首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
In this paper, a series of Na3Ca6(1−x)(PO4)5:xEu2+ (NCP:xEu2+, 0  x  4%) phosphors were prepared by conventional solid-state reaction method, and their photoluminescence properties were studied. Upon 365 nm excitation, the typical NCP:2%Eu2+ phosphor shows an asymmetric bluish green emission band with the dominant peak at 498 nm which could be attributed to the 4f65d1-4f7 transition of Eu2+. By measuring the time-resolved photoluminescence spectra, it reveals more than one Eu2+ emission center in the Eu2+-activated NCP phosphors. By monitoring 498 nm, the excitation spectrum of NCP:2%Eu2+ demonstrates a broad excitation band ranging from 240 to 450 nm, which can match well with the emission wavelength of the NUV LED chip. The SEM image shows that the average particle size of NCP:2%Eu2+ is about 19.4 µm. The above results imply that the NCP:Eu2+ phosphor could have potential application in LEDs.  相似文献   

2.
Ca (or Sr)TiO3:Eu3+, M (Li+ or Na+ or K+) and CaTiO3:Pr3+, M (Li+ or Na+ or Ag+ or K+ or Gd3+ or La3+) powders were prepared by combustion synthesis method and the samples were further heated to ~1000 °C to improve the crystallinity. The structure and morphology of materials were examined by X-ray diffraction (XRD) and a scanning electron microscopy (SEM). The morphologies of SrTiO3:Eu3+, CaTiO3:Eu3+ or CaTiO3:Pr3+ powders co-doped with other metal ions were very similar. Small and coagulated particles of nearly cubical shapes with small size distribution having smooth and regular surface were formed. Photo-luminescence spectra of CaTiO3:Pr3+ and co-doped either with Li+, Na+, K+, Ag+, La3+ or Gd3+ ions showed red emissions at 613 nm due to the 1D2  3H4 transition of Pr3+. The variation of intensity of emission peak with different co-doping follows the order: K+ > Ag+ > Na+ > Li+ > La3+ > Gd3+. The characteristic emissions of CaTiO3:Eu3+ lattices had strong emission at 614 and 620 nm for 5D0  7F2 with other weak transitions observed at 580, 592, 654, 705 nm for 5D0  7Fn transitions where n = 0, 1, 3, 4 respectively in all host lattices. Photoluminescence intensity in SrTiO3:Eu3+ is more than CaTiO3:Eu3+ lattices. A remarkable increase of photoluminescence intensity (in 5D0  7F2 transition) was observed if co-doped with Li+ ions in CaTiO3:Eu3+ and SrTiO3:Eu3+.  相似文献   

3.
《Displays》2014,35(5):273-278
Three kinds of lanthanide phosphors (LaxLu1xF3: Eu3+, LaF3–CaF2:Eu3+ and LaF3: Eu3+) have been successfully synthesized based on three different ways such as molten salts, co-precipitation, supersonic and microwave irradiations. The as-prepared powder materials all exhibited red luminescence. Their crystal structures or morphologies were studied by means of X-ray powder diffraction and scanning electronic microscope. Eu3+-doped LaF3–CaF2 phosphor can be emissive under excitation at longer wavelengths (466 and 533 nm) excitations. Supersonic and microwave irradiations have shortened the reaction time of LaF3: Eu3+ crystals in 40 min under very low temperature (50 °C).  相似文献   

4.
In this study, Eu3+ doped Ca(WO4)1?x(MoO4)x phosphors were synthesized via high temperature solid-state reaction. Compared with the Eu3+ activated CaWO4 sample, an increment of MoO3 doping concentration could improve the emission intensity. Improved red afterglow originating from the 5D0 to 7FJ (J = 0, 1, 2, 3, 4) transitions of Eu3+ was observed after appropriate amount of MoO3 was added, and the optimal MoO3 doping concentration was experimentally determined to be 0.02. The proposed explanation for the afterglow property was also discussed.  相似文献   

