Memory effect and cathodoluminescent properties of YAG:Nd<Superscript>3+</Superscript> nanoceramics

The cathodoluminescent properties of nanoceramics based on neodymium-doped yttrium–aluminum garnet (YAG:Nd³⁺) are studied in a wide optical spectral range (from UV to IR). It is shown that the spectral positions of the emission bands of nanoceramics are identical to that of single crystal, but the bands of nanoceramics are broadened by no more than 15% from the half bandwidths of single crystal. The intensity of cathodoluminescence bands in nanoceramics is lower, and the lifetimes of radiative levels are shorter. It is found for the first time that electron-beam irradiation of nanoceramics increases the cathodoluminescence intensity of bands in visible and UV ranges (by two or more times). Preliminary electron beam irradiation of YAG:Nd³⁺ nanoceramics samples leads to the increase of cathodoluminescence efficiency. Such effect retains for a long time (a year and more) and can be compared to the memory effect. This effect is not observed in single crystal. We propose a model describing this effect in nanoceramics.     

Synthesis and study of the luminescent properties of europium-doped yttrium niobate

A method of synthesis of single-phase europium-doped yttrium niobate powders without using additional fluxes is developed. Using this method, a series of samples with different europium concentrations are synthesized. The phase composition, grain size, and luminescent properties of the synthesized powders are studied. The optimal dopant concentration corresponding to the maximum luminescence intensity is determined. It is shown that the decay time of the most intense luminescence line of europium decreases with increasing europium concentration. Comparative analysis of the luminescent properties of calcium tungstate and the luminescent properties of a synthesized sample with the highest luminescence intensity is performed.     

Eu（Sm）－DBM－CPB体系的激光感生时间分辨荧光光谱的研究

用自装的激光感生时间分辨荧光光谱装置，研究了Ｅｕ、Ｓｉｎ－二苯甲酰甲烷（ＤＢＭ）体系在阳离子表面活性剂溴代十六烷基吡啶（ＣＰＢ）存在下的光谱特性和荧光衰减动力学特性。给出同时测定Ｅｕ和Ｓｉｎ的激光感生时间分辨荧光光谱分析方法，用于高纯氧化物中痕量Ｅｕ和Ｓｉｎ的测定，获得了满意的结果。     

Luminescence investigations of cubic boron nitride doped with beryllium

The cathodoluminescence and photoluminescence spectra of cubic boron nitride doped with beryllium under high-pressure and high-temperature conditions are investigated. It is revealed that, upon doping of cubic boron nitride with beryllium, the cathodoluminescence spectra exhibit a broad stable band. An increase in the impurity content leads to a shift in the position of the maximum of this band toward the short-wavelength range from ～315 to ～250 nm and to a change in the crystal color from dark yellow to blue. The structure, the intensity, and the position of the band at the maximum are studied as a function of the temperature of the cathodoluminescence measurement. The nature of the band is tentatively interpreted in the framework of the model of recombination at defects of the donor and acceptor types. It is assumed that several overlapping subbands which are associated with differently charged acceptor levels of beryllium are located in the vicinity of the valence band in the electronic structure of the doped cubic boron nitride. It is found that the photoluminescence spectra of single crystals of the doped cubic boron nitride contain three previously unknown zero-phonon lines at energies of 2.135, 2.270, and 2.600 eV.     

Pulsed cathodoluminescence of yttrium-aluminum garnet in the visible spectral range

The spectra of the pulsed cathodoluminescence of yttrium-aluminum garnet (YAG) laser crystals activated with various impurities (YAG:Nd; YAG:Nd,Ce; YAG:Cr; YAG:Cr,Ce; YAG:Er; and YAG:Sm) are studied. The bands of the rare-earth ions in the visible spectral range are identified. Luminescence of Ce²⁺ ion is revealed in the YAG:Cr,Ce crystal. Original Text ? Astro, Ltd., 2006.     

