An algorithm for unified analysis on the thermoluminescence glow curve

An algorithm was developed to integrally handle excitation by radiation, relaxation and luminescence by thermal or optical stimulation in thermoluminescence (TL) and optically stimulated luminescence (OSL) processes. This algorithm reflects the mutual interaction between traps through a conduction band. Electrons and holes are created by radiation in the beginning, and these electrons move to the trap through the conduction band. These holes move to the recombination center through a valence band. The ratio of the electrons allocated to each trap differs with the recombination probability and these values also relevant to the process of luminescence. Accordingly, the glow curve can be interpreted by taking the rate of electron–hole pairs created by ionizing radiation as a unique initial condition. This method differs from the conventional method of interpreting the measured glow curve with the initial electron concentration allocated to each trap at the end of irradiation. A program using the Visual Studio's C# subsystem was made to realize such a developed algorithm. To verify this algorithm it was applied to LiF:Mg,Cu,Si. The TL glow curve was deconvoluted with a model of five traps, one deep trap and one recombination center (RC).     

Thermoluminescence glow curve deconvolution of LiF:Mg,Cu,Si with more realistic kinetic models

Thermoluminescence (TL) glow curves of LiF:Mg,Cu,Si were deconvoluted with the introduction of enhanced physical model which envisages that both electrons and holes, produced by ionization radiation and trapped at the respective traps, can be thermally released into the conduction and the valence band, respectively and the holes may also radiatively recombine with electrons at the electron recombination centers. The model is more generalized than the ordinary trap interaction model which only permits the traffic of electrons through the conduction band. An effective numerical analysis method was developed to calculate the glow curve to be compatible with the measured curves. The validity of the numerical method was verified through artificially generated TL glow curves for a wide range of trap parameters. In order to identify TL kinetics of LiF:Mg,Cu,Si with higher accuracy, its glow curves were deconvoluted for two more generalized models, namely, the Schön–Klasens model and the Chen–Pagonis–Lawless model as well as the ordinary trap interactive model. The parameters in the more generalized multi-trap multi-recombination center (MTMR) model were found to be consistent with the quasi-static approximation(QSA) method.     

Method of Hoogenstraaten as a tool for obtaining the trap parameters of general-order thermoluminescence glow peaks

The Hoogenstraaten method is a technique that uses various heating rates for obtaining the activation energy E (eV) in the case of first-order thermoluminescence glow peaks. This method can also be used for obtaining E (eV) for all types of glow peaks regardless of their kinetics order (b). The present work shows that the intercept of the Hoogenstraaten relation, which is usually used for obtaining the frequency factor S (s ^?1) of the first-order glow peak, can be used as a very good approximation to obtain the pre-exponential factor S ^{′ ′} (s ^?1) in the case of general-order glow peaks, when one uses Hoogenstraaten’s method to obtain E (eV). In addition, the present work suggests a numerical method for obtaining the kinetics order of the general-order glow peak. The method depends on the activation energy E (eV) obtained by the Hoogenstraaten method and the above-mentioned approximation for obtaining the pre-exponential factor S ^{′ ′} (s ^?1). An independent evaluation of the suggested methods for obtaining the trap parameters, the activation energy E (eV), the pre-exponential factor S ^{′ ′} (s ^?1) and the kinetics order (b) is illustrated here by taking a numerically computed glow peak and applying a one-trap and one-recombination-center model.     

高压下KMgF_3晶体光学性质的第一性原理研究

本文采用第一性原理的方法,在100 GPa的压力范围内,计算了KMgF_3的理想晶体和含空位缺陷晶体的光学性质.吸收谱数据表明,在100 GPa范围内,压力因素不会导致KMgF_3晶体在可见光区有光吸收行为.钾、镁和氟空位缺陷的存在会使得KMgF_3晶体的吸收边红移(其中氟空位缺陷引起的红移最显著),但这些红移不会导致它在可见光区出现光吸收的现象.能量损失谱数据显示,压力因素不仅会使得KMgF_3晶体的能量损失谱有蓝移的行为,而且还会引起它的较强谱峰个数发生变化.在100 GPa处的缺陷晶体数据指明,氟空位缺陷会导致其能量损失谱的两个较强谱峰的峰值强度明显降低.分析表明,KMgF_3晶体有成为冲击窗口材料的可能,并且本文所获得的结果对未来的实验探究有参考作用.     

