Ageing and thermal recovery of paramagnetic centers induced by electron irradiation in yttria-stabilized zirconia

We have used electron spin resonance spectroscopy to study the defects induced in yttria-stabilized zirconia (YSZ) single crystals by 2.5-MeV electron irradiations. Two paramagnetic centers are produced: the first one with an axial d 111 symmetry is similar to the trigonal Zr 3+ electron center (T center) found after X-ray irradiation or thermo-chemical reduction, whereas the second one is a new oxygen hole center with an axial d 100 symmetry different from the orthorhombic O m center induced by X-ray irradiation. At a fluence around 10 18 e/cm 2 , both centers are bleached out near 600 v K, like the corresponding X-ray induced defects. At a fluence around 10 19 e/cm 2 , defects are much more stable, since complete thermal bleaching occurs near 1000 v K. Accordingly, ageing of as-irradiated samples shows that high-dose defects at more stable than the low-dose ones.     

Spectroscopy of F 3 + -color centers in lithium fluoride crystals (review)

Results of investigations of radiative F ₃ ⁺ -color centers in lithium fluoride obtained by the methods of one- and two-photon absorption, polarization spectroscopy, and luminescence in singlet, triplet and triplet-singlet channels are reported. The scheme of energy levels of the F ₃ ⁺ -center is revised. The probabilities of singlet-triplet conversion and the rates of depletion of the lower triplet state in the range of 80–350 K are presented. Recommendations are given on the technology of radiative LiF coloration that provide an increase in the F ₃ ⁺ -center concentration and a decrease in the concentration of some other centers that prevent lasing on the LiF:F ₃ ⁺ active medium from being obtained. The phototransformations of color centers in LiF are analyzed. The parameters of lasers with LiF:F ₃ ⁺ active media that provide generation of radiation tunable in the green region of the spectrum are considered. Based on spectroscopic data the maximum attainable time characteristics of such lasers are discussed. The prospects for further investigations of LiF:F ₃ ⁺ lasers are outlined in brief. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 5, pp. 745–760, September–October, 1998.     

Luminescence of F + and F centers in YAlO3

In YAlO₃ crystals grown in vacuum or reduced by annealing at low oxygen pressure, the luminescence of F centers in the band at 420 nm, with τ=30 ms at 9 K, excited in the bands at 212 and 242 nm, as well as the luminescence of F ⁺ centers in the band at 355 nm, with τ=2.7 ns, excited in the main band at 220 nm and weaker bands at 190 and 288 nm, was detected. On the basis of the results obtained and data in the literature, the behavior of the emission of F ⁺ and F centers in oxides of the Al₂O₃-Y₂O₃ system is analyzed on the example of the compounds α-Al₂O₃, YAlO₃, and Y₃Al₅O₁₂. The role of antisite defects in the stabilization of F-like luminescence and absorption centers in multisublattice oxides is discussed.     

Structural and luminescent properties of silicon nanoparticles incorporated into zirconia matrix

An impact of mechanical stresses on structural and photoluminescent properties of Si nanoparticles (NPs) incorporated into the zirconia thin films is reported. The stresses are found to be responsible for important structural modifications of the NPs. The zirconia matrix doped with the NPs exhibits bright red photoluminescence (PL) at room temperature due to efficient quantum confinement of the photogenerated carriers in the nanoscale Si particles. Spectral position of the PL picks depends on: mean dimension of the NPs, their concentration, stress induced deformation and order degree of the near-surface region. In general, zirconia matrix appears as a robust and reliable host media for Si NPs.     

Studies of the structure of Ce3+ centers in SrS phosphors

It is found that the shape of luminescence spectra of SrS−Ce phosphors is independent of both the species and concentration of a cofactor F, Cl, Br, or 1 introduced in the form of ammonium halide at least up to 6.5 at.%. The only exception is F, which, when added as a coactivator with a concentration of 2.4 at.% and above, gives rise to new longwave luminescence bands, part from the luminescence of the Ce³⁺ ion. Analysis has shown that this additional luminescence spectrum is similar to the Ce³⁺ spectrum but is shifted towards the longwave region by about 0.14 eV. The luminescence decay time constant (τ=57 nsec) is very close to Br, I, and small concentrations of F, a model is valid according to which the halogen that substitutes for sulfur and the Ce³⁺ that substitutes for Sr are the closest neighbors not to each other, but to a probable compensator of the charge of Sr vacancies. At high concentrations of fluorine some of the F ions are located at interstitial lattice sites in the immediate neighborhood of Ce³⁺, providing compensation for the charge of Ce³⁺ ions and having a marked effect on them. Tartu University, 18, Ulikooli St., Tartu EE2400, Estonian Republic. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 2, pp. 173–178, March–April, 1997.     

