Photo-stimulated emission of X-irradiated BaFBr:Eu

Abstract

The photo-stimulated luminescence (PSL) of Eu²⁺-doped BaFBr is excited in the two F centre absorption bands produced by X-irradiation at room temperature. The PSL intensity decreases with decreasing temperature by about a factor of 10. After bleaching at low temperatures the PSL is nearly zero, it can be regenerated by warming the crystal to room temperature. The results are discussed with a new model of the PSL process.     

Photostimulated luminescence properties of BaFBr:Eu under ion irradiation

The photostimulated luminescence (PSL) properties of the phosphor BaFBr:Eu after ion beam irradiation was analyzed; in particular, the PSL intensity dependent on ion fluence. The PSL intensity increased linearly with the ion fluence up to 10¹² ions/cm², and subsequently decreased gradually. The ion fluence dependence was observed to be similar among samples containing different F centers or different Eu concentrations. The fluence dependence was quantitatively analyzed based on a trapping model, in which competition between the trapping processes to storage centers and radiation defects is assumed; the model explained the experimental data quantitatively. The results indicate that radiation defects influence the PSL properties via the trapping of photostimulated electrons.     

New synthesis of high-quality storage phosphors

We present a single step synthesis method for the photostimulable X-ray storage phosphor BaFBr:Eu²⁺ which results in a highly sensitive powder with a relatively small average grain size of 5.4 μm. The starting chemical reagents are BaCO₃, NH₄F, NH₄Br and EuF₃. The reaction initiated by the decomposition of the ammonium materials leads to highly volatile hydrogen halide gases which react with the BaCO₃ to form BaFBr at temperatures up to 300 °C. Further heating results in the incorporation of Eu²⁺ and the formation of halide vacancies at temperatures in between 390 and 580 °C. The resulting photostimulated luminescence (PSL) efficiency is optimized after sintering at 800 °C. The reaction process is monitored by differential thermal analysis (DTA) and the reaction products are detected by mass-spectroscopy which confirms the proposed chemical reactions. Intermediate and final products are identified using X-ray diffraction. Photoluminescence (PL) and PSL spectra show the incorporation of Eu²⁺ into the lattice, as well as a PL peak at 470 nm which is not present in the PSL spectrum. This peak is shown to originate from O^2? in the lattice and directly affects the PSL sensitivity.     

The role of hydrogen- and hydroxyl-doping in CsBr:Eu

Hydrogen- and hydroxyl-doped CsBr:Eu²⁺ storage phosphors were investigated by photostimulated luminescence (PSL) spectra, absorption spectra and PSL lifetime spectra. Hydrogen- and hydroxyl-doping plays an active role related to the trap centers in CsBr:Eu²⁺ storage phosphors. A sharp increase in the PSL yield was observed for non-hydroxyl-doped CsBr:Eu²⁺ annealed in 5%H₂+95%Ar atmosphere. For hydroxyl-doped CsBr:Eu²⁺, the PSL lifetime (361 ns) is obviously shorter than that of typical CsBr:Eu²⁺ storage phosphors.     

BaFCl:Eu2+光激励读出过程中两种F色心的差异

研究了紫外线辐照下BaFCl:Eu²⁺的光激励发光性质.测定了在不同温度下经紫外线辐照后的光激励谱,变化范围为10—300K同时研究了两种F色心的光激励发光强度在激励读出过程中随温度的变化关系.分析了光激励谱产生差异的原因. 关键词：     

Crystal-Size Dependence of Replenishment Effect in BaFBr:Eu

Excitation spectra of photo-stimulated luminescence (PSL) in BaFBr:Eu and BaFBr:Eu ? Na crystals were studied. Replenishment of PSL at liquid helium temperature was investigated in crystals of various sizes including a commercially available X-ray storage phosphor plate (Image Plate). Although a weak replenishment effect was observed in the fine powder crystals, no replenishment effects were observed in Image Plate, while it showed strong PSL at liquid helium temperature. Results indicate that there are two types of PSL centers, one consists of spatially correlated electrons and holes and the other consists of electrons and holes trapped at isolated centers. Lack of the replenishment effect in Image Plate indicates that trapped electrons are stabilized by the surface and need thermal activation to recombine with holes which are possibly trapped at doped Eu^2?.     

