2008 IEEE Nuclear Science Symposium Conference Record Scintillation Properties of a Crystal of (C 6 H s (CH2)2NH3)2PbBr4 Carel W.E. van Eijk, Member, IEEE, lohan T.M. de Haas, Piotr A. Rodnyi, Ivan V. Khodyuk, Kengo Shibuya, Fumihiko Nishikido, Masanori Koshimizu N69-3 Abstract- For the first time results obtained from gamma-ray excitation of a low-dimensional lead-halide-based perovskite- type organic-inorganic scintillator crystal are presented. Scintillation and luminescence properties have been studied of a 5 x 6 x 1 mm 3 single crystal of bis(phenethylammonium) tetrabromoplumbate(II), (C6H5(CH2)2NH3)2PbBr4. Excitation, emission, pulse-height and decay-time spectra are presented. The light yield is 10,000 photons per MeV, measured at 662 keV gamma-ray energy. The main decay time under pulsed x-ray excitation is 9.4 ns. Index Terms- Scintillation crystal, organic-inorganic hybrid compound, (C6H5(CH2)2NH3)2PbBr4, gamma-ray excitation, light yield, decay time. I. INTRODUCTION C E3+ doped materials have been in the centre of the search for novel efficient fast-response inorganic scintillators for a considerable time. Examples of commercialized results are YAI0 3 :Ce (YAP) [1], LU2SiOs:Ce (LSO) [2], and LaBr3:Ce [3]. A class of materials that has received less attention but is very promising considering its fast response times is that of low-dimensional semiconducting scintillators [4]. An interesting group is formed by the lead-halide-based perovskite-type organic-inorganic hybrid compounds. These self-assembling materials have a structure of alternating (PbX 4 )2- and organic ammonium layers (X is CI, Br, I). This two-dimensional (2D) system shows confinement in the direction perpendicular to the layers. Consequently the excitonic properties of the inorganic layer have been modified significantly. The exciton-binding energy has increased to --300 meV, i.e. it is an order of magnitude larger than the --30 meV of a bulk-type 3D semiconductor [5]. Therefore, the excitonic state in a 2D semiconductor is much more stable against temperature quenching. For 2D (C3H7NH3)2PbBr4, abbreviated C3PbBr4, the light yield is reduced by only a Manuscript received October 27, 2008. This work was partly supported by Japan Society for the Promotion of Sciences (KAKENHI, PO 18-538). C.W.E. van Eijk and J.T.M. de Haas are with the Faculty of Applied Sciences, Delft University of Technology, 2629 JB Delft, The Netherlands (e- mail: c.w.e.vaneijk@tudelft.nl). P.A. Rodnyi and I. V. Khodyuk are with the Faculty of Physics and Mechanics, St. Petersburg State Technical University, Polytekhnicheskaya 29, 195251 St. Petersburg, Russia (e-mail: rodnyi@tuexph.stu.neva.ru). K. Shibuya and F. Nishikido are with the Molecular Imaging Center, National Institute of Radiological Sciences, Anagawa 4-9-1, Inage-ku, Chiba 263-0024, Japan (e-mail: shibuken@nirs.go.jp). M. Koshimizu is with the Department of Applied Chemistry, Tohoku University, Aoba 07, Aramaki, Aoba-ku, Sendai 980-8579, Japan (e-mail: koshi@qpc.che.tohoku.ac.jp). factor of 4 when increasing the temperature from 25K to room temperature (RT), contrary to bulk-type (CH3NH3)PbBr3, for which the light yield is reduced by three orders of magnitude [6]. At RT a light yield of --3000 photons/MeV of absorbed proton energy was measured for C3PbBr4 [6]. For another 2D material, (C6H13NH3)2PbI4, abbreviated C 6 PbI 4 , a light yield of --5000 photons/MeV was observed [7]. Another consequence of the confinement is the increase of the exciton oscillator strength. This results in reduction of the decay time and, as competitive non-radiative decay processes will occur less, an increase of the light yield [4]. At RT a decay time component of 390 ps has been measured under pulsed electron excitation of C 6 PbI 4 [8]. C3PbBr4 shows a decay time component of2.8 ns [8]. These decay times are an order of magnitude faster than those of Ce 3 + doped scintillators [1 ]-[3], and in the case of C 6 PbI 4 the decay is even faster than that of core-valence luminescent materials [9]. For C 6 PbI 4 the intensity of the 390 ps component amounts 30% of the light yield of 5000 photons/MeV [8]. For C3PbBr4 the intensity of the 2.8 ns component is 400/0 of the light yield of 3000 photons/MeV [8]. These fast-response materials may become of great interest for the medical-diagnostics modality positron-emission tomography (PET). Inclusion of time-of-flight (TOF) information will improve the signal-to-noise ratio, and consequently the image quality, significantly [10]. Although the detection efficiency per unit scintillator length will be less for the typical densities of approximately 2.5 g/cm 3 of the organic/inorganic compounds, the possibly much improved TOF information may result in an overall gain. Studies on the applicability of LaBr3:Ce to PET are an example of this line of research [11]. Another application may be found in the field of security. There is a serious interest in the detection of fast neutrons from fissile materials, e.g. see [12], [13]. The large hydrogen content could make the short-decay-time organic/inorganic scintillator the constituent of a good fast- neutron detector. The measurements with protons on C 6 PbI 4 reported in [7] were performed on --250 nm films. In consequence of the self- assembling nature of these low-dimensional materials, it is relatively easy to make such thin layers by spin or dip coating. A study with the intention to exploit this is found in [14]. For x-ray imaging with sub-micrometer position resolution homogeneous thin scintillator screens are required. To study the feasibility of C 6 PbI 4 , x-ray excitation experiments were performed on < 1 Jlm layers of this material. For use in a gamma or fast-neutron detector scintillators of significant area and thickness are required. Of C 6 PbI 4 and C3PbBr4 single rystals were grown of respectively typically 7 x 978-1-4244-2715-4/08/$25.00 ©2008 IEEE 3525