5.
Phosphate glasses with chemical compositions of 74.5NaH2PO4–20ZnO–5Li2O–0.5Sm2O3 and 74NaH2PO4–20ZnO–5Li2O–0.5Sm2O3–0.5Eu2O3 were synthetized by melt quenching method. We investigated the influence of Sm3+/Eu3+ doping on the optical properties of phosphate glasses. X-ray Diffraction indicates that the samples have an amorphous structure. DSC measurements show a good thermal stability of phosphate glasses. Using the absorption spectra, Judd–Ofelt analysis was applied to absorption bands of Sm3+ (4f5) to carry out the three phenomenological parameters of Judd–Ofelt (JO). According to the obtained values of Ω2, Ω4 and Ω6, some radiative properties were theoretically determined. We report both the photoluminescence (PL) and the PL lifetime measurements of a prominent emission transition 4G5/2  6H5/2 (604 nm) of Sm3+ both in absence and in presence of Eu3+. It is shown that Eu3+ ions act as sensitizers for Sm3+ ions and contribute largely to the improvement of the radiative properties of phosphate glasses. An improvement of the PL lifetime value after adding Eu3+ ions (4.58 ms) is reported. The predicted lifetime (τrad) calculated by Judd–Ofelt theory and the experimental lifetime (τmeas) for the prepared phosphate glasses were compared with those of other works. Photoluminescence (PL) intensity of 4G5/2  6H5/2 (604 nm), 4G5/2  6H7/2 (567 nm), 4G5/2  6H9/2 (650 nm) and 4G5/2  6H11/2 (706 nm) and the quantum efficiency (η) for the excited 4G5/2 level were enhanced after adding Eu3+. The radiative properties obtained for (Sm, Eu) codoped phosphate glasses suggest that the present material can be a potential candidate for the development of color display devices.  相似文献   

6.
A series of Eu3+-activated Li2Mg2(WO4)3 (LMW) materials were synthesized by high temperature solid state reactions. The phosphor can be effectively excited by 394 nm near ultraviolet light and emit intense red light with high color purity. Prepared phosphors can be indexed to LMW with particular lyonsite structure. The occupation of Eu3+ in LMW is selective. Most of Eu3+ comes into 1A sites without inversion symmetry. The present research suggests that LMW is a suitable host for luminescence applications and Eu3+-activated LMW is a promising phosphor for phosphor-converted white light-emitting diodes.  相似文献   

7.
This work explores the synthesis of nanocrystalline MgO:Cr3+ (1–9 mol%) nanophosphors via solution combustion route at 400 °C. The nanophosphors were well characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infra-Red (FTIR) spectroscopy. PXRD results confirm cubic phase and SEM micrographs indicate that the particles are highly porous and agglomerated. The TEM images show that the powder consists of spherical particles of size ∼5–15 nm. Upon 356 nm excitation the emission profile of MgO:Cr3+ exhibits an emission peak at 677 nm due to 2Eg  4A2g transition. It was observed that PL intensity increases with increase in Cr3+ concentration and highest PL intensity was observed for 3 mol% doped sample and afterward it decreases, attributed to concentration quenching. The resultant CIE chromaticity co-ordinates in the white region make the present phosphor highly useful for display applications and also for white light-emitting diodes (WLEDs).  相似文献   

8.
Near-ultraviolet (NUV)-excitable phosphors composed of Ba8.9-(1/2)pNapEu0.1Y2Si6O24 (p = 0–0.8) and Ba8.7-qNa0.4Eu0.1MnqY2Si6O24 (q = 0–0.4) were prepared via a solid-state reaction in a reducing atmosphere. The X-ray diffraction patterns of the obtained phosphors were examined to index the peak positions. After Na+ substitution for Ba2+ in the Ba8.9Eu0.1Y2Si6O24 host lattice, the clear shift from green to yellow emission was observed. The Gaussian components of Ba8.9-(1/2)pNapEu0.1Y2Si6O24 (p = 0, 0.4, and 0.8) phosphors were exploited by using the three different Eu2+ ion sites in the host lattice. The dependence of the luminescent intensity of the Mn2+ co-doped (q = 0–0.4) host lattices on the fixed Na+ and Eu2+ contents was also investigated. Co-doping Na+ with Mn2+ and Eu2+ emitters in the host structure enabled efficient energy transfer from Eu2+ to Mn2+. The mechanism underlying this energy transfer was also discussed. The Commission Internationale de I’Eclairage (CIE) coordinates near the yellow and red regions of the obtained phosphors were observed. Each of Ba8.9Eu0.1Y2Si6O24, Ba8.7Na0.4Eu0.1Y2Si6O24, and Ba8.6Na0.4Eu0.1Mn0.1Y2Si6O24 phosphors with a 405 nm LED chip was fabricated. The color rendering index (CRI, Ra) at correlated color temperature (CCT) with the CIE coordinates was exhibited for the LEDs. The thermal quenching and activation energy for the Ba8.7Na0.4Eu0.1Y2Si6O24 and Ba8.6Na0.4Eu0.1Mn0.1Y2Si6O24 phosphors were measured.  相似文献   

