共查询到20条相似文献,搜索用时 31 毫秒
1.
Rare-earth-doped polycrystalline Ca3(PO4)2:Eu, Ca3(PO4)2:Dy and Ca3(PO4)2:Eu,Dy phosphors prepared by a modified solid-state synthesis has been studied for its X-ray diffraction, thermoluminescence (TL) and photoluminescence (PL) characteristics. The PL emission spectra of the phosphor suggest the presence of Eu3+ ion in Ca3(PO4)2:Eu and Dy3+ ion in Ca3(PO4)2:Dy lattice sites. The TL glow curve of the Ca3(PO4)2:Eu compounds has a simple structure with a prominent peak at 228 °C, while Ca3(PO4)2:Dy peaking at 146 and 230 °C. TL sensitivity of phosphors are compared with CaSO4: Dy and found 1.52 and 1.20 times less in Ca3(PO4)2:Eu and Ca3(PO4)2:Dy phosphors, respectively. The Ca3(PO4)2:Eu,Dy phosphors shows switching behavior under two different excitation wavelengths and enhancement in PL intensity of Dy3+ ions were reported. The paper discusses the photoluminescence and thermoluminescence behavior of Eu3+ and Dy3+ ion in Ca3(PO4)2 hosts, it may be applicable to solid-state lighting as well as thermoluminescence dosimetry applications. 相似文献
2.
Mei Long Wei Li Haiyan Zhao Huixin Li Lingdong Sun Zhenggui Wei 《Journal of luminescence》2008,128(3):428-436
In this study, Eu3+-doped nanocrystalline Ca10(PO4)6(OH)2 (Ca10−xEux(PO4)6(OH)2) with different particle sizes have been prepared by the thermal decomposition of precursors. Size-dependent microstructure could be observed in nanocrystalline Ca10−xEux(PO4)6(OH)2. The lattices of Ca10−xEux(PO4)6(OH)2 nanocrystals were more distorted in comparison with the bulk, and the smaller the particle size, the more distorted the lattices. Room temperature photoluminescence showed europium site preference was also size-dependent, with the majority of Eu3+ ions occupying Ca(II) sites in the bulk, but more and more Eu3+ ions occupying Ca(I) sites in Ca10−xEux(PO4)6(OH)2 with decreasing particle size. Fluorescent properties of Ca10−xEux(PO4)6(OH)2 were considered to be influenced by both microstructure and site preference of Eu3+ ions. An abnormal strong intensity of 5D0-7F0 transition was observed in bulk and larger Ca10−xEux(PO4)6(OH)2 nanocrystals, but the relative intensities of 5D0-7F0 transition to 5D0-7F1,2,3,4 transition of Eu3+ became weaker as the particle sizes decreased. As the particle sizes became smaller, the ratios of the red emission transition (5D0-7F2) to the orange emission transition (5D0-7F1) (R/O values) first increased by comparing the bulk sample with 96 nm sample, and then decreased by comparing 96 nm sample to 57 nm sample. The quenching concentrations of Ca10−xEux(PO4)6(OH)2 samples increased with decreasing particle size. Possible mechanisms responsible for these phenomena were proposed. Since nanosized Ca10−xEux(PO4)6(OH)2 showed higher fluorescent intensities, higher R/O values and higher quenching concentrations, this material is considered to be a promising phosphor. 相似文献
3.
Multi-color long lasting phosphorescent (LLP) phenomenon in β-Zn3(PO4)2:Mn2+,Zr4+ was systematically investigated. It is found that the red (λEm=616 nm) LLP performance of Mn2+ such as brightness and duration is largely improved, and that the blue (λEm=475 nm) LLP of Zr4+ with lower intensity appears when Zr4+ ions are co-doped into the matrix. The fluorescence, phosphorescence and thermoluminescence (TL) spectra show that Mn2+ ion is solely expected as a luminescent center, while Zr4+ ion not only acts as a luminescent center, but also induces an electron trap (TrapZr) associated with a TL peak at 344 K. The trap depth for TrapZr is 0.25 eV, while that for the intrinsic trap is 0.38 eV, associated with a dominant peak at 385 K for Zn3(PO4)2:Mn2+. The Zr4+-induced trap with suitable depth is responsible for the improvement of the red LLP of Mn2+ ion and the appearance of the blue LLP of Zr4+ ion. The LLP mechanism is also investigated. 相似文献
4.