Luminescence and scintillation of Eu2+‐doped high silica glass

High silica glass doped with Eu²⁺ ions was prepared as a scintillating material by impregnation of Eu ions into a porous silica glass followed by reduction sintering in CO atmosphere. A dominant emission band of the Eu²⁺ 5d–4f transition peaking around 430 nm was observed in the luminescence spectrum with the excitation peak around 280 nm and no emission from Eu³⁺ was present. Photoluminescence decay kinetics was governed by decay times of a few microseconds. The Eu²⁺‐doped high silica glass exhibited comparable energy resolution and slightly higher photoelectron yield with respect to the Bi₄Ge₃O₁₂ crystal in the pulse height spectra for X‐ray photon energies within 22–60 keV. Furthermore, a factor of 1.2 higher radioluminescence intensity was observed as well. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

槲皮素-铝配合物合成过程中紫外-可见时间分辨吸收光谱

用氘灯光源室提供连续光,采用增强型光谱探测器ICCD拍摄光谱,利用DG535脉冲发生器对测量系统进行同步控制,实时测得了槲皮素与Al3 反应形成配合物过程中的紫外-可见时间分辨吸收光谱。光谱的曝光时间为1μs,每隔20ms拍摄1幅光谱,一次连续拍摄50幅。所拍光谱图清楚地显示出当反应进行到40ms时,槲皮素的两个特征峰254和374nm已消失,但在384nm处出现一过渡产物的吸收峰,而Al3 在300nm左右的特征吸收带仍存在;随着反应的进一步进行,过渡产物及Al3 在消失,槲皮素-铝配合物的特征峰267和436nm产生并逐渐增强;反应进行到980ms时,Al3 的特征吸收带完全消失,槲皮素-铝配合物的两特征吸收峰增至最强。整个反应过程在1s内已完成。文章结果提供了槲皮素具有清除Al3 的实验依据。     

二氧化锆纳米材料中Eu3+的发光特性

研究了掺1mol%Eu³⁺的二氧化锆纳米材料随退火温度变化的发光性质，得到退火温度为600和800℃的样品中Eu³⁺的⁵D₀→⁷F₂发射在604nm处，这种现象不多见. 几种经不同退火温度处理的纳米材料样品在紫外光的照射下，稀土离子Eu³⁺的⁵D₀→⁷F₂发射的发光逐 关键词： 二氧化锆 纳米材料 3+')" href="#">Eu³⁺ 发光     

Lifetime of F2 and F+3 centers in LiF crystals doped with magnesium

The influence of Mg impurity in an LiF crystal on the lifetime of the relaxed excited state of the F₂ and F⁺₃ centers is investigated for the first time by using the time-correlated photon counting technique at room temperature (RT). It is found that the radiative lifetime of the excited F₂ centers is almost independent of the Mg impurity concentration, while that of the excited F⁺₃ centers varies strongly with the corresponding impurity concentration.     

Nature of charge separation and recombination processes within an organic dyad having short spacer

With the help of electrochemical, steady state and time resolved fluorescence (fluorescence lifetimes by using time correlated single photon counting technique) and nanosecond laser flash photolysis methods, the nature of charge separation along with the energy wasting charge recombination processes within a short-chained organic dyad 1-(4-Bromo-phenyl)-3-(2-methoxy-naphthalen-1-yl)-propenone (MNBA) has been revealed. In MNBA, the donor 2-methoxynaphthalene (2MNT) is connected with the acceptor p-bromoacetophenone (PBA) by an unsaturated olefinic bond. Though in the ground state elongated type structure (E-form) is observable from NMR spectra but on photoexcitation, another conformers possibly of the nature of folded type isomeric species (termed as Z-isomer) were also apparent from time resolved fluorescence measurements. However, preponderance of elongated form in the excited singlet state has been established from this time resolved measurements. NMR study on photoirradiated sample and theoretical predictions from computations using CIS method with Lanl2DZ basis set also indicate in favor of the propositions made on the formations of the two possible conformers and the stability of elongated isomeric species in the electronic excited state from the experimental results. The energy wasting charge recombination rate, k_CR, determined from the transient absorption measurements by nanosecond laser flash photolysis (LFP) technique was found to be (k_CR, ∼1.9×10⁵ s⁻¹) significantly lower than the charge-separation rate, k_cs∼9.4×10⁷ s⁻¹, measured from the time resolved fluorescence. This observation demonstrates that MNBA may serve as an efficient candidate to construct artificial light energy conversion devices or components of molecular photovoltaic cells.     