9.
CaMoO4:RE3+,Yb3+ (RE = Er, Ho, Tm) phosphors were successfully synthesized by a facile hydrothermal method. XRD patterns confirmed tetragonal structure under different RE3+ and M+ ions doping conditions. Particles shapes and sizes were confirmed by SEM and TEM analyses. Particles shape and size were well tuned by control of solution pH; spherical balls consisting of nano-grains at low pH of ∼2, rice grain shapes at moderate pH of ∼6, and thin flakes at higher pH of ∼12, were observed. Fine tunability of upconversion (UC) emission color was achieved by doping multiple RE3+ ions within a single CaMoO4 host. Blue, green and orange upconverted emission were observed by doping Tm3+, Er3+ and Ho3+ in the CaMoO4, respectively. Further, the emission colors were well tuned by the combination of Tm, Er and Ho ions and their concentrations. CaMoO4:Tm3+,Ho3+,Yb3+ exhibited perfect white emission with well tunability from cool white to warm white colors. Substitution of part of Ca ions by M+ (M = Li, Na, K, Rb) ions affected the crystal field symmetry around RE3+ ions and hence changed the transition probabilities between their f–f transition levels, consequently intensified the UC intensities. The blue (Tm3+), green (Er3+), and orange (Ho3+) upconversion intensities of CaMoO4:RE3+,Yb3+,0.10 K+ phosphors increased by 60, 50 and 40 folds compared to the unsubstituted analogues, respectively. The K substituted CaMoO4:RE3+,Yb3+,K+ phosphors exhibited intense UC emissions visible by naked eye even pumped by less than 1 mW laser power and can have potential application in displays and variety of other applications.  相似文献   

10.
Ab initio calculations have been performed to study the influence of hybridization, substitution, and cooperativity on the tetrel bond in the complexes of PySiX3 (Py = pyridine and X = halogen). The tetrel bond becomes stronger in the order of p-PySiF3⋯NCH(sp) < p-PySiF3⋯NHCH2(sp2) < p-PySiF3⋯NH3(sp3). The electron-donating group in the electron donor strengthens the tetrel bond, and this effect is mainly achieved through electrostatic and polarization interactions. Tetrel bonding displays cooperative effects with triel bonding and chalcogen bonding, characterized by shorter binding distances and greater electron densities. The cooperative effects between triel/chalcogen bond and tetrel bond have been analyzed by molecular electrostatic potentials and charge transfer. Energy decomposition indicates that many-body effects are mainly caused by polarization energy. The geometries of Si⋯N interaction and its applications in crystal materials have been characterized and evidenced by a CSD research.  相似文献   

11.
A novel vanadium oxide polypropylene carbonate modified glassy carbon electrode was developed and used for the measurement of ascorbic acid (AA). The electrode was prepared by casting a mixture of vanadium tri(isopropoxide) oxide (VO(OC3H7)3) and poly(propylene carbonate) (PPC) onto the surface of a glassy carbon electrode. The electrochemical behavior of the VO(OC3H7)3–PPC film modified glassy carbon electrode was investigated by cyclic voltammetry and amperometry. This modified electrode exhibited electrocatalytic response to the oxidation of ascorbic acid. Compared with a bare glassy carbon electrode, the modified electrode exhibits a 220 mV shift of the oxidation potential of ascorbic acid in the cathodic direction and a marked enhancement of the current response. The response current revealed a good linear relationship with the concentration of ascorbic acid in the range of 4 × 10−8 and 1 × 10−4 mol L−1 and the detection limit of 1.5 × 10−8 mol L−1 (S/N = 3) in the pH 8.06 Britton–Robinson solution. Quantitative recovery of the ascorbic acid in synthetic samples has been obtained and the interferences from different species have been studied. The method has been successfully applied to the determination of ascorbic acid in fruits. The concentrations of ascorbic acid measured by this method are in good agreement with the literature value. It is much promising for the modified films to be used as an electrochemical sensor for the detection of ascorbic acid.  相似文献   