Luminescence studies of thallium co-doped KBr:Eu2+ powder phosphors

In this study, photoluminescence (PL) and photostimulated luminescence (PSL) properties in KBr:Eu²⁺, Tl⁺ powder phosphors are reported. PL emission spectra of these Tl⁺ co-doped KBr:Eu²⁺ phosphors show four overlapping bands around 310, 325, 360 and 375 nm in addition to the characteristic of Eu²⁺ ions at 420 nm. These additional short wavelength bands were attributed to centres involving Tl⁺ ions. The decrease in PSL intensity of γ-irradiated KBr:Eu²⁺, Tl⁺ powder phosphors with Tl⁺ concentration and the absence of thallium emission bands in PSL were attributed to the efficient electron trapping by Tl⁺ ions during irradiation.     

Effects of excitation and bleaching of ultraviolet during photostimulated luminescence of BaFCl:Eu2+ phosphors

The photostimuated luminescence (PSL) of BaFCl:Eu²⁺ phosphors is studied through changing the energy of ultraviolet(UV)-irradiation. The PSL shows obviously difference while the irradiation energy is larger or smaller than that of the Eu²⁺ minimum excited state. The reasons for this difference are discussed and the location of the transform energy level of UV-irradiation from excitation to bleaching is given. Supported by National Natural Science Foundation of China.     

新型电子俘获型材料β-Sr2SiO4:Eu2+, La3+长余辉和光激励发光性能的研究

通过高温固相法在还原气体保护下制备出β-Sr₂SiO₄: Eu²⁺, La³⁺系列样品. 通过样品光谱显示, 光致发光、余辉及光激励发光中心均来自于Eu²⁺离子; 并且La³⁺ 的掺入有效增强光致发光、余辉及光激励发光强度. 热释光与余辉衰减测试证明, 与单掺Eu²⁺样品所具备的缺陷数量相比, 共掺La³⁺样品在浅陷阱区(T1区)较多的俘获中心数量是导致其余辉性能优化的主要因素; 其光激励发光强度的增强则归因于在深陷阱(T3区)的俘获中心数量增加. 共掺样品放置15h并在980nm红外激光激励后, 表现出光激励长余辉发光现象. 此现象的出现, 为电子俘获型材料的浅陷阱对深陷阱中的载流子再俘获过程的存在提供了直接证据. 因此, β-Sr₂ SiO₄: Eu²⁺, La³⁺ 材料可视为一种潜在的长余辉和光激励发光材料.     

Photostimulated luminescence of corrugated fiberboard as an additional screening method for detecting radiated foods

In this study, PSL of non-irradiated and irradiated corrugated fiberboards (CFs) was investigated to evaluate the possibility that CFs can be used as alternative specimens for the screening detection method of food irradiation. The irradiation at a dose of only 0.15 kGy increased PSL signals of the CF over 1 order of magnitude. The PSL signals increased with increasing in gamma irradiation dose and became almost saturated at a dose of 5 kGy. The core of CFs showed PSL signals sufficient for distinguishing irradiated from non-irradiated at least 6 months after irradiation even though the CF was exposed to light and the environmental temperature increased to 50 °C. These results suggest that the PSL property of the core of CFs is useful for detecting irradiation. However, the large variation of PSL signals among CFs made it difficult to set a well-defined “positive” threshold limit to distinguish irradiated from non-irradiated completely. All of the non-irradiated CFs showed PSL signals above 10³ counts, which is much higher than that detected for foods. It is apparent that the threshold limit of EN 13751 is not applicable to detecting irradiated CFs. More detailed collaborative research with large number of samples is needed to establish new threshold limits involving “intermediate” classification.     