The H2 reduced NiFe2−xCrxO4 can be used to decompose CO2 to C repeatedly. A series of nanocrystalline Ni-ferrite doping different contents of Cr3+ were synthesized by mixed ions co-precipitation method and characterized by XRD, BET and TEM. The results showed that their crystallite sizes were 1-2 nm and BET surface area changed from 220 to 285 m2/g. The evaluation of the activity and stability indicated that Ni-ferrite with 4 wt% Cr3+ dopant could be used repeatedly as many as 60 times and was transformed to FeyNi1−y (0<y<1) alloy and Fe5C2 gradually during the cycle decomposition of CO2 to carbon, especially for no Cr3+ sample. After the 60th reaction, although NiFe2O4 phase just remained 2.1 wt%, the decomposition activity of Ni-ferrite with 4 wt% Cr3+ was still 60% of initial activity. This fact suggests that nanocrystalline FeyNi1−y (0<y<1) alloy from the cycle reaction can contribute to the decomposition of CO2. The results from scanning electron microscopy (SEM), TEM and XRD show that the deposited carbon from CO2 decomposition consisted of amorphous, crystallite and carbon nanotubes. 相似文献
5.
The photoluminescence properties of Y1−x(PO3)3:xEu3+ (0<x≤0.2) are investigated. The excitation spectrum of Y0.85(PO3)3:0.15Eu3+ shows that both the (PO3)33− groups and the CT bands of O2−-Y3+ can efficiently absorb the excitation energy in the region of 120-250 nm. Under 147 nm excitation, the optimal emissive intensity of Y1−x(PO3)3:xEu3+ (0<x≤0.2) is about 36% of the commercial phosphor (Y,Gd)BO3:Eu3+, which hints that the absorbed energy by the host matrix could be efficiently transferred to Eu3+. We try to study the concentration quenching mechanism of Y1−x(PO3)3:xEu3+ (0<x≤0.2) under 147 and 172 nm excitation. 相似文献
6.
I.M. Nagpure Shreyas S. PitaleE. Coetsee O.M. NtwaeaborwaJ.J. Terblans H.C. Swart 《Applied Surface Science》2011,257(23):10147-10155
Tb3+-doped Sr3(PO4)2 phosphor was prepared by a sol-gel combustion method. A trigonal structure having Sr and O atoms occupying two different lattice sites were obtained. Scanning Auger nanoprobe was used to analyze the morphology of the particles. Photoluminescence (PL) and cathodoluminescence (CL) properties of Sr3(PO4)2:Tb powder phosphors were evaluated and compared. In addition, the CL intensity degradation of Sr3(PO4)2:Tb was evaluated when the powders were irradiated with a beam of electrons in a vacuum chamber maintained at an O2 pressure of 1 × 10−6 Torr or a background pressure of 1 × 10−8 Torr O2. The surface chemical composition of the degraded powders, analyzed by X-ray photoelectron spectroscopy (XPS), suggests that new compounds (metal oxides) of strontium and phosphorous were formed on the surface. It is most likely that these compounds contributed to the CL intensity degradation of the Sr3(PO4)2:Tb phosphors. The CL properties and possible mechanism by which the new metal oxides were formed on the surface due to a prolonged electron beam irradiation are discussed. 相似文献
7.
Present study reports the structural, optical and dielectric properties of Ni substituted NdFe1−xNixO3 (0 ≤ x ≤ 0.5) compounds prepared through the ceramic method. X-ray diffraction (XRD) confirmed an orthorhombic crystal structure of all the samples. Both unit cell volume and grain size were found to decrease with an increase in Ni concentration. Morphological study by Scanning electron microscope (SEM) shows less porosity with Ni substitution in present system. From UV–vis spectroscopy, the optical band gap was found to increase with Ni doping. This observed behavior was explained on the basis of reduction in crystallite size, unit cell volume and its impact on the crystal field potential of the system after Ni substitution. The dielectric properties (?′ and tanδ) as a function of frequency or temperature, and the ac electrical conductivity (σac) as a function of frequency have been studied. Hopping of charge carriers between Fe2+ → Fe3+ ions and Ni2+ → Ni3+ ions are held responsible for both electrical and dielectric dispersion in the system. Wide optical band gap and a very high dielectric constant of these materials promote them to be a suitable candidate for memory based devices in electronic industry. 相似文献
8.
Electron spin resonance (ESR), thermoluminescence and photoluminescence studies in Eu2+ activated Sr5(PO4)3Cl phosphor are reported in this paper. The Sr5(PO4)3Cl:Eu2+ phosphor is twice as sensitive as the conventional CaSO4:Dy phosphor used in thermoluminescence dosimetry of ionizing radiations. It has a linear response, simple glow curve, emission peaking at 456 nm. The defect centers formed in the Sr5(PO4)3Cl:Eu2+phosphor are studied by using the technique of ESR. A dominant TL glow peak at 430 K with a smaller shoulder at 410 K is observed in the phosphor. ESR studies indicate the presence at three centers at room temperature. Step annealing measurements show a connection between one of the centers and the dominant glow peak at 430 K. The 430 K TL peak is well correlated with center I, which is tentatively identified as (PO4)2− radical. 相似文献
9.
