Kyung Sub Lee Seon Jin Kim 《Materials Science and Engineering: A》2004,380(1-2):46-51
The mechanically alloyed (Al + 12.5 at.% Cu)3Zr powders were consolidated by cold isostatic pressing (CIP) and subsequent sintering. Effects of CIP pressure and sintering temperature on the stability of metastable L12 phase and nanocrystalline structure were investigated. Before sintering, the powders were CIPed at 138, 207, 276, and 414 MPa. The relative densities of the CIP compacts were not greatly affected by the CIP pressure. However, the L12 phase of the specimen CIPed at pressures greater than 276 MPa was partially transformed into D023. The optimum consolidation conditions for maintaining L12 phase and nanocrystalline microstructure were determined to be CIP at 207 MPa and sintering at 800 °C for 1 h for which the grain size was 34.2 nm and the relative density was 93.8%. Full density specimens could be prepared by sintering above 900 °C, however, these specimens consisted of L12 and D023 phases. The grain sizes of all the specimens were confirmed by TEM and XRD, and were found to be less than 40 nm. This is one of the smallest grain sizes ever reported in trialuminide intermetallic compounds. 相似文献
12.
Iron oxide nanoparticles for biomedical applications in the size range of 15–130 nm were prepared by either oxidative hydrolysis of ferrous sulfate with KOH or precipitation from ferrous/ferric chloride solutions. The magnetite particle size is controlled by variation of pH and temperature. The synthesized magnetite nanoparticles are partially oxidized as signaled by ferrous concentrations of below 24 wt% Fe2+ and lattice parameters of a0 ≤ 8.39 Å which are smaller compared to 8.39 Å for stoichiometric magnetite. The extend of oxidation increases with decreasing particle size. Heating at 150–350 °C topotactically transforms the magnetite nanoparticles into stoichiometric tetragonal maghemite (ferrous ion concentration cFe2+=0 and a0 = 8.34 Å) without significant particle growth. The magnetite–maghemite transformation is studied with thermal analysis, XRD and IR spectroscopy. The saturation magnetizations of the magnetite and maghemite particles decrease with decreasing particle size. The variation of Ms with particle size is interpreted using a magnetic core–shell particle model. Magnetite particles with d ≤ 16 nm show superparamagnetic behavior at room temperature whereas particles with diameter >16 nm display hysteresis behavior. These particles are candidates for biomedical applications, e.g. controlled drug release or hyperthermia. 相似文献
13.
The sol-gel method was used to obtain a kind of white-light emitting ZnS:Mn2+ nanoparticles capped by methacrylic acid with an average particle size of approximately 7 nm. The photoluminescence spectra, X-ray diffraction spectra, Fourier transform infrared reflection spectra and ultraviolet absorption spectra were used to measure their optical properties and crystal structures. The ZnS:Mn2+ nanoparticles with 0.58 wt% Mn2+ concentration emitted white light when excited by 380 nm. The PL spectrum exhibits two emission peaks under irradiation: one at 480 nm generated from the ZnS matrix, and one at 590 nm emitted by the doped Mn2+ ions. The nanoparticles will only emit white light with the optimum Mn2+ concentration (0.58 wt%). X-ray diffraction demonstrates the synthesized ZnS:Mn2+ nanoparticles have zinc blend crystal structure, and the infrared patterns of the capped ZnS:Mn2+ nanoparticles and methacrylic acid are comparable, indicating that the methacrylic polymer has capped or modified ZnS:Mn2+ nanoparticles. 相似文献
14.
B.A. Marinkovic P.M. Jardim E. Morgado Jr. M.A.S. de Abreu G.T. Moure F. Rizzo 《Materials Research Bulletin》2008,43(6):1562-1572
BaTi3O7·nH2O nanotubes have been synthesized through a hydrothermal reaction between Na-rich trititanate nanotubes and Ba(OH)2 within the pH range 12–8.2. These nanotubes possess the same layered crystal structure of the precursor Na2−xHxTi3O7·nH2O. They also keep the morphology of their precursor Na-trititanate nanotubes used in the synthesis, having an external diameter of 20–25 nm. The BaTi3O7·nH2O nanotubes remained fully stable up to 300 °C, while nanotubular form continues to exist up to 600 °C, together with amorphous particles. 相似文献
15.
Glass-free LTCC microwave dielectric ceramics 总被引:2,自引:0,他引:2
The sintering behavior, microstructure and microwave dielectric properties of complex pyrophosphate compounds AMP2O7 (A = Ca, Sr; M = Zn, Cu) were investigated in this paper. All compounds could be densified below the temperature of 950 °C without any glass addition, and exhibit low permittivity (r < 8), high Q × f value and negative temperature coefficient of resonant frequency. The Q × f value was discussed from the point of view of bond strength. The chemical compatibility with silver and copper was also investigated. All compounds seriously react with silver at 700 °C. However SrZnP2O7 could be co-fired with copper in reduced atmosphere. The microwave dielectric properties of SrZnP2O7 sintered at 950 °C in reducing atmosphere are: r = 7.06, Q × f = 52781 GHz, τf = −70 ppm/°C. In terms of its lower sintering temperature, chemical compatibility with copper and good microwave dielectric properties, SrZnP2O7 ceramic is very promising for low temperature co-fired ceramic (LTCC) applications. 相似文献
16.