光激励发光的并行模型

分析了目前存在的两种光激励发光理论模型，并基于对光激励发光中电子转移过程的分析，提出了光激励发光的并行模型.通过求解，得出了描述光激励发光过程的一般公式.制备了光激励发光材料BaFCl:Eu²⁺，对其进行了系统的光谱测试.利用实验结果，从衰减规律、两种色心的差异以及X射线辐照剂量与光激励发光强度间的关系等方面对这一模型进行了验证. 关键词：     

Eu^2＋：BaFCl光激励发光衰减的研究

制备了系列材料Ｅｕ＾２＋：ＢａＦＣｌ，测量了其光激励发光的衰减曲线，基于隧穿模型，建立了描述隧穿过程的数学模型，得出了光激励发光衰减规律，并将结果与实验进行了比较。     

Critical distance for secondary ion formation: Experimental SIMS measurements

We have performed direct experimental measurements of the critical distance for the secondary ion formation process. To this end, we compared the experimentally measured energy distribution of secondary Si⁻ ions with the theoretical energy distribution (Sigmund-Thompson relation) of secondary Si atoms. Our model states that the maxima positions of these two energy distributions differ by the Coulomb interaction potential between the outgoing ion (Si⁻ in our case) and a charge with the opposite polarity formed at the surface after electron transition between the outgoing Si atom and the surface. Quite a reasonable value was obtained for the critical distance, but with a large scatter in experimental data. The conclusion has been made that the experimental technique should be improved to get more precise values of the critical distance, which is of high importance for practical purposes.     

电子俘获光存储材料BaLiF3:Eu2+的光激励发光及光存储性质研究

利用高温固相反应法制备了混晶状的BaLiF3:Eu2 样品.其紫外光激发的发射峰与光激励发光峰均在410 nm处,属于Eu2 的5d-4f跃迁发光.光激励峰位于660 nm,因而可以配用简单廉价的氦氖激光器.根据光谱特征给出了光激励发光的简单机理.测量了该材料光激励发光衰减性能,结果表明BaLiF3:Eu2 存储的信息可以方便地擦除掉.该材料具有优良的光激励发光特性,是一类很有发展前途的电子俘获光存储材料.     

Red-shift in the photostimulation of the X-ray storage phosphor RbBr:Ga+

Abstract

By means of magnetic circular dichroism of the optical absorption and photostimulated luminescence (PSL) the X-ray induced formation of F_A and F centres in RbBr:(Ga⁺, Li⁺) was investigated. It turnes out that RbBr:Ga⁺ co-doped with 1% Li⁺ in the melt reveals the largest red-shift of the PSL excitation bands to 790 nm, whereby the F_A to F ratio increases up to about 10% with decreasing X-ray dose. This is more than statistically expected (6%). High X-ray doses destroy F_A centres. However, up to 15% of the simultaneously generated F centres could be converted into the F_A species by appropriate bleaching with 633 nm light into the F centre absorption band.     

Effect of isoelectronic impurities K<Superscript>+</Superscript> and I<Superscript>−</Superscript> on luminescence of CsBr:Eu<Superscript>2+</Superscript> crystals

We have investigated the photoluminescence (PL) and photostimulated luminescence (PSL) spectra at 300 K to study the effect of isoelectronic impurities K⁺ and I⁻ on the formation and energy structure of Eu²⁺-V_Cs isolated dipole centers and aggregate centers in the form of single crystals of CsEuBr₃ in CsBr:Eu²⁺ single crystals. We have shown that K⁺ and I⁻ impurities in a concentration of 5 mol% do not have a substantial effect on the energy spectrum of isolated dipole centers in CsBr:Eu²⁺ single crystals and the processes for the formation of such centers during growth of CsBr:Eu single crystals from the melt by the Bridgman method. We have established that in Cs_0.95K^0.05Br:Eu²⁺, more favorable conditions are realized for the formation of aggregate centers than in CsBr:Eu²⁺ and CsBr^0.95K^0.05Br:Eu²⁺ single crystals. So in order to improve the storage properties of phosphors based on CsBr:Eu²⁺, in particular for increasing the efficiency of PSL excitation, it is expedient to dope them with K⁺ impurity in a concentration up to 5 mol%. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 627–630, September–October, 2007.     