He Kun Wang YanhangZu Chengkui Zhao HuifengLiu Yonghua Chen JiangHan Bin Ma Juanrong 《Physica B: Condensed Matter》2011,406(20):3947-3950
The crystallization mechanism and conductivity of lithium aluminum germanium phosphate [LAGP] glass-ceramics fabricated from Li1+xAlxGe2−x(PO4)3 (x=0.0-0.7) glass system were investigated as a function of Al2O3 additions. A non-isothermal analysis was performed to study the crystallization behavior of LAGP glass-ceramics at various heating rates (5-25K min−1) by the Kissinger equation and the Augis-Bennett equation, illustrating volume crystallization for the glass-ceramics. The crystal identification and microstructure in glass-ceramics containing various Al2O3 contents were analyzed by means of XRD and FESEM. The main phase of the glass-ceramics was found to be LiGe2(PO4)3, with AlPO4 as the impurity phase. Additionally the highest total ionic conductivity (5.8×10−4 S/cm) at room temperature was obtained when x=0.5 for Li1+xAlxGe2−x(PO4)3 (x=0.0-0.7) glass-ceramics, suggesting that it was a promising electrolyte for practical application in all-solid-state lithium batteries. 相似文献
10.
I.M. Nagpure Shreyas S. Pitale E. CoetseeO.M. Ntwaeaborwa J.J. TerblansH.C. Swart 《Physica B: Condensed Matter》2012,407(10):1505-1508
Eu activated Sr5(PO4)3F phosphor powders have been subjected to the electron bombardment at 2 keV (10 μA) at an oxygen pressure of 1×10−6 Torr. The synthesized Sr5(PO4)3F phosphor was identical to the hexagonal apatite structure, with the Sr present at two different sites Cs (S1) and C3 (S2) in the Sr5(PO4)3F host, as inferred from the crystallographic study. Cathodoluminescence (CL) and Auger electron spectroscopy of the phosphor excited by the same electron beam were used to monitor changes in the surface state during prolonged electron bombardment. A direct correlation between the surface reactions and the degradation of the CL brightness was observed. Both C and F were depleted from the surface during electron bombardment. The postulated mechanism for the electron stimulated chemical reactions on the phosphor surface is electron beam dissociation of molecular species to atomic species, which subsequently react with C to form volatile compounds CO2, CH4, etc. and with Sr5(PO4)3F to form a non luminescence layer of metal oxides of Sr and P. 相似文献
11.
Antiferromagnetic phase transition in two vanadium garnets AgCa2Co2V3O12 and AgCa2Ni2V3O12 has been found and investigated extensively. The heat capacity exhibits sharp peak due to the antiferromagnetic order with the Néel temperature TN=6.39 K for AgCa2Co2V3O12 and 7.21 K for AgCa2Ni2V3O12, respectively. The magnetic susceptibilities exhibit broad maximum, and these TN correspond to the inflection points of the magnetic susceptibility χ a little lower than T(χmax). The magnetic entropy changes from zero to 20 K per mol Co2+ and Ni2+ ions are 5.31 J K−1 mol-Co2+-ion−1 and 6.85 J K−1 mol-Ni2+-ion−1, indicating S=1/2 for Co2+ ion and S=1 for Ni2+ ion. The magnetic susceptibility of AgCa2Ni2V3O12 shows the Curie-Weiss behavior between 20 and 350 K with the effective magnetic moment μeff=3.23 μB Ni2+-ion−1 and the Weiss constant θ=−16.4 K (antiferromagnetic sign). Nevertheless, the simple Curie-Weiss law cannot be applicable for AgCa2Co2V3O12. The complex temperature dependence of magnetic susceptibility has been interpreted within the framework of Tanabe-Sugano energy diagram, which is analyzed on the basis of crystalline electric field. The ground state is the spin doublet state 2E(t26e) and the first excited state is spin quartet state 4T1(t25e2) which locates extremely close to the ground state. The low spin state S=1/2 for Co2+ ion is verified experimentally at least below 20 K which is in agreement with the result of the heat capacity. 相似文献
12.
