Gd3(Al,Ga)5O12:Ce闪烁晶体缺陷对其发光性能的影响

新型闪烁晶体Gd₃(Al,Ga)₅O₁₂:Ce(GAGG:Ce)在制备过程中易出现包裹体及反格位缺陷等问题,严重影响晶体的性能.为了抑制这些缺陷以得到大尺寸高质量的GAGG:Ce晶体,本文以Gd₃(Al,Ga)₅O₁₂为基质、Ce3+为掺杂离子,采用提拉法生长得到了GAGG:Ce晶体,并对不同晶体部位的物相结构、微区成分、透光性质、发光及时间性能进行了测试和对比分析.结果表明,GAGG:Ce晶体的透过谱中存在340和440 nm两处Ce³⁺特征吸收带,且位于550 nm处的直线透过率为82%.晶体尾部因杂相包裹体等宏观缺陷的影响,导致其透过率下降至70%左右.微区成分分析进一步表明GAGG:Ce晶体中存在三种类型的包裹体,分别为富Gd相、富Ce相及(Al,Ga)₂O₃相.GAGG:Ce晶体的X射线激发发射谱中在550 nm附近存在Ce³⁺宽发射带,且380 nm处还存在GdAl/Ga反格位缺陷引起的发射.晶体中存在的杂相包裹体及GdAl/Ga反格位缺陷等因素导致Ce³⁺在GAGG基质的发光强度下降12.5%;GdAl/Ga反格位离子与近邻Ce的隧穿效应使得GAGG:Ce晶体的衰减时间由117.7 ns延长至121.9 ns,且慢分量比例由16%增加至17.2%.     

Luminescence and scintillation properties of YAG:Ce single crystal and optical ceramics

We use various techniques to study optical and scintillation properties of Ce-doped yttrium aluminum garnet, Y₃Al₅O₁₂ (YAG:Ce), in the form of a high-quality industrial single crystal. This was compared to optical ceramics prepared from YAG:Ce nanopowders. We present experimental data in the areas of optical absorption, radioluminescence, scintillation decay, photoelectron yield, thermally stimulated luminescence and radiation-induced absorption. The results point to an interesting feature—the absence of antisite (Y_Al, i.e. Y at the Al site) defects in optical ceramics. The scintillation decay of the ceramics is faster than that of the single crystal, but its photoelectron yield (measured with 1 μs integration time) is about 30-40% lower. Apart from the photoelectron yield value the YAG:Ce optical ceramic is fully comparable to a high quality industrial YAG:Ce single crystal and can become a competitive scintillator material.     

Imaging performance and light emission efficiency of Lu<Subscript>2</Subscript> SiO<Subscript>5</Subscript>:Ce (LSO:Ce) powder scintillator under X-ray mammographic conditions

The aim of the present study was to measure the imaging transfer characteristics and the luminescence efficiency (XLE) of a Lu₂SiO₅:Ce (LSO:Ce) powder scintillator for use in X-ray mammography detectors. An LSO:Ce powder scintillating screen, with a coating thickness of 25 mg/cm², was prepared in our laboratory. The imaging performance of the screen was assessed by experimental determination of the modulation transfer function (MTF) and the detective quantum efficiency (DQE) as well as single index image quality parameters such as noise equivalent pass band (Ne) and informational efficiency (n _I). A theoretical model, describing radiation and light transfer, was fitted to experimental MTF values in order to estimate optical properties of the scintillator. Screen irradiation was performed under exposure conditions employed in mammographic applications (27 kVp, 63 mAs). MTF was determined by the square wave response function (SWRF) method. Results showed that LSO:Ce exhibits high MTF and DQE values, which are comparable to those of the commercially used Gd₂O₂S:Tb. Considering our image quality parameters and luminescence efficiency results as well as the fast response of the LSO:Ce scintillator screen (40 ns), this material can be considered for use in X-ray mammographic detectors.     

