The nature of the C-defects in nickel and their rôle in the interpretation of radiation damage in metals

In previous Perturbed-Angular-Correlation (PAC) studies of the - emission of ¹¹¹In probe nuclei in cold-worked or particle-irradiated nickel, it has been found that thermal annealing in the temperature regime of recovery stage III leads to the formation of so-called C-defects (Cubic defects). This is indicated by the occurrence of a new frequency of about 80 Mrad/s, in addition to the frequency (200 Mrad/s) that is due to ¹¹¹In on substitutional sites. Obviously, the C-defects are complexes consisting of ¹¹¹In and the intrinsic point-defect species that migrates freely in recovery stage III. Therefore, they have played an important rôle in the long-standing controversy on whether the recovery-stage-III defects are vacancies (one-interstitial model) or self-interstitials (two-interstitial model). The present paper reports on a novel experimental effort to reveal the nature of the C-defects by combining PAC studies on nickel samples differently pretreated in a systematic way, investigations of the Extended X-ray Absorption Fine Structure (EXAFS) on In-doped nickel, and measurements of the decay rate of ¹¹¹In nuclei in the Electron-Capture-Induced Decay (ECID). On the basis of the results of these experiments it is concluded that the defects trapped by substitutional ¹¹¹In atoms (In_s) in recovery stage III are self-interstitials (I), as expected according to the two-interstitial model. Moreover, there is evidence that the C-defects are In interstitials on tetrahedral sites (In_i) that form exclusively in the vicinity of the specimen surface from In_s – I pairs via the reaction In_s+I In_i.     

Study of photophysical properties of capped CdS nanocrystals

Here, we have examined the role of capping agent on the optical properties of CdS nanoparticles by steady-state and time-resolved photoluminescence (PL) spectroscopy. The estimated particles sizes are 3.45, 2.5 and 2.39 nm for uncapped, capped with silica (SiO₂) and thiosalicylic acid (TSA), respectively. The absorption and emission spectra show a clear blue shift to shorter wavelengths in presence of TSA- and SiO₂-capped nanoparticles. It is found that the average decay time 〈τ〉 are 6.24, 4.54 and 2.84 ns for uncapped, capped with SiO₂ and TSA nanoparticles, respectively. Our analysis suggests that the hole or the electron is trapped on thiol molecule of TSA or hydroxyl group of SiO₂, then radiative recombination of the electron and hole is delayed, resulting in strong quenching of PL efficiency.     

Anwendung niederenergetischer Gammastrahler für radiographische Untersuchungen

An die zerstörungsfreie Materialprüfung mit Isotopen werden in unserem Lande erweiterte Forderungen gestellt, die sowohl die Prüfung von dünnwandigem Stahl als auch die Prüfung von Leichtmetallerzeugnissen beinhalten. Die Forderungen ergaben sich auf dem Gebiet, wo die Vorteile der γ-Defektoskopie im Vergleich mit der Röntgenprüfung in den Vordergrund treten. Die Strahlungsquellen Se-75 und Tm-170 schienen zu diesem Zweck die geeignetsten zu sein.     

Diffusion of nitrogen in vanadium and niobium

The diffusion of N in the group VB metals V and Nb has been studied in the previously uninvestigated temperature range 300–500 °C using ion-beam techniques. Diffusion couples were created by ion implantation. The time-dependent diffusion profiles were monitored by the use of the Nuclear Resonance Broadening (NRB) technique. New values for the solubility of N in Nb were obtained. The diffusion rates presented support recent observations of the diffusivity of interstitial impurities in body-centered cubic metals in which positive deviations from Arrhenius behaviour have been seen at high temperatures.     