The magnetic property of double doped manganite Nd0.5(1+x)Ca0.5(1−x)Mn(1−x)CrxO3 with a fixed ratio of Mn3+:Mn4+=1:1 has been investigated. For the undoped sample, it undergoes one transition from charge disordering to charge ordering (CO) associated with paramagnetic (PM)-antiferromagnetic (AFM) phase transition at T<250 K. The long range AFM ordering seems to form at 35 K, rather than previously reported 150 K. At low temperature, an asymmetrical M-H hysteresis loop occurs due to weak AFM coupling. For the doped samples, the substitution of Cr3+ for Mn3+ ions causes the increase of magnetization and the rise of Tc. As the Cr3+ concentration increases, the CO domain gradually becomes smaller and the CO melting process emerges. At low temperature, the FM superexchange interaction between Mn3+ and Cr3+ ions causes a magnetic upturn, namely, the second FM phase transition. 相似文献
13.
Magnetic materials such as NixZn(1−x)Fe2O4 have resonant frequency in high frequency; therefore, they are more useful especially in microwaves. The NixZn(1−x)Fe2O4 was prepared by the chemical coprecipitation method using citrate precursors, and the fritless thick film was screen printed on alumina substrates. The composition-dependent permeability and permittivity in the high frequency 8–12 GHz are investigated. Using the overlay technique on Ag-thick-film patch antenna, the change in reflectance and transmittance has been measured. The NixZn(1−x)Fe2O4 thick film, when used as overlay on Ag-thick-film patch antenna, changes the resonance characteristics. The changes in resonance frequency, reflectance and transmittance have been used to calculate the permeability and permittivity of the thick film. Zinc-concentration-dependent changes are obtained. 相似文献
14.
Gurinder Pal Singh Parvinder KaurSimranpreet Kaur D.P. Singh 《Physica B: Condensed Matter》2012,407(21):4269-4273
xV2O5–xCeO2–(30−x)PbO–(70−x) B2O3 glasses are synthesized by using the melt quench technique. The number of studies such as XRD, density, molar volume, optical band gap, refractive index and FTIR spectroscopy are employed to characterize the glasses. The band gap decreases from 2.20 to 1.78 eV and density increases from 3.49 to 4.25 g/cm3. FTIR spectroscopy reveals that incorporation of V2O5 in glass network helps to convert the structural units of [BO3] into [BO4]. At higher concentration of vanadium, VO vibration of [VO5] structural units and V–O–V vibration are present. The bond ionicity of glasses increases with incorporation of V2O5 contents. 相似文献
15.
Yong Joon Park Min Gyu KimYoung-Sik Hong Xianglan WuKwang Sun Ryu Soon Ho Chang 《Solid State Communications》2003,127(7):509-514
Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2 (X=0.17, 0.25, 0.33, 0.5) compounds are prepared by a simple combustion method. The Rietvelt analysis shows that these compounds could be classified as having the α-NaFeO2 structure. The initial charge-discharge and irreversible capacity increases with the decrease of x in Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2. Indeed, Li[Ni0.50Mn0.50]O2 compound shows relatively low initial discharge capacity of 200 mAh/g and large capacity loss during cycling, with Li[Ni0.17Li0.22Mn0.61]O2 and Li[Ni0.25Li0.17Mn0.58]O2 compounds exhibit high initial discharge capacity over 245 mAh/g and stable cycle performance in the voltage range of 4.8 -2.0 V. On the other hand, XANES analysis shows that the oxidation state of Ni ion reversibly changes between Ni2+ and about Ni3+, while the oxidation state of Mn ion sustains Mn4+ during charge-discharge process. This result does not agree with the previously reported ‘electrochemistry model’ of Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2, in which Ni ion changes between Ni2+ and NI4+. Based on these results, we modified oxidation-state change of Mn and Ni ion during charge-discharge process. 相似文献
16.
Øyvind Hatlevik 《Journal of Physics and Chemistry of Solids》2004,65(1):61-63
Oxidation of [CrII(NCMe)4][BF4]2 with thianthrinium tetrafluoroborate forms [CrIII(NCMe)6][BF4]3 exhibiting two νCN absorptions at 2331 and 2301 cm−1, and has been structurally characterized with an average Cr-N distance of 1.999 Å. From the electronic absorption spectra the ligand field splitting, Δ0, is 20,160 cm−1, which is slightly larger than [CrIII(OH2)6]3+ in accord with the divalent chromium analogues. The 298 K ESR has a resonance at g=1.9884, and the magnetic susceptibility has a 300 K moment of 3.85μB characteristic of S=3/2 Cr(III). The field dependence of the magnetization can be fit to the Brillouin function also characteristic of S=3/2. 相似文献
17.