Luminescence properties of the Mg co–doped Ce:SrHfO3 ceramics prepared by the Spark Plasma Sintering Method

1300 or 1400 °C pre–sintered Al/Ce/Mg:SrHfO₃ and Al/Ce:SrHfO₃ ceramics were prepared by the Spark Plasma Sintering (SPS) in order to search for a new scintillation material with a high–effective atomic number(Z_eff) and good light output. The SrHfO₃ has a high Z_eff of 60, and high gamma–ray detection efficiency is expected. Meanwhile it has a high melting point of over 2500 °C, and single crystal is hard to be grown. On the other hand, high melting materials can be prepared as ceramics, and the SPS method is a simple process to fabricate the ceramics within a few hours. Thus, we prepared the samples using the SPS method, and their optical and scintillation properties were investigated. We found that Al/Ce/Mg:SrHfO₃ and Al/Ce:SrHfO₃ ceramics had an emission wavelength at around 400 nm originating from 5d–4f transition of Ce³⁺. Moreover, Al/Ce/Mg:SrHfO₃ pre-sintered at a temperature of 1400 °C had a light output of approximately 5,000 ph/MeV. In this paper, the light output of Mg-co-doped samples was improved compared with the Mg-free ones. The light output also depends on the pre-sintering temperature.     

Optimization of neon soft X-rays emission from 200 J fast miniature dense plasma focus device: A potential source for soft X-ray lithography

The neon soft X-ray (SXR) emission characteristics of a Fast Miniature Plasma Focus (FMPF-3) device have been investigated. The FMPF-3 device used for our experiment is of sub-kilojoule energy capacity, which is an order of magnitude lesser than the other well established plasma focus devices. The influence of different geometrical parameters of the anode and the pressure of the filling gas on the SXR emission was investigated to optimize the neon SXR yield and thereby make it a potential source for X-ray lithography. The SXR signal, solely from the desired, characteristic spectral range (900–1600) eV was selectively extracted and acquired using appropriate X-ray absorption filters on diode X-ray spectrometer. It was found that the neon SXR emission from 17 mm long cylindrical anode, which produced best neutron yields, was rather poor, in a very narrow pressure range and that too at low operating pressure. With decrease in the length of cylindrical anode, the optimum operating pressure shifts to higher pressure side, the working pressure range widens and the SXR yield also increases until the anode length is reduced to 12 mm, after which, the SXR yield and working pressure range start to degrade. The highest neon SXR yield of 1.1 J/shot, corresponding to a wall plug efficiency of 0.57%, was obtained for 12 mm long cylindrical anode. The tapered anodes with different length were also designed and tested, but they did not show any significant improvement in neon SXR yield.     

5d→4f transition in halosulphate phosphors

The synthesis, X-ray diffraction and photoluminescence characteristics in alkaline halosulphate phosphors, such as KZnSO₄Cl:Ce; KMgSO₄Cl:Ce; NaMgSO₄F:Ce and Na₃SO₄F:Ce is reported in this paper. The Ce³⁺ emission in KMgSO₄Cl:Ce phosphor is maximum and it may be useful for scintillation applications.     

Scintillation timing characteristics of (La,Gd)2Si2O7:Ce and Gd2SiO5:Ce single crystal scintillators: A comparative study

The scintillation timing characteristics of (La,Gd)₂Si₂O₇:Ce (GPSLa23.5%:Ce) single crystal were studied and compared with Gd₂SiO₅:Ce (GSO:Ce) single crystal. The photoelectron yield, scintillation decay times and coincidence time resolution were measured. At 511 keV γ-rays, the photoelectron yield of 10,770 ± 500 phe MeV⁻¹ and energy resolution of 5.4 ± 0.2% obtained for GPSLa23.5%:Ce are much better than those of 3350 ± 160 phe MeV⁻¹ and 7.8 ± 0.3% obtained for GSO:Ce. The scintillation decay time profile was measured by the time-correlated single photon counting technique using a fast-slow coincidence setup. In both materials the comparable rise times of several nanoseconds are present. The fast component decay time of 56 ns with relative intensity of 49% obtained for GPSLa23.5%:Ce is inferior to that of 32 ns(88%) obtained for GSO:Ce. Consequently, the coincidence time resolution of GPSLa23.5%:Ce is slightly worse than that of GSO:Ce. The normalized time resolution was also discussed in terms of a number of photoelectrons and decay time of the scintillation pulse.     