Applications of the three points analysis method for obtaining the trap parameters and the separation of thermoluminescence glow curve into its components

Here, we apply a recently developed technique to separate a composite thermoluminescence (TL) glow curve into its individual components and to evaluate the trap parameters of the individual TL glow peaks. These parameters include the order of kinetics b, the activation energy E (eV) and the frequency factor S (s^?1) or the pre-exponential factor S″ (s^?1). Recently, a general equation was developed to estimate the order of kinetics b. The characteristic point of this equation is that any set of three data points in a TL glow curve can yield b. Using this characteristic, an improved procedure was suggested to separate a composite glow curve, which includes several overlapping peaks, into its individual components and to obtain the trap parameters of the individual glow peaks. The method was applied here to analyze and determine the trap parameters of the TL glow curve of the promising TL dosimetric material, double potassium yttrium fluoride (K₂YF₅) doped with praseodymium ions (Pr³⁺), in response to γ-irradiation.     

银颗粒对Lu2O3:Eu薄膜光学性质影响

采用溶胶凝胶和提拉法制备了含有银颗粒的Lu2O3:Eu薄膜,利用X射线衍射,吸收光谱,光致发光光谱(PL)及荧光衰减光谱对其进行了表征,结果表明:所得材料在800℃下结晶完好,在发射光谱中观察到了银颗粒导致的Eu3 的发光增强效应,讨论了银颗粒对LU2O3:Eu薄膜发光性质的影响.     

YAlO3：（Nd^3＋,Lu^3＋）单晶的各向异性吸收光谱

在室温下测量了ＹＡｌＯ３：（Ｎｄ＾３＋，Ｌｕ＾３＋）单昌三个晶轴方向的吸收光谱。其吸收谱带强度明显呈各向异生。将Ｊｕｄｄ－Ｏｆｅｌｔ理论加以修正，并扩展应用于处理各晶轴方向的吸收光谱。     

Cathodoluminescence of Lu 2 O 3 :Tb

Spectroscopic properties of Lu 2 O 3 :Tb pellets sintered at 1000 v C or 1700 v C were investigated. The sintering temperature did not influence the optically excited emission and excitation spectra of the materials. However, the treatment temperature did influence the emission under cathode-rays stimulation. While the specimens sintered at 1000 v C showed only luminescent lines above 480 v nm resulting from a radiative relaxation of the 5 D 4 level, the samples heated at 1700 v C did show some luminescence in the blue region resulting from 5 D 3 M 7 F J emission. The blue emission could be recorded exclusively upon cathode-rays irradiation.     

The glow curve structure for the LiF:Mg,Cu,Na,Si TL detector with dopants concentrations and sintering temperatures

The glow curve structures for LiF:Mg,Cu,Na,Si TL detectors with various dopant concentrations and sintering temperatures were investigated for the improvement of the glow curve structure and sensitivity of the TL detector. The dopant concentrations were varied over the following ranges: Mg (0–0.25 mol%), Cu (0–0.07 mol%), Na and Si (0–1.5 mol%). With increasing Cu concentration, the intensity of the main peak was intensified and reached a maximum at a concentration of 0.05 mol%. The high-temperature peak was reduced. The dependency of the main peak intensity on the Mg concentration exhibits a sharp maximum at 0.2 mol%. The intensity of the high-temperature peak tends to rise slightly with increasing Mg concentration. It was found that the optimum concentrations of the dopants in the LiF:Mg,Cu,Na,Si TL material are Mg: 0.2 mol%, Cu: 0.05 mol%, Na and Si: 0.9 mol%. The dependency of the main peak intensity on sintering temperature exhibits a very sharp maximum at 830°C. The high-temperature peak was rapidly reduced after 825°C.     