A spray pyrolysis process was used to prepare spherical yttrium aluminum garnet (Y3Al5O12:Tb) phosphor particles with enhanced luminescence properties. The aim of the process was to improve the morphology and luminescent intensity of the Y3Al5O12:Tb phosphor particles by modifying the precursor solution. The particles produced from a nitrate aqueous solution were spherical with a hollow structure that was deformed by the post treatment at 1400 °C. To avoid the hollowness, the nitrate solution was modified by the addition of an NH4OH solution so that a polycation solution could be obtained. Compared with the hollow particles prepared from the nitrate aqueous solution, the Y3Al5O12:Tb particles with the spherical morphology and nonaggregated structure, even after the post treatment, were successfully prepared and found to have an improved photoluminescence and cathodoluminescence intensity. 相似文献
17.
Piezoelectric powders and ceramics with the composition of Pb0.95Sr0.05(Zr0.52Ti0.48)O3–Pb(Zn1/3Nb2/3)O3–Pb(Mn1/3Sb2/3)O3 (PZT–PZN–PMS) were prepared by molten salt synthesis (MSS) and conventional mixed-oxide (CMO) methods, respectively. The influence of synthesis process on the properties of powders and ceramics were investigated in detail. The results show that the MSS method significantly improved the sinterability of PZT–PZN–PMS ceramics, resulting in an improvement of dielectric and piezoelectric properties compared to the CMO method. The optimum values of MSS samples are as follows: r = 1773; tan δ = 0.0040; Tc = 280 °C; d33 = 455 pC/N; kp = 0.70; Qm = 888; Ec = 10.3 kV/cm; and Pr = 28.2 μC/cm2, at calcination of 800 °C and sintering of 1120 °C temperature. 相似文献
18.
Zhang J Su F Chen W Sammynaiken R Westcott SL McCready DE Li G Joly AG 《Journal of nanoscience and nanotechnology》2005,5(9):1465-1471
Efficient green emission from ZnMgS:Mn2+ nanoparticles prepared by co-doping Mg2+ and Mn2+ ions into ZnS lattices has been observed. The synthesis is carried out in aqueous solution, followed by a post-annealing process, thus showing the features of less complexity, low cost, and easy incorporation of dopants. In comparison with the emission of ZnS:Mn2+ nanoparticles, which is located generally around 590 nm, the photoluminescence of ZnMgS:Mn2+ nanoparticles is blue-shifted by 14 nm in wavelength, leading to the enhanced green emission. The X-ray diffraction, electron spin resonance, and pressure dependent photoluminescence measurements suggest that the change of the crystal field caused by Mg2+ ionic doping and the lower symmetry in the nanoparticles may account for the blue-shift of the photoluminescence. The ZnMgS:Mn2+ nanoparticles with 1% Mn2+ doping exhibit the strongest luminescence, which could potentially meet the requirements for the construction of green light emitting diodes. 相似文献
19.
Fe3C nanoparticles encapsulated in carbon shell with a size range of 20–50 nm were obtained in large scale by reacting anhydrous FeCl3, hexamethylenetetramine and metal Na in an autoclave at 650 °C. Magnetization measurements show that the as-obtained materials display superparamagnetic properties at room temperature. A possible formation mechanism of the core–shell nano-structures was discussed. 相似文献
20.
Harumitsu Nishikawa 《Materials Letters》2001,50(5-6):364-370
The thermal behavior of stoichiometric hydroxyapatite(HAp) in structural and spectrophotometric characteristics was investigated to make clear the relation between the difference of optical properties by heat treatment and radical formation seemed to be caused by appearance of vacancy in apatitic structure and to grasp the characteristics of photoexcitation connected with photocatalytic behavior of HAp. The basic apatitic structure of the HAp sample scarcely varied often by heating up to 1150°C in air. The structural water left the lattice at 1150°C from the results of XRD and FTIR spectra. The coloring of the HAp sample occurred with heat treatment, especially, at 1150°C. The strong UV absorption under 400 nm was observed after heating at 1150°C. ESR signals appeared after heating at 900°C and 1150°C. The g-values of the ESR signals were assigned as O2− species, and it is assumed that the vacancy site move in the crystalline as well as TiO2. The strong oxidation would influence to the HAp sample with heating at 1150°C from the results that the phase of the signal of Mn2+ after heating at 1150°C was reverse compared with those at less than 900°C. 相似文献