Surfactant-assisted synthesis of defective zirconia mesophases and Pd/ZrO2: Crystalline structure and catalytic properties

Mesoporous zirconia nanophases with structural defects were synthesized by using a surfactant-templated method. Physicochemical properties and crystalline structures of the zirconia nanophases were studied by means of thermogravimetric analysis (TGA), N₂ physosorption isotherm and in situ Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques. The resultant materials show typical mesoporous features which vary with calcination temperature. The cationic surfactant in the network of the solids induces structural deformation and defect creation. The zirconia consists of monoclinic and tetragonal nanophases which contains many structural defects, and its crystalline structure shows microstrain. Both, concentration of lattice defects and degree of the crystal microstrain, decrease as the calcination temperature is increased. When CO is adsorbed on the surface of Pd/ZrO₂, linear bonds of CO–Pd⁰, CO–Pd^δ+ and CO–Zr⁴⁺ are formed, accompanying with CO₂ production. Catalytic evaluation shows that the Pd/ZrO₂ catalyst is very active for CO oxidation and NO reduction. In the case of oxygen absence from reaction mixture, high selectivity to N₂ is achieved without any NO₂ formation. In the oxygen rich condition, CO conversion is enhanced but less than 19% NO₂ is produced. N₂O is formed only in the reducing condition and its selectivity is sensitive to reaction temperature. The possible mechanisms of NO + CO and NO + CO + O₂ reactions over Pd/ZrO₂ catalyst related to reactant dissociation on the Pd metals and to defective structure of the nanozirconia support are discussed.     

Experimental and theoretical investigation of oxygen diffusion in stabilised zirconia

Oxygen diffusion in stabilised zirconias is investigated by the simultaneous application of computer modelling and experimental techniques to yttria-stabilised zirconia. Using the Mott-Littleton method, migration pathways for oxygen ions have been calculated in perfect cubic zirconia. The oxygen migration occurs through a straight pathway, but not starting from the ideal lattice positions. The calculated activation energy of migration is about 0.2 v eV. Oxygen transport is investigated experimentally in YSZ containing 8-24 v mol% Y 2 O 3 as a function of stabiliser content by combining the stable isotope ( 18 O 2 ) method with ionic conductivity measurements. It was found that for a given temperature, diffusion and conductivity are highest for YSZ containing 8-10 v mol% yttria, but with differing activation energies which can be compared to the calculated values.     

Structural,morphological and optoelectronic aspects of YAlO3:Dy3+ doped nanocrystalline materials for NUV energized WLEDs

Cost-effective urea assisted solution combustion (SC) synthetic method was employed to prepare a series of doped YAlO₃:xDy³⁺ (0.01–0.08 mol) phosphors. The resulting powdered samples were comprehensively examined through various structural as well as optical measurements. Rietveld refinement studies concluded that prepared nanomaterials structured into the orthorhombic system having Pbnm (62) space group. Energy dispersive spectral (EDS) analysis was executed to observe the relative proportions of constituent elements in all doped nanophosphors. Transmission electron microscopy (TEM) micrograph indicated the presence of agglomerated particles with the average size in the nano range. Photoluminescence excitation (PLE) spectra showed that the designated phosphors could be excited by near ultraviolet (NUV) energized lighting sources. The strongest emission centred at 576 nm, corresponding to electric dipole (⁴F_9/2 → ⁶H_13/2) transition of Dy(III) ion. Furthermore, characteristics photometric parameters viz. correlated color temperature (CCT), chromaticity coordinates (x and y), and color purity (%) were figure out with the aid of PL data, which strongly endorsed their usage in NUV energized WLEDs applications.     

Preparation and characterization of Tb and Tb(sal)3·nH2O doped PC:PMMA blend

Tb doped polycarbonate:poly(methyl methacrylate) (Tb-PC:PMMA) blend was prepared with varying proportions of PC and PMMA. Thermal and spectroscopic properties of the doped polymer have been investigated employing Fourier Transform Infrared (FTIR) absorption and differential scanning calorimetric (DSC) techniques. PC:PMMA blend (with 10 wt% PC and 90 wt% PMMA) shows better miscibility. Optical properties of the dopant Tb³⁺ ions have been investigated using UV-vis absorption and fluorescence excited by 355 nm radiation. It is seen that luminescence intensity of Tb³⁺ ion depends on PC:PMMA ratio and on Tb³⁺ ion concentration. Concentration quenching is seen for TbCl₃·6H₂O concentration larger than 4 wt%. Addition of salicylic acid to the polymer blend increases the luminescence from Tb³⁺ ions. Luminescence decay curve analysis affirms the non-radiative energy transfer from salicylic acid to Tb³⁺ ions, which is identified as the reason behind this enhancement.     