Scintillation and optical stimulated luminescence of Ce-doped CaF2

Scintillation and optical stimulated luminescence of Ce 0.1–20% doped CaF₂ crystals prepared by Tokuyama Corp. were investigated. In X-ray induced scintillation spectra, luminescence due to Ce³⁺ 5d–4f transition appeared around 320 nm with typically 40 ns decay time. By ²⁴¹Am 5.5 MeV α-ray irradiation, 0.1% doped one showed the highest scintillation light yield and the light yield monotonically decreased with Ce concentrations. Optically stimulated luminescence after X-ray irradiation was observed around 320 nm under 550 or 830 nm stimulation in all samples. As a result, intensities of optically stimulated luminescence were proportional to Ce concentrations. Consequently, scintillation and optically stimulated luminescence resulted to have a complementary relation in Ce-doped CaF₂ system.     

Highly Efficient and Flexible Scintillation Screen Based on Organic Mn(II) Halide Hybrids toward Planar and Nonplanar X-Ray Imaging

The urgency for cost-effective, high-resolution, flexible X-ray imaging detectors is generating great demand for scintillators with low-temperature processability, high scintillation yield, and negligible afterglow. X-ray imaging materials are currently dominated by inorganic scintillators in the form of rigid films and bulk crystals, which have inherent limitations including high-temperature, complex synthesis, and considerable challenges toward advanced nonplanar imaging. Here, high-performance and flexible X-ray scintillators based on novel zero-dimensional (0D) (BTPP)₂MnX₄ (BTPP = benzyltriphenylphosphonium; X = Cl, Br) halides are reported. They emit bright green light originating from the ⁴T₁-⁶A₁ transition of Mn²⁺ under X-ray excitation. In particular, (BTPP)₂MnBr₄ single crystals exhibit excellent air- and radiation-stability, a high scintillation yield of 53 000 photons MeV⁻¹, a low detection limit of 89.9 nGy_air s⁻¹, and an ultralow afterglow comparable to commercial Bi₄Ge₃O₁₂ (BGO) single crystals. Moreover, the (BTPP)₂MnCl₄@polydimethylsiloxane (PDMS) flexible scintillation screens achieve a high spatial resolution of 14.1 lp mm⁻¹ and realize high-quality imaging results of nonplanar objects. This study demonstrates that the flexible scintillation screens based on low-dimensional Mn(II) hybrid halides have significant potential for low-dose and high-resolution X-ray imaging applications.     

Light emission efficiency and imaging performance of Y3Al5O12: Ce (YAG: Ce) powder screens under diagnostic radiology conditions

In this study Y₃Al₅O₁₂: Ce powder scintillator was evaluated for use in X-ray imaging detectors. This phosphor, also known as YAG: Ce scintillator or P-46 phosphor, is a non-hygroscopic, emitting green light with very short decay time. These properties are very attractive for X-ray imaging. Y₃Al₅O₁₂: Ce powder was used to prepare various test screens (33–166 mg/cm²). Absolute luminescence efficiency measurements were performed for various X-ray tube voltages (50–130 kVp). In addition parameters related to image quality such as the modulation transfer function and the detective quantum efficiency were examined. A theoretical model, describing radiation and light transfer, was employed to fit experimental data and to estimate values of optical parameters. Absolute efficiency was found to decrease with X-ray tube voltage. Highest efficiency was obtained for the 107 mg/cm² screen. Light attenuation coefficients were close to those of green emitting rare earth scintillators. At low spatial frequencies the detective quantum efficiency was high for the 107–166 mg/cm² screens. The light emission efficiency and imaging performance of Y₃Al₅O₁₂: Ce was not better than currently employed scintillators. However due to its very fast response and high spectral compatibility to optical sensors it may be considered for use in digital imaging detectors.     