Conductivity-dependent cathodoluminescence in BaTiO3, SrTiO3 and TiO2

It is reported that similar cathodoluminescence spectra are excited by an electron beam striking BaTiO₃, SrTiO₃ and TiO₂ ceramics at room temperature. The energy location of the luminescence bands does not depend on various doping or reduction treatments. The luminescence intensity increases with the electron beam current as well as with the conduction electron density. The luminescence is interpreted as a fundamental transition of local character in the TiO₆ octahedron; the conduction electrons localized at the Ti sites in polaron states recombine with the 0–2p valence electron defects. The shape and energy location of the luminescence spectra are qualitatively in accordance with an explanation in terms of a configuration coordinate model.     

Rapid detection of doxycycline content in duck meat by using silver nanoparticles and alkylphenols polyoxyethylene enhanced fluorescence of europium complex

Doxycycline can coordinate with europium (III) to form europium (III)-doxycycline complex, which can emit the fluorescence characteristic peak of europium (III) at 617 nm in alkaline solution, and the experiment proved that the fluorescence intensity could be further enhanced in the presence of silver nanoparticles and surfactant alkylphenols polyoxyethylene. So this method was applied to detect doxycycline content in duck meat in this research. First, 390 and 617 nm were selected as the optimum excitation wavelength and optimum emission wavelength by three-dimensional fluorescence spectrometry, respectively. Second, the experimental conditions were optimized through single factor experiment. Lastly, the samples of doxycycline concentration range of 0.05–12 mg/L were analyzed under the optimum experimental conditions. A good linear relationship between the doxycycline concentration and the fluorescence intensity was obtained, and the determination coefficient and the root mean squared error of prediction were 0.9982 and 0.4363 mg/L, respectively. This research showed that it was feasible to achieve the rapid detection of doxycycline content in duck meat by using silver nanoparticles and alkylphenols polyoxyethylene enhanced the fluorescence of europium complex.     

Effect of X-Ray Radiation on the Valence State of Europium in Y2O3:Eu3+ Phosphor

Physics of the Solid State - The effect of X-ray radiation on the valence state of europium ions in the Y2O3 matrix was studied by EPR. The alternation of the charge of europium ions (Eu3+ →...     

Cathodoluminescence of large-area PLD grown ZnO thin films measured in transmission and reflection

Epitaxial ZnO thin films on sapphire substrates can be used as fast and laterally homogeneous scintillators to convert electrons into photons, for example for imaging purpose. We report on the improvement of the cathodoluminescence intensity of epitaxial pulsed laser deposited ZnO films on a-plane sapphire substrates with diameter up to 33 mm. The lateral homogeneity of the integral cathodoluminescence intensity was inspected using a modified RHEED setup. Cathodoluminescence spectra were excited at the ZnO side of the samples and detected both in reflection and in transmission geometry. The redshift of the excitonic cathodoluminescence peak in transmission relative to reflection and the peak shift with the excitation depth can be explained by a model based on self absorption of the photons in the ZnO film. PACS 78.60.Hk; 78.20.Bh; 81.05.Dz; 81.15.Fg     

Cathodoluminescence of radiative centers in wide-bandgap materials

Features of the local cathodoluminescence method during the investigation of wide-bandgap materials doped by rare earth ions are considered. The high energy of the primary electron beam, the possibility of variation of the specific excitation power by orders of magnitude, and the locality of the method allow one to study transitions, which require radiation with an energy of more than 5 eV to be excited, to study homogeneity of the dopant distribution with a spatial resolution better than 1 μm, and to investigate spectra of radiation emitted from various depths by a nondestructive technique. A model is proposed that allows one to evaluate the efficiency of radiative level excitation and the content of luminescent centers. We suggest a new approach to the investigation of electronic traps in wide-bandgap samples using variation of radiation intensity under stationary exposure.     

