上海光源XAFS线站时间分辨X射线激发发光谱实验系统

Time-Resolved XEOL Experiment System on BL14W1 at SSRF

介绍了上海光源XAFS线站（BL14W1）的时间分辨X射线激发发光光谱（TRXEOL）实验系统。该系统基于时间相关单光子计数法的原理设计,以同步辐射光源的脉冲特性及其良好的时间结构为基础,通过集成定时系统、光谱仪系统和核电子学系统,在国内同步辐射装置上首次实现了TRXEOL实验方法。定时系统提供同步触发电脉冲,用来标志X射线脉冲打到样品上的时刻,同步精度约6ps,延时分辨率5ps;光谱仪经光电探测器把样品发光信号转换成电脉冲,核电子学系统对定时电脉冲和发光电脉冲之间的时间差进行统计分析,可得到样品的发光衰减曲线,再结合光谱仪的扫描控制和数据获取系统,可得到样品的TRXEOL光谱。利用该实验系统可以测量发光样品的普通XEOL光谱、发光衰减曲线和TRXEOL光谱。用ZnO纳米线样品,进行了实验验证。实验得到的普通XEOL光谱能够明显区分该样品在390和500nm处的两个发光中心;得到的发光衰减曲线能够区分小于2ns的快发光过程和200ns的慢发光过程;分别在0～1,2～200和0～200ns时间窗口内测量得到了ZnO纳米线样品的TRXEOL光谱,在这3个发光时间带内得到了对应的发光信息;ZnO纳米线样品发光衰减曲线快发光峰的半高宽约为0.5ns,证明了TRXEOL系统的最小时间分辨率小于1ns。该系统在国内同步辐射装置上提供了用于研究发光材料的TRXEOL实验方法,该方法与发光模式的XAFS方法相结合,可更深入的研究发光材料的发光行为。整个实验平台操作简便、工作稳定可靠,不仅为发光材料的研究提供了研究手段,还为进一步开展发光模式XAFS和TRXEOL成像等实验方法提供技术前提。

A novel time-resolved X-ray excited optical luminescence（TRXEOL）experiment system was developed for X ray absorption fine structure spectroscopy（XAFS）beamline at Shanghai Synchrotron Radiation Facility（SSRF）.The TRXEOL system is composed of three parts：timing system,spectrometer system and nuclear instrument module（NIM）system.These three systems were integrated to measure and record the optical luminescence from the sample excited by the synchrotron X-ray pulses,according to the time-correlated single photon counting methodology.It＇s the first time in the domestic synchrotron radiation facilities to achieve TRXEOL experiment using the synchrotron X-ray pulses and the time structure of the storage ring.In this work,a SSRF-self-developed timing system was used,which is based on the Field programmable Gate Array and the high-speed serial communication technology.The timing system can provide trigger pulse synchronized with the X-ray pulse.The timing jitter is about 6ps,and the timing delay resolution is 5ps.The NIM system is the core of the TRXEOL experiment system,it has three main modules：the Co nstant Fraction Discriminator（CFD）,the Time to Amplitude Converter（TAC）and the Multi-Channel Analyzer（MCA）.During one excitation circle,the spectrometer and the Photomultiplier Tube detector tra nslate the induced luminescence of the sample excited by a single X-ray pulse into electrical pulse.The CFD module eliminates the timing walk larger than 50 ps induced by the amplitude of the electrical pulse.The TAC module calculates the time interval between the timing trigger pulse and the luminescence electrical pulse,and converts the interval into proportional amplitude of voltage.After plenty of circles,the MCA module gets the luminescence decay curve by recording and analyzing the voltage signals.And the data acquisition system gets the TRXEOL spectra by scanning the spectrometer and acquiring the frequency of the voltage pulses from the TAC module.The TRXEOL experiment system hel ps researchers measure optical decay curves and spectra of the sample in different time windows.Many luminescence behaviors would be explained more deeply,together with the aid of the optical XAFS to get the electron structure of the sample.A sample of ZnO nanowire was studied using the TRXEOL system.The ordinary XEOL spectrum obtained could distinguish the 390 nm wavelength and the 500 nm wavelength luminescence center.The decay curve at 0nm wavelength could clearly show the fast luminescence process and the slow luminescence process.The full width at half maximum of the fast luminescence decay curve was about 0.5ns,showing that the minimum time resolution of the TRXEOL system is less than 1ns.The TRXEOL spectra obtained could respectively get the luminescence information within different time windows.It was demo nstrated that the TRXEOL system is not only feasible and reliable,but also supply XAFS beamline with the technical preparatio ns of time resolved techniques.