Lu2O3：Tb纳米粉末的光致发光特性

用燃烧合成法制备了Lu₂O₃:Tb³⁺纳米粉末。产物为立方相结构,粒径在3~40nm之间可控。对不同颗粒度的样品的激发光谱、发射光谱和荧光衰减特性进行了研究。在紫外光激发下,样品显示出较强的发光(来自于Tb³⁺的⁵D_3,4→⁷F_J跃迁)。同时,样品的光致发光性质在很大程度上受到样品颗粒度的影响,对此现象给出了合理的解释。     

Further study on the influence of thermal treatments on the glow curve structure in LiF:Mg,Cu,P (GR-200A)

The influence of various annealing treatments with heating temperatures (T_A) from 240 to 700 °C, with re-annealing at 240 °C, and with a combined re-annealing procedure of 20 min at 270 °C followed by 10 min at 240 °C on LiF:Mg,Cu,P (GR-200A) was investigated. As the T_A increased, the intensity decreased rapidly to almost no signal at 340–380 °C then increased clearly and achieved a maximum at 540 °C. The position of the maximum intensity of the glow curve shifted basically in the direction of higher temperatures with an increase at T_A and achieved a maximum of 279 °C when annealed at 460 °C. The re-annealing influenced both the intensity and the glow curve structure at certain degree. The effect of re-annealing on the glow curve depended markedly on the T_A. With re-annealing at 240 °C, the intensity decreased as T_A increased up to 360 °C then increased and achieved a maximum at 540 °C. The intensity could be restored fully when annealed at above 500 °C, however, the glow curve couldn't be restored fully. With a combined annealing, the shape of glow curve of a sample annealed at above 540 °C or below 320 °C was similar to that of the standard glow curve of LiF:Mg,Cu,P and the intensity and glow curve could be restored completely when annealed in the range 620–660 °C. It seems that the main roles of the re-annealing at 240 °C are to restore partially the intensity of peak 4 and peak shape for LiF:Mg,Cu,P when annealed at above 260 °C, and restore fully the total TL intensity of LiF:Mg,Cu,P when annealed at above 500 °C and the main roles of the combined re-annealing are to reduce the intensity of peak 5 and the total TL intensity, increase the intensity of peak 4 and restore the glow curve shape.     

The effects of deep trap population on the thermoluminescence of Al2O3:C

The influence of deep traps on the 450 K thermoluminescence (TL) peak of Al₂O₃:C is studied. Depending upon the sample and on the degree of deep trap filling, features such as the TL width, area and height can vary considerably. These effects are interpreted to be due to: (a) sensitivity changes introduced by competition mechanisms involving deep electron and hole traps, and (b) the multiple component nature of the 450 K TL peak. The influence of the deep traps on the TL was studied using different excitation sources (beta irradiation or UV illumination), and step annealing procedures. Optical absorption measurements were used to monitor the concentration of F- and F⁺-centers. The data lead to the suggestion that the competing deep traps which become unstable at 800–875 K are hole traps, and that the competing deep traps which become unstable at 1100–1200 K are electron traps. Both the dose response of the TL signal and the TL sensitivity are shown to be influenced by sensitization and desensitization processes caused by the filling of deep electron and hole traps, respectively. Changes in the TL peak at low doses were also shown to be connected to the degree of filling of deep traps, emphasizing the influence of deep trap concentration and dose history of each sample in determining the TL properties of the material. Implications of these results for the optically stimulated luminescence properties are also discussed.     