Cathodoluminescence of laser-annealed erbium-implanted zinc selenide

After zinc selenide crystals implanted with erbium ions had been annealed with a continuous wave (cw) krypton ion laser it was found that the cathodoluminescence emission intensity of the implanted erbium ions had been considerably enhanced. In order to gain some understanding of the physical processes involved in such an enhancement a comparison was made between thermal annealing and laser annealing of the implanted crystals. Clear differences were found in the cathodoluminescence spectra of the thermally annealed and laser-annealed samples. The increase in cathodoluminescence emission intensity produced by laser annealing was attributed to the production of selenium vacancies in the vicinity of the implanted erbium ions and leads us to suggest the possibility of site selective annealing by this technique.     

Selected properties of EuCo2(Si1−xGex)2 alloys

EuCo₂(Si_1−xGe_x)₂, x=0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 samples were synthesised by induction melting followed by annealing at 900 °C and rapid quenching. X-ray powder diffraction and Auger electron spectroscopy studies revealed that solid solutions are formed only for x?0.2 and x?0.7. Magnetic susceptibility investigations for the solid solutions revealed a dominant divalent europium valence state in the germanium-rich samples and a dominant trivalent europium component in the silicon-rich samples. In the germanium-rich samples, a long-range antiferromagnetic ordering was observed. In all samples studied, additional magnetic transitions at various temperatures were detected, which could be attributed to small clusters containing different europium chemical surrounding from that in the predominant phase.     

Measurements of plasma temperature and electron density in laser-induced copper plasma by time-resolved spectroscopy of neutral atom and ion emissions

Plasma produced by a 355 nm pulsed Nd:YAG laser with a pulse duration of 6 ns focussed onto a copper solid sample in air at atmospheric pressure is studied spectroscopically. The temperature and electron density characterizing the plasma are measured by time-resolved spectroscopy of neutral atom and ion line emissions in the time window of 300–2000 ns. An echelle spectrograph coupled with a gated intensified charge coupled detector is used to record the plasma emissions. The temperature is obtained using the Boltzmann plot method and the electron density is determined using the Saha-Boltzmann equation method. Both parameters are studied as a function of delay time with respect to the onset of the laser pulse. The results are discussed. The time window where the plasma is optically thin and is also in local thermodynamic equilibrium (LTE), necessary for the laser-induced breakdown spectroscopy (LIBS) analysis of samples, is deduced from the temporal evolution of the intensity ratio of two Cu I lines. It is found to be 700–1000 ns.     

Luminescence study of alumina nanopowders prepared by various methods

Mixed nanopowders of transition alumina prepared by combustion synthesis and phase pure ultra-porous α-alumina by oxidation method were investigated using low temperature time-resolved cathodoluminescence and photoluminescence spectroscopy under VUV-XUV excitation. In all samples along with the 7.6 eV emission of self-trapped excitons of α-alumina, luminescence bands due to F, F⁺ centres with maxima at 3 and 3.8 eV and other UV–visible luminescence bands of intrinsic and extrinsic origin with varying intensity depending on sample preparation method and thermal treatment were studied. In alumina nanopowders the excitonic excitation peak at ∼9.1 eV near fundamental absorption edge is shifted to the higher energies by 0.15 eV in comparison with the same feature in single crystals. The nanostructure of alumina is responsible for this shift.     

Studies of minority carrier transport in ZnO

The temperature dependence of the minority carrier diffusion length and lifetime in bulk n-type ZnO was studied using Electron-Beam-Induced Current (EBIC) and cathodoluminescence (CL) techniques. The diffusion length was observed to increase exponentially over the temperature range from 25 to 125 C, yielding an activation energy of 45 ± 2 meV. A concomitant decrease of the cathodoluminescence intensity for the near-band-edge transition was also observed. The activation energy determined by optical measurements was 58 ± 7 meV. The larger minority carrier diffusion length and smaller luminescence intensity are attributed to the increased lifetime of non-equilibrium holes in the valence band at elevated temperatures. Carrier trapping on Li-related levels with activation energy 283 ± 9 meV is also addressed.     