Tuneable laser operation of F+2 and (F+2)A centers in OH- and SH- doped alkali halides

Stabilization and tuneable laser operation of F⁺₂ and (F⁺₂)_A centers using OH^- and SH^- doped alkali halide crystals are reported. The new stabilization technique improves previously described laser systems and produced a new F⁺₂(KBr) laser (1.72–2 μm), covering an important gap around 2 μm. All crystals can easily be reactivated for laser operation after extended periods of storage at room temperature.     

掺杂Eu3+离子LaPO4的合成及其发光特性研究

采用固相反应法合成了掺杂Eu3+离子的LaPO4,并用X射线粉末衍射对其结构进行了表征.XRD数据经计算机处理表明:LaPO4属单斜晶系,晶胞参数a=6.84A,b=7.08A,c=6.46A,β=103.85°,属P21/n(No.14)空间群.测定了其激发光谱和发射光谱,光谱数据表明:在掺杂Eu3+离子的LaPO4荧光体中,基质LaPO4的电荷迁移激发态的能量能有效地传递到Eu3+离子,说明基质LaPO4本身对发光有贡献.位于592,612 nm附近的2个发射峰均出现劈裂现象,即有2个5D0→7F1(590,594nm)、2个5D0→7F2(610,614nm)发射峰,说明掺杂的Eu3+离子在LaPO4晶体中有着不相同的配位环境,推测Eu3+离子处于D2d或D3对称格位.     

Y3+和Gd3+对LaBO3:Eu3+发光粉结构和发光性能的影响

采用溶胶凝胶-燃烧法合成了系列不同掺杂浓度Y³⁺和Gd³⁺的LaBO₃∶Eu³⁺发光粉,对其结构、形貌和发光性能进行了表征。XRD研究结果表明：发光粉的结构与基质掺杂离子的种类和掺杂浓度有关系。荧光光谱结果表明：适量比例Y³⁺和Gd³⁺离子掺杂将提高LaBO₃∶Eu³⁺发光粉的发光强度。Y³⁺和Gd³⁺离子最佳掺杂摩尔分数分别为1.5%和12.5%。⁵D₀→⁷F₂与⁵D₀→⁷F₁跃迁发射的相对强度比值说明：掺杂改变LaBO₃∶Eu³⁺中Eu³⁺局域环境的对称性。发光性能改变主要受晶体结构、掺杂离子电负性影响。Gd³⁺离子掺杂更有利于发光粉结构稳定性和发光性能的改善。     

Luminescence of aggregate centers in CsBr:Eu2+ single crystals

We have used the Bridgman method to grow CsBr:Eu²⁺ single crystals, adding an activator to the mix in the form of Eu₂O₃ in amounts of 0.0125, 0.0250, and 0.0500 mole %. At T = 300 K, we studied the absorption spectra, the photoluminescence (PL) spectra, and the photostimulated luminescence (PSL) spectra of the grown crystals. We have established that the structure of the photoluminescence and photostimulated luminescence centers in crystals grown from the CsBr:Eu₂O₃ mix includes isolated dipole centers Eu²⁺-V_Cs, emitting in bands with maxima at 432 nm and 455 nm respectively, and in crystals grown at activator concentrations of 0.025 and 0.050 mole % they also include aggregate centers (AC) based on CsEuBr₃ nanocrystals with emission bands at 515 m and 523 nm. We have shown that the maximum concentration of aggregate centers of the CsEuBr₃ nanocrystal type in CsBr:Eu²⁺ crystals is achieved for an activator content in the mix within the range 0.01–0.05 mole %. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 359–362, May–June, 2006.     

Al3+掺杂BaFBr:Eu2+中F(Br-)心的性质

作为光激励发光的首选材料BaFBr:Eu^2 ，在其中掺杂一定量的Al^3 后，其光激励发光谱向长波方向发生了较大的红移现象，红移的机理是掺杂的Al^3 离子取代了BaFBr:Eu^2）晶格中的Ba^2 离子，且处于F（Br^-）心的次近邻位所致。本文利用喇曼光谱和电子顺磁共振谱对受掺杂Al^3 微扰的F（Br^-)心的结构进行了研究，首次在喇曼光谱的高频移区观测到了由于掺参Al^3 所引起的新结构的产生，通过电子顺磁共振谱表征了在BaFBr:Eu^2＋中Al^3 与F（Br^-）心的相对位置，并且得出F（Br^-)心与OF^-心存在着空间相关性。