丝阵Z箍缩1维X射线辐射功率分布的数据处理

 在丝阵Z箍缩实验中利用CCD记录X射线辐射功率的1维时空分布图像，对光纤传输效率、图像聚焦、MCP与CCD的耦合效率等因素造成的图像失真进行了处理，利用实验实测的单光纤点扩展图像和光传输效率曲线对辐射功率分布图像进行处理，并修正光纤传输效率以及MCP和CCD间耦合效率不均匀性的影响以还原X射线辐射功率的1维空间分布信息。处理后将图像沿空间积分获得了与X射线功率谱仪相吻合的X射线辐射功率脉冲波形，同时不同发次由两系统得到的X射线波形的前沿之间也表现出了良好的一致性。     

激光高能X射线成像中探测器表征与电子影响研究

基于激光尾场加速电子的高能X射线源具有高光子能量与小源尺寸的特点,在高空间分辨无损检测方面发挥着十分重要的作用.在X光机上测量了CsI针状闪烁屏、锗酸铋(BGO)闪烁阵列与DRZ闪烁屏的本征空间分辨率,并模拟了三类探测器对高能X射线的能量沉积响应,其中CsI针状闪烁屏的空间分辨率高达8.7 lp/mm.采用Ta转换靶产生的高能X射线开展透视照相,能够分辨最高面密度33.0 g/cm~2的两层客体结构.开展了X射线照相、X射线与电子混合照相以及电子照相三种情况的比对实验,在X射线产额不足或探测效率不够情况下采用X射线与电子混合透视照相的方案,以牺牲对比度为代价,能较大程度地提高图像信号强度.     

High‐perfomance Ce‐doped multicomponent garnet single crystalline film scintillators

We report for the first time the optimized content and excellent scintillation properties of single crystalline film (SCF) scintillators of multicomponent Gd_3–xLu_x Al_5–yGa_y O₁₂:Ce garnet compounds grown by liquid phase epitaxy (LPE) method. The Gd_1.5Lu_1.5Al_2.75Ga_2.25O₁₂:Ce and Gd₃Al_2.75–2Ga_2.25–3O₁₂:Ce SCF show the light yield (LY) comparable with that of high‐quality bulk crystal analogues of these garnets but faster scintillation decay and very low thermoluminescence in the above room temperature range. To our knowledge, these SCF possess the highest LY values ever obtained in LPE grown garnet SCF scintillators exceeding by at least 1.5–1.6 times the values previously reported for SCF scintillators.

     

Further performance tests of a picosecond X-ray and laser induced streak camera system with fast scintillation materials

A further performance test of a fluorescence lifetime spectroscopy system with 2D-photon counting based on a streak camera was carried out. This system offers three different excitation light sources. It includes a pulsable X-ray tube with 40 kV and a laser. A pulsed UV-LED has been installed for sample excitation. The table top measurement device has a temporal resolution down to 20 ps after deconvolution and fluorescence/scintillation decay times can be evaluated in a wavelength selectable range between 200 and 850 nm. Cesium fluoride, cesium chloride and cesium bromide as fast core-valence luminescence emitters with a relatively low light yield were used in the presented performance test. The easily manageable system is able to detect low light levels and to determine the decay times in agreement with literature in most instances. Beside mentioned scintillators PbCO₃, SrI₂ and Lu₂SiO₅:Ce as a high light yield material were also measured.     

Properties of Ce-activated alkali-lutetium double phosphate scintillators

The scintillation properties of Ce-activated alkali-lutetium double phosphate single crystals that vary with the alkali ion type and activation level are summarized and compared. The materials investigated here have been identified as fast and efficient scintillators for the detection of X-ray and γ radiation, and in case of Li₃Lu(PO₄)₂:Ce, for thermal neutron detection as well.     

Ce3+-doped crystalline garnet films – scintillation characterization using α-particle excitation

Scintillating properties of Ce³⁺-doped (Lu,Y) aluminum garnet single crystalline films (SCF) were investigated. Thin SCF films of thickness between 1 and 30 μm were grown by a liquid phase epitaxy (LPE) method in various fluxes. The α-particle excitation (mainly 5.4857 MeV line of ²⁴¹Am) of pulse height spectra is used to measure scintillation response of SCF, especially peak of those α-rays which are totally absorbed in the films. Detailed studies and evaluation of scintillation measurements of large sets of Ce³⁺-doped SCF (Lu,Y) aluminum garnets showed that at present time (i) YAG:Ce SCF have comparable scintillation properties as YAG:Ce single crystals, especially their N_phels photoelectron yields are the same while (ii) scintillation properties of LuAG:Ce SCF do not reach those of LuAG:Ce single crystal.     