Si,Lu掺杂Ca0.8Zn0.2TiO3:Pr3+荧光粉的光学性能改善

采用高温固相法合成Ca_0.8Zn_0.2TiO₃：0.2% Pr³⁺,Si⁴⁺和Ca_0.8Zn_0.2TiO₃：0.2% Pr³⁺,Si⁴⁺,Lu³⁺荧光粉。通过X射线衍射仪、电子顺磁共振光谱仪、显微拉曼光谱仪和荧光光谱仪等表征了该系列荧光粉的物相组成、微观结构和发光性质。结果表明,以β-Si₃N₄为硅源制备的荧光粉具有最佳的光学性能。加入ZnO后,荧光粉由CaTiO₃、Zn₂TiO₄和Ca₂Zn₄Ti₁₆O₃₈三相组成,其中CaTiO₃为主相。电子顺磁共振谱证实了Pr⁴⁺存在,Lu³⁺的添加使[Pr⁴⁺Ti³⁺O₃]⁺簇显著增加,电子顺磁共振谱和拉曼光谱均证实Si⁴⁺、Lu³⁺的掺杂使局部TiO₆簇对称性提高,有利于Pr³⁺发光中心的能量传递。在336 nm激发下,荧光粉展示了很强的位于612 nm的红光发射（归属于Pr³⁺的¹D₂→³H₄跃迁）及理想的红光色坐标（x=0.670,y=0.330）。Si⁴⁺和Lu³⁺的添加显著增强了370 nm激发下红光发射,Ca_0.8Zn_0.2TiO₃：0.2% Pr³⁺,3.2% Si⁴⁺荧光粉的余辉寿命最长。     

Nanodosimetric kinetic model incorporating localized and delocalized recombination: Application to the prediction of the electron dose response of the peak 5a/5 ratio in the glow curve of LiF:Mg,Ti (TLD-100)

A kinetic model combining both localized and delocalized recombination is described which is based on different filling rates as a function of irradiation electron energy of a spatially correlated trapping center/luminescent center (TC/LC) complex. Following irradiation and thermal de-trapping the locally trapped electron-hole configuration is assumed to give rise to peak 5a and the e-only configuration to peak 5 in the glow curve of LiF:Mg,Ti (TLD-100). The model is capable of simulating the linear/supralinear dose response of composite peak 5, the dependence of the supralinearity on photon energy and the ratio of the intensities of peak 5a to peak 5 as a function of dose. However, this is achieved only by invoking the presence of band-tail states which allow thermally induced hopping leading to semi-localized recombination in the recombination mechanism of the e-only configuration.     

Spectroscope studies of YAlO_3: (Lu~(3 )Nd~(3 ))

An increase of the Nd~(3 ) doping concentration and an enhancement of the laser induced fluorescence in the single crystal of YAlO_3: (Lu~(3 ), Nd~(3 )) have been observed and are attributed to the size compensation effect. The low temperature (4.2K) fluorescence spectra indicate that the structure of the sharp lines arising from the radiative transitions of Nd~(3 ) ions is not changed by the existence of Lu~(3 ) ions, but the emission lines are inhomogeneously more broadened. Besides, it has been observed that the fluorescence due to the radiative transition from the Stark's sublevel R_2 of the metastable level ~4F_(3/2) to the sublevels Y_1 of the manifold ~4I_(11/2) decreases with decreasing temperature and the fluorescence arising from the transitions R_1→Y_1 is relatively increased. The experimental fact is qualitatively interpreted.     

Preliminary TL Studies of K2GdF5:Dy3+ exposed to photon and neutron radiation fields

Results of the investigation concerning thermoluminescence (TL) responses to X, gamma and neutron radiation fields for crystals of complex fluoride K₂GdF₅ undoped and doped with varying concentrations of Dy³⁺ ions are presented. Crystals doped with 5.0 at% Dy³⁺ have shown the most efficient TL response, with a linear response to doses for all the radiation fields. In the X rays range, the maximum TL response has been found to be 15 times more than the response for gamma. The fast and thermal neutron TL outputs were evaluated for K₂Gd_0.95Y_0.05F₅ and the contribution of the gamma component in the TL curve was estimated.     