协同发光效应及机理探讨

在研究共存离子对稀土配合物荧光强度影响时发现,许多稀土和非稀土离子在一定浓度范围内可对配合物的荧光产生增强效应.这种现象与协同萃取类似,我们将其命名为“协同发光效应”.本文采用激光诱导荧光光谱法,研究了十四种稀土离子对Eu、Sm-TTA-Phen-Triton X-100体系和Eu、Sm-DBM-CPB体系的协同发光效应.并从稀土离子的化学性质,光谱能级和所形成配合物的化学结构和空间结构等方面综合考虑,提出协同发光机理.拟定出用于痕量铕和钐测定的薪的超高灵敏度分析方法.     

用阴极发光显微术研究YAG:Nd~(3+)晶体中的缺陷

采用扫描电子显微镜中的阴极发光显微术获得了YAG:Nd~(3+)激光晶体中不同缺陷所形成的显微发光图象。据此进一步分析了这些缺陷的形成机制及其对材料性能的影响。     

Luminescent and scintillation properties of YAG:Dy and YAG:Dy,Ce single crystalline films

The paper is devoted to investigation of the luminescent properties of Dy³⁺ and Dy³⁺-Ce³⁺ doped single crystalline films (SCF) grown by LPE method from PbO–B₂O₃ flux. We have found that the YAG:Dy and YAG:Dy,Ce SCFs possess bright cathodoluminescence in the visible range and good scintillation figure of merit. For this reason LPE grown YAG:Dy and YAG:Dy,Ce SCF are proposed for different applications, namely, as cathodoluminescence screens or screens for microimaging. The Dy³⁺ co-doping can be also proposed for improvement of the scintillation efficiency of the Ce³⁺ doped garnet compounds in the SCF form due to Dy³⁺→ Ce³⁺ energy transfer and removing the trap related centers in the above RT range.     

Stabilization of mixed valence by polaronic effects

Polaronic effects in mixed valence systems are studied in a simple model of localized d-electrons for arbitrary values of relevant parameters. Variational approach is used which permits one to interpolate between the limit of average static lattice distortion and that of different local distortions for different valence states of an ion. It is shown that the degree of local electron-lattice correlation and polaron narrowing of virtual f-level changes with a position of f-level. Polaronic effects make a valence transition more gradual and stabilize mixed valence phase. At the end some comments on a possibility of Valence Density Waves in mixed valence compounds are made and certain properties of CeAl₂ are tentatively ascribed to them.     

Investigation of the luminescence properties and thermal stability of dysprosium,terbium, and europium ions singly- and co-doped strontium yttrium borate phosphors

A series of trivalent rare-earth element ions (europium, terbium, dysprosium) singly- and co-doped strontium yttrium borate phosphors was synthesized via the sol–gel method. The phase formation, luminescence properties, decay times, and energy transfer behaviors from terbium ions to europium ions, the thermal stability, and the Commission Internationale de L’Eclairage coordinates were investigated. Under the excitation of ultraviolet light, the singly doped phosphors exhibited green emission of terbium ions, white emission of dysprosium ions, and red emission of europium ions, respectively. For the terbium and europium ions co-doped strontium yttrium borate samples, a white emission can be realized by blending the doping concentration of terbium and europium ions. The critical distance between terbium and europium ions has been calculated to be about 14.52?Å and the energy transfer from terbium to europium occurred through the dipole–quadrupole interaction. At 150°C, the emission intensity of terbium and europium in the 12?mol% terbium and 14?mol% europium co-doped strontium yttrium borate sample was maintained at about 74% and 87% of their corresponding initial values, respectively, and the dysprosium ions singly doped strontium yttrium borate sample showed about 70% of its initial emission intensity at room temperature. The above results suggested that europium, terbium, dysprosium ions singly- and co-doped strontium yttrium borate phosphors have potential applications as ultraviolet-convertible phosphors.