Influence of Kr doping on neon soft X-rays emission in fast miniature plasma focus device

An investigation on the possibility of enhancement of soft X-ray (SXR) (900–1600 eV) emission from a fast miniature plasma focus (FMPF) device of 235 J (at 14 kV) storage energy through doping of operating gas was performed. Neon (Ne), the operating gaseous medium, was doped with krypton (Kr) in different volumetric ratios at various operating pressures ranging from 2 to 14 mbar. The 1% Kr doping increased the average optimum SXR emission efficiency from 0.47% to 0.6% without enhancing the hard X-ray (HXR) (>1600 eV) emission. The Kr doping influenced the major pinching characteristics such as focusing efficiency and time to pinch with consequential effect on X-ray emissions. Synchronous operation of the 4 pseudo-spark gap (PSG) switches was mandatory for efficient discharge current delivery to the electrodes. A drastic improvement in the pinching efficiency was obtained with replacement of old and worn out PSG switches with the new ones. Optical imaging of current sheath dynamics was performed using gated ICCD camera to verify the normal operation of the device after the PSGs replacement. A numerical simulation analysis on the 2 cm long stainless steel tapered anode, used in this study, was done to predict the maximum SXR emission efficiency and the peak operating gas pressure. An analysis on the amount of SXR fluence generated at the source position and the proportion of it reaching the target position is also reported.     

HL-2M 装置软 X 射线阵列系统前置放大器设计

系统地介绍了 HL-2M 装置上软 X 射线阵列系统的工程概念设计、组成部分、关键工艺和技术研制 等。根据 HL-2M 装置的特点(如高温烘烤,真空室空间不足等),在该系统前置放大器设计中采用了很低的失调电 压和超低的偏置电流的高速宽带放大电路来降低暗电流和噪声,使得系统适用于较长距离传输的光电前置放大场 合,从而首次实现了前置放大器外置于真空室的安装布局。该放大器将大大增强整套软 X 射线阵列系统在高温烘 烤条件下的可靠性。      

铈离子掺杂浓度对氯化镧(LaCl_3:Ce)闪烁晶体发光性能的影响

本文采用垂直Bridgman法,分别生长了未掺杂LaCl3和掺有不同浓度CeCl3的LaCl3闪烁晶体,并对它们的透光性质、发光性质和光衰减特性进行了测试和对比分析.发现未掺杂LaCl3晶体的吸收边位于215 nm附近,本征发射峰为405 nm,衰减时间在1μs以上.该发光属于纯氯化镧晶体的自陷激子发射,但随着CeCl3掺杂浓度的提高,源于自陷激子(STE)的本征发射强度逐渐降低,LaCl3:Ce晶体中的吸收边逐渐红移至300nm,由Ce3+中心所产生的5d→4f发射逐渐增强,其衰减时间加快至～20 ns.这种现象被解释为LaCl3晶格中的自陷激子向Ce3+离子发光中心的能量传递作用所致.     

Lu2Si2O7∶Ce纳米晶的溶胶-凝胶法合成和闪烁性能

采用溶胶-凝胶法制备了Lu2Si2O7∶Ce纳米晶,利用X射线衍射(XRD)、扫描电镜(SEM)、荧光光谱仪、X射线激发发射谱仪对制备的Lu2Si2O7∶Ce纳米晶的晶相结构、微观形貌和光学性能进行了表征。结果表明,溶胶-凝胶法制备的Lu2Si2O7∶Ce前驱体在煅烧温度为1000℃时开始晶化,晶粒尺寸随着煅烧温度的升高而变大,1200℃煅烧2 h后的晶体颗粒均匀,分散性最优,平均晶粒尺寸约为28.9 nm,呈近球形;Lu2Si2O7∶Ce纳米晶的紫外吸收谱存在峰位分别为304 nm和350 nm两个吸收峰,源自于Ce^3+离子的4f→5d跃迁;光致发射谱和X射线激发发射谱都表现为典型的非对称双峰结构,归属于Ce^3+离子的5d^1→2F5/2和5d^1→2F7/2跃迁,Ce^3+离子的最佳掺杂浓度约为1%;荧光衰减时间约为37.2 ns,可满足高时间分辨X射线探测需要。