12.
This article aims at finding efficient hyperspectral indices for the estimation of forest sun leaf chlorophyll content (CHL, µg cmleaf? 2), sun leaf mass per area (LMA, gdry matter mleaf? 2), canopy leaf area index (LAI, m2leaf msoil? 2) and leaf canopy biomass (Bleaf, gdry matter msoil? 2). These parameters are useful inputs for forest ecosystem simulations at landscape scale. The method is based on the determination of the best vegetation indices (index form and wavelengths) using the radiative transfer model PROSAIL (formed by the newly-calibrated leaf reflectance model PROSPECT coupled with the multi-layer version of the canopy radiative transfer model SAIL). The results are tested on experimental measurements at both leaf and canopy scales. At the leaf scale, it is possible to estimate CHL with high precision using a two wavelength vegetation index after a simulation based calibration. At the leaf scale, the LMA is more difficult to estimate with indices. At the canopy scale, efficient indices were determined on a generic simulated database to estimate CHL, LMA, LAI and Bleaf in a general way. These indices were then applied to two Hyperion images (50 plots) on the Fontainebleau and Fougères forests and portable spectroradiometer measurements. They showed good results with an RMSE of 8.2 µg cm? 2 for CHL, 9.1 g m? 2 for LMA, 1.7 m2 m? 2 for LAI and 50.6 g m? 2 for Bleaf. However, at the canopy scale, even if the wavelengths of the calibrated indices were accurately determined with the simulated database, the regressions between the indices and the biophysical characteristics still had to be calibrated on measurements. At the canopy scale, the best indices were: for leaf chlorophyll content: NDchl = (ρ925 ? ρ710)/(ρ925 + ρ710), for leaf mass per area: NDLMA = (ρ2260 ? ρ1490)/(ρ2260 + ρ1490), for leaf area index: DLAI = ρ1725 ? ρ970, and for canopy leaf biomass: NDBleaf = (ρ2160 ? ρ1540)/(ρ2160 + ρ1540).  相似文献   

13.
《Displays》2014,35(5):279-286
Dysprosium doped di-strontium magnesium di-silicate namely Sr2MgSi2O7:Dy3+ phosphor was prepared by the solid state reaction method. The phase structure, surface morphology, particle size, elemental analysis was analyzed by using XRD, TEM, EDX and FTIR techniques. The EDX and FTIR spectra confirm the present elements in Sr2MgSi2O7:Dy3+ phosphor. The optical properties of Sr2MgSi2O7:Dy3+ phosphor was investigated utilizing thermoluminescence (TL), photoluminescence (PL), long lasting phosphorescence and mechanoluminescence (ML). Under the ultraviolet excitation, the emission spectra of Sr2MgSi2O7:Dy3+ phosphor are composed of a broad band and the characteristic emission of Dy3+ peaking at 470 nm (blue), 575 nm (yellow) and 678 nm (red), originating from the transitions of 4F9/2  6H15/2, 4F9/2  6H13/2 and 4F9/2  6H11/2. CIE color coordinates of Sr2MgSi2O7:Dy3+ are suitable as white light emitting phosphor. Decay graph indicate that this phosphor also contains fast decay and slow decay process. The peak of ML intensity increases linearly with increasing impact velocity of the moving piston. The possible mechanism of this white light emitting long lasting phosphor is also investigated.  相似文献   

14.
Ce3+–Mn2+–Tb3+ cooperative barium–yttrium-orthosilicate phosphors composed of Ba9-3m/2-n-3p/2CemMnnTbpY2Si6O24 (m = 0.005–0.4, n = 0–0.5, p = 0–0.5) were prepared using a solid-state reaction. The X-ray diffraction patterns of the resultant phosphors were examined to index the peak positions. The photoluminescence (PL) excitation and emission spectra of the Ce3+–Mn2+–Tb3+ activated phosphors were clearly monitored. The dependence of the luminescent intensity of the Mn2+–Tb3+ co-doped Ba9-3m/2CemY2Si6O24 host lattices on Ce3+ content (m = 0.025, 0.1) was also investigated. Co-doping Mn2+ into the Ce3+–Tb3+ co-doped host structure enabled energy transfer from Ce3+ to Mn2+; this energy transfer mechanism is discussed. The phosphors of Ce3+–Mn2+–Tb3+ doped Ba9Y2Si6O24 host lattice were prepared for efficient white-light emission under NUV excitation. With these phosphors, the desired CIE values including white region of the emission spectra were achieved.  相似文献   

15.
A polynomial P(X)  = Xd + ad  1Xd  1 + ⋯ is called lacunary when ad  1 =  0. We give bounds for the roots of such polynomials with complex coefficients. These bounds are much smaller than for general polynomials.  相似文献   

