Hydrothermal synthesis and characterization of the eulytite phase of bismuth germanium oxide powders
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Pin Yang Sandia National Laboratories, Albuquerque, New Mexico 87185-0958
Mark A. Rodriguez Sandia National Laboratories, Albuquerque, New Mexico 87185-1411
Bernadette A. Hernandez-Sanchez, Nelson S. Bell, Andrew Velazquez, and Bryan Kaehr Sandia National Laboratories, Advanced Materials Laboratory, Albuquerque, New Mexico 87106
Marlene Bencomo Sandia National Laboratories, Albuquerque, New Mexico 87185-0958
James J.M. Griego Sandia National Laboratories, Albuquerque, New Mexico 87185-1411
Patrick Doty Sandia National Laboratories, Livermore, California 94551-0969 (Received 18 February 2014; accepted 14 April 2014)
A simple hydrothermal route to the eulytite phase of bismuth germanium oxide (E-BGO: Bi4(GeO4)3) that required no post-processing has been developed. The E-BGO material was isolated from a mixture of bismuth nitrate pentahydrate and a slight excess of germanium oxide in water under hydrothermal conditions (185 °C for 24 h). The resultant materials were characterized by powder x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and luminescence measurements to verify the particle’s phase (eulytite), morphology, size, and response to a variety of excitation energy sources, respectively. Photoluminescence spectroscopic response from E-BGO pellets indicated that the samples exhibited a strong emission peak consistent with an x-ray induced luminescence of a E-BGO single crystal (500 nm excited at 285 nm). Cathodoluminescent properties of the E-BGO displayed a broadband spectrum with a maximum at 487 nm. The growth process was consistent with a standard Oswald ripening and LaMer growth processes.
I. INTRODUCTION
Since the first report of bismuth germanium oxide (Bi4Ge3O12 or BGO) as a scintillator in 1973, this material has slowly started to replace the ubiquitous thalliumdoped sodium iodide (NaI:Tl) in many of its applications.1,2 Some of the properties that have led to this substitution include the good stopping power of the high Z numbered Bi, high density (7.112 g/cm3), robust nature (hardness 5 Mho), air-stability (nonhygroscopic), radiation hardness (stable to 5.1 104 Gy), small afterglow (0.005% after 3 ms), rapid rise/decay time (high scintillation efficiency), good energy resolution (at 5–20 MeV), low self-absorption, photofraction, and a four times larger absorption coefficient.1–5 Even though scintillator BGO materials have only 20% of the light emission of NaI(Tl), a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.97 J. Mater. Res., Vol. 29, No. 10, May 28, 2014
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the maximum emission occurs at 480 nm and covers a wide range of wave lengths (375–650 nm) with a significant portion of the emission above 500 nm. While this may not be favorable for scintillation collection by photomultiplier tubes, this broad emission can be effectively collected by the new avalanche photodiode arrays.3 Furthermore, BGO single crystals produce ;8500 photons per 1 MeV of energy radia
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