Sang Soo Yu Kyung Hee Han Young Eon Ihm Dojin Kim Hyojin Kim Chang Soo Kim Hyun Ryu Sangjun Oh 《Journal of magnetism and magnetic materials》2006
Amorphous Ge1−xCrx thin films are deposited on (1 0 0)Si by using a thermal evaporator. Amorphous phase is obtained when Cr concentration is lower than 30.7 at%. The electrical resistivities are 1.89×10−3–0.96×102 Ω cm at 300 K, and decrease with Cr concentration. The Ge1−xCrx thin films are p-type. The hole concentrations are 5×1016–7×1021 cm−3 at 300 K, and increase with Cr concentration. Magnetizations are 7.60–1.57 emu/cm3 at 5 K in the applied field of 2 T. The magnetizations decrease with Cr concentration and temperature. Magnetization characteristics show that the Ge1−xCrx thin films are paramagnetic. 相似文献
18.
By using diamond anvil cell (DAC), high-pressure Raman spectroscopic studies of orthophosphates Ba3(PO4)2 and Sr3(PO4)2 were carried out up to 30.7 and 30.1 GPa, respectively. No pressure-induced phase transition was found in the studies. A methanol:ethanol:water (16:3:1) mixture was used as pressure medium in DAC, which is expected to exhibit nearly hydrostatic behavior up to about 14.4 GPa at room temperature. The behaviors of the phosphate modes in Ba3(PO4)2 and Sr3(PO4)2 below 14.4 GPa were quantitatively analyzed. The Raman shift of all modes increased linearly and continuously with pressure in Ba3(PO4)2 and Sr3(PO4)2. The pressure coefficients of the phosphate modes in Ba3(PO4)2 range from 2.8179 to 3.4186 cm−1 GPa−1 for ν3, 2.9609 cm−1 GPa−1 for ν1, from 0.9855 to 1.8085 cm−1 GPa−1 for ν4, and 1.4330 cm−1 GPa−1 for ν2, and the pressure coefficients of the phosphate modes in Sr3(PO4)2 range from 3.4247 to 4.3765 cm−1 GPa−1 for ν3, 3.7808 cm−1 GPa−1 for ν1, from 1.1005 to 1.9244 cm−1 GPa−1 for ν4, and 1.5647 cm−1 GPa−1 for ν2. 相似文献
19.
C.S. ZhangL. Yang 《Journal of magnetism and magnetic materials》2012,324(8):1469-1472
Core-shell Co(1−x)NixFe2O4/polyaniline nanoparticles, where the core was Co(1−x)NixFe2O4 and the shell was polyaniline, were prepared by the combination of sol-gel process and in-situ polymerization methods. Nanoparticles were investigated by Fourier transform spectrometer, X-ray diffraction diffractometer, Scanning electron microscope, Differential thermal analysis and Superconductor quantum interference device. The results showed that the saturation magnetization of pure Co(1−x)NixFe2O4 nanoparticles were 57.57 emu/g, but Co(1−x)NixFe2O4/polyaniline composites were 37.36 emu/g. It was attributed to the lower content (15 wt%), smaller size and their uneven distribution of Co(1−x)NixFe2O4 nanoparticles in the final microsphere composites. Both Co(1−x)NixFe2O4 and PANI/Co(1−x)NixFe2O4 showed superparamagnetism. 相似文献
20.
Optical transitions in normal-spinel Co3O4 have been identified by investigating the variation of its optical absorption spectrum with the replacement of Co by Zn. Three optical-transition structures were located at about 1.65, 2.4, and 2.8 eV from the measured dielectric function of Co3O4 by spectroscopic ellipsometry. The variation of the absorption structures with the Zn substitution (ZnxCo3−xO4) can be explained in terms of charge-transfer transitions involving d states of Co ions. The 1.65 eV structure is assigned to a d-d charge-transfer transition between the t2g states of octahedral Co3+ ion and t2 states of tetrahedral Co2+ ion, t2g(Co3+)→t2(Co2+). The 2.4 and 2.8 eV structures are interpreted as due to charge-transfer transitions involving the p states of O2− ion: p(O2−)→t2(Co2+) for the 2.4 eV absorption and p(O2−)→eg(Co3+) for the 2.8 eV absorption. The observed gradual reduction of the 1.65 and 2.4 eV absorption strength with the increase of the Zn composition for ZnxCo3−xO4 can be explained in terms of the substitution of the tetrahedral Co2+ sites by Zn2+ ions. The crystal-field splitting ΔOh between the eg and the t2g states of the octahedral Co3+ ion is estimated to be 2 eV. 相似文献