16.
The lowest-energy structures and stabilities of the heterodinuclear clusters, CNLin (n = 1–10) and relevant CNLin+ (n = 1–10) cations, are studied using the density functional theory with the 6-311 + G(3df) basis set. The CNLi6 and CNLi5+ clusters are the first three-dimensional ones in the CNLin0/+ series, respectively, and the CN group always caps the Lin0/+ moiety in the CNLin0/+ (n = 1–9) configurations. The CN triple bond is found to be completely cleaved in the CNLi100/+ clusters where the C and N atoms are bridged by two Li atoms. The CNLin (n = 2–10) clusters are hyperlithiated molecules with delocalized valence electrons and consequently possess low VIP values of 3.780–5.674 eV. Especially, the CNLi8 and CNLi10 molecules exhibit lower VIPs than that of Cs atom and can be regarded as heterobinuclear superalkali species. Furthermore, these two superalkali clusters show extraordinarily large first hyperpolarizabilities of 19,423 and 42,658 au, respectively. For the CNLin+ cationic species, the evolution of the energetic and electronic properties with the cluster size shows a special stability for CNLi2+.  相似文献   

17.
18.
Detection of hazardous chemical species by changing the electrical conductivity of a semiconductor matter is a proposed and applied way for decreasing their subsequent unpleasant effects. Recently, many examples of using inorganic or organic materials, polymeric, and also nano-sized species as sensors were reported in which, in some cases, those matters were strongly affective and suitable.In this project, we have made an assessment on whether the graphene segment or C20 fullerene, able to sense the existence of cyanogen chloride NCCl? In order to gain trustable results, the possible reaction pathways along with the adsorption kinetics were investigated. Moreover, the electronic density of states DOS showed that C20 fullerene senses the existence of cyanogen chloride agent with a clearer signal (ΔEg = 0.0110 eV) compared to the graphene segment (ΔEg = 0.0001 eV). Also the adsorption energy calculations showed that cyanogen chloride could be adsorbed by the fullerene in a multi-step process (Eads1 = −0.852 kcal mol−1; Eads2 = −0.446 kcal mol−1; Eads3 = −2.330 kcal mol−1).  相似文献   

19.
In order to reduce the response time of resistive oxygen sensors using porous cerium oxide thick film, it is important to ascertain the factors controlling response. Pressure modulation method (PMM) was used to find the rate-limiting step of sensor response. This useful method measures the amplitude of sensor output (H(f)) for the sine wave modulation of oxygen partial pressure at constant frequency (f). In PMM, “break” response time, which is minimum period in which the sensor responds precisely, can be measured. Three points were examined: (1) simulated calculations of PMM were carried out using a model of porous thick film in which spherical particles are connected in a three-dimensional network; (2) sensor response speed was experimentally measured using PMM; and (3) the diffusion coefficient and surface reaction coefficient were estimated by comparison between experiment and calculation. The plot of log f versus log H(f) in the high f region was found to have a slope of approximately −0.5 for both porous thick film and non-porous thin film, when the rate-limiting step was diffusion. Calculations showed the response time of porous thick film was 1/20 that of non-porous thin film when the grain diameter of the porous thick film was the same as the thickness of non-porous thin film. At 973 K, “break” response time (tb) of the resistive oxygen sensor was found by experiment to be 109 ms. It was concluded that the response of the resistive oxygen sensor prepared in this study was strongly controlled by diffusion at 923–1023 K, since the experiment revealed that the slope of plot of log f versus log H(f) in the high f region was approximately −0.5. At 923–1023 K, the diffusion coefficient of oxygen vacancy in porous ceria (DV) was expressed as follows: DV (m2s−1) = 5.78 × 10−4 exp(−1.94 eV/kT). At 1023 K, the surface reaction coefficient (K) was found to exceed 10−4 m/s.  相似文献   

20.
In this paper, we introduce “approximate solutions" to solve the following problem: given a polynomial F(x, y) over Q, where x represents an n -tuple of variables, can we find all the polynomials G(x) such that F(x, G(x)) is identically equal to a constant c in Q ? We have the following: let F(x, y) be a polynomial over Q and the degree of y in F(x, y) be n. Either there is a unique polynomial g(x)   Q [ x ], with its constant term equal to 0, such that F(x, y)  = j = 0ncj(y  g(x))jfor some rational numbers cj, hence, F(x, g(x)  + a)   Q for all a  Q, or there are at most t distinct polynomials g1(x),⋯ , gt(x), t  n, such that F(x, gi(x))   Q for 1   i  t. Suppose that F(x, y) is a polynomial of two variables. The polynomial g(x) for the first case, or g1(x),⋯ , gt(x) for the second case, are approximate solutions of F(x, y), respectively. There is also a polynomial time algorithm to find all of these approximate solutions. We then use Kronecker’s substitution to solve the case of F(x, y).  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号