Study of TL properties of LaAlO3:Ce,Dy crystals for UV dosimetry

Thermoluminescence properties of lanthanum aluminum oxide (LaAlO₃) crystals doped with optically active rare earth ions have been investigated for ultraviolet dosimetry purposes. Single crystals co-doped with 5.0 at.% of Ce³⁺ and 1.0 at.% of Dy³⁺ ions have two thermoluminescent (TL) peaks at 151 °C and 213 °C which can be sensitized after 1 h of UV exposure. The material shows very high TL output and linear response for UV spectral irradiance ranging from 0.04 to 1.20 mJ cm⁻², that corresponds to 10 times the TL response of the Al₂O₃:C oxides. From 0.62 to 148.0 mJ cm⁻² the dependence is linear with the logarithm of the spectral irradiance. The investigation demonstrates that LaAlO₃:Ce,Dy crystals are very attractive to be investigated as UV dosimeters.     

Mg2+、Al3+离子增强SrTiO3:Pr3+荧光体发光性能的研究

采用溶胶凝胶法成功制备了SrTiO3:Pr3+、SrTiO3:Pr3+, Mg2+及SrTiO3:Pr3+,Al3+荧光粉.通过XRD、PL谱及第一性原理计算对样品的晶体结构、光谱特性及发光增强机制进行了研究.研究结果表明:共掺杂后,SrTiO3:Pr3+荧光粉为单一组成的SrTiO3立方相,主发射锋位于617 nm,对应于Pr3+离子的1D2→3H4跃迁发射.SrTiO3:Pr3+,Mg2+ 及SrTiO3:Pr3+, Al3+荧光粉的发光强度分别是SrTiO3:Pr3+荧光粉发光强度的7倍和2倍,但主要发光机制没有改变.Mulliken布局分析表明,Mg2+、Al3+离子的掺入使SrTiO3:Pr3+荧光粉中Ti-O及Pr-O键的化学键增强、键长变短,SrTiO3:Pr3+基质向Pr3+离子发光中心的能量传递效率提高,导致SrTiO3:Pr3+,Mg2+ 及SrTiO3:Pr3+,Al3+荧光粉的发光效率提高.     

类星体3C345的光变周期特性

收集了类星体3C345光学B波段100多年来较为完备的观测数据,获得了其长期光变曲线.利用小波分析的方法对其中B波段28年的数据进行了多时间尺度分析,并用小波变换系数图展示了3C345光学B波段的爆发过程.通过研究发现了其中存在有450天,780天,1830天和3540天的近似光变周期.利用小波逆变换可以反映其光变在不同时间尺度上的演变特征,进而预测类星体3C345未来可能的光学爆发时间为2010年左右. 关键词： 小波分析方法 光变曲线 多时间尺度 小波变换系数图     

Role of Ti in the luminescence process of Al2O3:Si,Ti

Al₂O₃:Si,Ti, prepared under oxidizing condition at high temperature, gives PL emission around 430 nm when excited with 240 nm. The Al₂O₃:C, TL/OSL phosphor, also shows emission around 430 nm, which corresponds to characteristic emission of F-center. Thus, to identify the exact nature of luminescent center in Al₂O₃:Si,Ti, fluorescence lifetime measurement studies were carried out along with the PL,TL and OSL studies. The PL and TL in Al₂O₃:Si,Ti show emission around 430 nm and the time-resolved fluorescence studies show lifetime of about 43 μs for the 430 nm emission, which is much smaller than the reported lifetime of ∼35 ms for the 430 nm emission (F-center emission) in Al₂O₃:C phosphor. Therefore, the emission observed in Al₂O₃:Si,Ti phosphor was assigned to Ti⁴⁺ charge transfer transition. Fluorescence studies of Al₂O₃:Si,Ti do not show any traces of F and F⁺ centers. Also, Ti⁴⁺ does not show any change in the charge state after gamma-irradiation. On the basis of the above studies, a mechanism for TSL/OSL process in Al₂O₃:Si,Ti is proposed.