Tm3+,Yb3+共掺钨酸钙多晶材料的上转换发光及荧光温度特性

采用高温固相法制备了Tm³⁺,Yb³共掺CaWO₄多晶材料. 980 nm二极管激光器激发下,在可见区获得了¹G₄→³H₆,¹G₄→³H₄,³H₂,³H₃→³H₆ 跃迁产生的上转换荧光. 讨论了Yb³⁺ 离子浓度的变化对Tm³⁺ 的上转换发光强度的影响,同时根据荧光强度比的方法研究了689 和705 nm 红色上转换荧光在313–773 K 范围内的温度特性. 结果表明：基于Tm³⁺,Yb³⁺ 共掺CaWO₄ 多晶材料的红色上转换荧光可以实现温度监测,其测温的最大灵敏度值为5.7×10^-4 K^-1,相应的测量温度为458 K. 关键词： 上转换发光 3+')" href="#">Tm³⁺ 钨酸钙 荧光温度传感     

Characterization of spectral hole depth in Tm^3＋ ：YAG within the cryogenic temperature range

In this paper, spectral hole depth dependence on temperature below 10 K in Tm^3＋ ：YAG crystal is investigated in detail. A novel model is proposed to analyze the temperature dependence on the spectral hole. By using the proposed model, we theoretically deduce the temperature dependence of spectral hole depth. The results are compared with experimental results and they are in good agreement. According to the theoretic results, the optimum temperature in experiment can be found.     

Multiferroic TbMnO3 nanoparticles

We report on the synthesis of TbMnO₃ nanoparticles by chemical co-precipitation route and their structural, chemical bonding, magnetic and dielectric properties. It is shown that the interesting multiferroic properties of this system as reflected by the concurrent occurrence of magnetic and dielectric transitions are retained in the nanoparticles (size∼40 nm). However, the nanoparticle constitution and properties are seen to depend significantly on the calcination temperature. While the nanoparticles obtained by calcination at 800 °C correspond very well with the reported properties of single phase TbMnO₃ (all the key magnetic and dielectric features near 7, 27 and 41 K, albeit with reduced dielectric constant) the nanoparticles obtained by calcination at 900 °C develop a Tb deficient skin which softens the transitions, reducing the dielectric constant further.     

Cr,Tm:YAG晶体中的能量转移

通过对Cr:YAG、Tm:YAG和Cr,Tm:YAG晶体吸收光谱和发射光谱的比较,研究了Cr,Tm:YAG晶体中的能量转移过程.指出Cr3+→Tm3+能量转移过程中,无辐射能量转移占绝对优势.     

Tm3+ ,Yb3+共掺微晶玻璃蓝色上转换荧光的温度特性

制备了Tm³⁺,Yb³⁺共掺氟氧化物微晶玻璃, 在980 nm二极管激光器泵浦下研究了其上转换发光。发现将前驱玻璃进行热处理后,源于Tm³⁺的¹G₄能级到基态³H₆跃迁所产生的蓝色上转换荧光在463 nm和476 nm出现明显劈裂。在此基础上分析了该劈裂蓝色上转换荧光在303~623 K范围内的温度特性。结果表明:Tm³⁺,Yb³⁺共掺氟氧化物微晶玻璃蓝色上转换荧光可应用于光学测温,其测温最大灵敏度为4.2×10^-4 K^-1,相应温度为352 K。     

α-TeO2∶Tm3+,Ho3+,Yb3+纳米材料的红绿蓝色上转换发光（英文）

利用简单的水热合成法成功制备出α-TeO2∶Ho3+,Yb3+、α-TeO2∶Tm3+,Yb3+和α-TeO2∶Tm3+,Ho3+,Yb3+纳米材料,用980 nm的近红外光作为激发光源测定了样品的室温上转换发射光谱。结果表明:样品α-TeO2∶Ho3+,Yb3+分别发射绿光(545 nm)和红光(651 nm),分别对应于Ho3+离子的5S2→5I8和5F5→5I8能级跃迁。随着Yb3+的摩尔分数从5%增加到15%,样品在545 nm处的绿光强度明显变大,发光颜色由黄光向绿光转变。样品α-TeO2∶Tm3+,Yb3+在476 nm处发射出蓝光,对应于Tm3+离子的1G4→3H6能级跃迁,两个弱红光峰(651,675 nm)分别对应于Tm3+离子的1G4→3F4和3F2→3H6能级跃迁。随着Yb3+离子浓度的提高,蓝光与红光的相对强度也在显著提高。基于可调控性蓝光、绿光和红光的产生,α-TeO2∶Tm3+,Ho3+,Yb3+纳米材料能产生不同颜色的光,包括白光。