Comparison of the cytotoxic effect of polystyrene latex nanoparticles on planktonic cells and bacterial biofilms

The cytotoxic effect of positively charged polystyrene latex nanoparticles (PSL NPs) was compared between planktonic bacterial cells and bacterial biofilms using confocal laser scanning microscopy, atomic force microscopy, and a colony counting method. Pseudomonas fluorescens, which is commonly used in biofilm studies, was employed as the model bacteria. We found that the negatively charged bacterial surface of the planktonic cells was almost completely covered with positively charged PSL NPs, leading to cell death, as indicated by the NP concentration being greater than that required to achieve single layer coverage. In addition, the relationship between surface coverage and cell viability of P. fluorescens cells correlated well with the findings in other bacterial cells (Escherichia coli and Lactococcus lactis). However, most of the bacterial cells that formed the biofilm were viable despite the positively charged PSL NPs being highly toxic to planktonic bacterial cells. This indicated that bacterial cells embedded in the biofilm were protected by self-produced extracellular polymeric substances (EPS) that provide resistance to antibacterial agents. In conclusion, mature biofilms covered with EPS exhibit resistance to NP toxicity as well as antibacterial agents.     

Effect of halide ion concentration and irradiation dose dependent photostimulated luminescence investigation in the image screen phosphor CsBr1-xClx:Euy 2+

Photoluminescence(PL) characterization is carried out on CsBr_1-xCl_x:Eu_y²⁺ (x = 0.05, 0.1, 0.2, 0.3 y = 100 ppm, 200 ppm) crystals grown in vacuum with the Bridgman technique. PL studies show an increase in luminescence intensity with a decrease in bromide ion content. F(Br^–) and F(Cl^–) centers are formed due to -ray irradiation at room temperature. Photostimulated luminescence (PSL) emission is found to increase with an increase in irradiation dose from 7.5 Gy to 30 Gy at room temperature. From the results it is demonstrated that out of the different compositions studied, CsBr_0.9Cl_0.1:Eu²⁺ (200 ppm) phosphor has a linear PSL response with respect to irradiation dose.     

Objective Stenosis Quantification From Post-Stenotic Signal Loss in Phase-Contrast Magnetic Resonance Angiographic Datasets of Flow Phantoms and Renal Arteries

In this study a semi-automated and observer-independent algorithm for quantifying post-stenotic signal loss (PSL) in three-dimensional phase-contrast (PC) magnetic resonance angiography (MRA) of patients with renal artery stenosis is presented. This algorithm was developed on MRA datasets of stenotic phantoms, included in a flow circuit with stationary flows. The length and the severity of the PSL (incorporating both the length and the degree of PSL) in the MRA datasets were proposed for quantifying the stenoses. The algorithm was tested in renal arteries; ten patients with renal artery stenosis and seven healthy volunteers were investigated. Digital subtraction angiography was performed in the patients and served as the gold standard. Stenosis severity showed better correlation with the severity of the PSL than with the length, both for in vitro and in vivo measurements. Spearman correlation coefficients (r_s) showed statistically significant correlations between the severity of the PSL and parameters determined by digital subtraction angiography, i.e., percent diameter stenosis (r_s = 0.90). The length of the PSL showed no correlation with the diameter stenosis (r_s = 0.37). In conclusion, this study presents a semi-automated and observer-independent way of quantifying signal loss, and the severity of the PSL is proposed for quantifying stenoses, rather than the length of PSL.     

多孔硅结构与发光机理的非线性光学研究

最近的研究中,采用1.06μm超短脉冲光激发,在多孔硅表面观察到了有效的红外多光子激发的荧光发射.研究表明,这是一个增强的三阶非线性光学过程.本文利用其三阶非线性特性对具有强可见光发射的多孔硅结构进行了研究,结果显示晶体硅的各向异性特征在多孔硅中几乎被保留;此外,较强的激光激发导致的红外上转换荧光信号衰减过程被归结为与多孔硅表面氢的脱附有关.