1. Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, China 2. University of Chinese Academy of Sciences, Beijing 100049, China
Abstract：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 6 ps, and the timing delay resolution is 5 ps. 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 0 nm 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 0.5 ns, showing that the minimum time resolution of the TRXEOL system is less than 1 ns. 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.
Key words：Time resolved spectroscopy;TRXEOL;Time-correlated single photon counting method
[1] Liu H, Zhou Y N, Jiang Z, et al. Journal of Synchrotron Radiation, 2012, 19: 969. [2] GU Jun-jun, WEI Xiang-jun, et al(顾俊俊，魏向军，等). Nuclear Techniques（核技术），2011，34（5）：341. [3] Yuan F, Song X, Xiangjun W, et al. Diamond Light Source Proceedings. 2011, e49: 5. [4] ZHANG Wen-zhi, LIU Gui-min, ZHAO Li-ying, et al(张文治，刘贵民，赵黎颖，等). Chinese Physics C, 2008, 32: 109. [5] Dennis M Mills. Third-Generation Hard X-ray Synchrotron Radiation Techniques. Wiley-Interscience Press, 2002. [6] Rosenberg R A, Sun X H, Sham T K, et al. Appl. Phys. Lett., 2006, 89: 093118. [7] Zhou X T, Sham T K, Wu Y, et al. Chem. Soc., 2007, 129: 1476. [8] Taylor R P, Finch A A, Mosselmans J F W, et al. Journal of Luminescence, 2013, 134: 49. [9] Tsun-Kong Sham, Richard A Rosenberg. Chem. Phys. Chem., 2007, 8: 2557. [10] Becker W. Advanced Time-Correlated Single Photon Counting Techniques(高级时间相关单光子计数技术). Beijing: Science Press(北京：科学出版社), 2009. [11] Rosenberg R A, Zhou X T, Sham T K, et al. Appl. Phys. Lett., 2005, 86, 263115(1-3). [12] Demas J N. Excited State Lifetime Measurements. New York: Academic Press Inc, 1967. [13] ZHAO Li-ying, YIN Chong-xian, LIU De-kang, et al(赵黎颖，殷重先，刘德康，等). Nuclear Techniques(核技术), 2006, 29(1): 1. [14] Liu M, Liu D K, et al. Proceedings of IPAC2013, 2013, 06(T24): 2992. [15] LIU Ming, YIN Chong-xian, ZHAO Li-ying，et al(刘 鸣, 殷重先，赵黎颖，等). Nuclear Techniques(核技术)，2010, 33(6): 425.
