Structure and Luminescence of Europium-Doped Gadolinia-Based Core/Multi-Shell Scintillation Nanoparticles
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1164-L11-01
Structure and Luminescence of Europium-Doped Gadolinia-Based Core/Multi-Shell Scintillation Nanoparticles Teng-Kuan Tseng, Jihun Choi and Paul H. Holloway Department of Materials Science and Engineering University of Florida, Gainesville, FL 32611-6400, USA
ABSTRACT Scintillating nanoparticles with a SiO2 core and a Gd2O3 shell doped with Eu3+ were synthesized with a sol-gel process. Based on transmission electron microscopy (TEM) data, a ~13 nm Gd2O3 shell was successfully coated onto ~220 nm mono-dispersed SiO2 nanocores. Eu3+ ions at concentrations of nominally 5 at% exhibited photoluminescent (PL) emission from the SiO2/Gd2O3 nanoparticles after being calcined at 800 0C for 2 h. The SiO2 remained amorphous after calcining, while the Gd2O3 crystallized to a cubic structure. The PL emission was from the 5D0-7F2 transitions of Eu3+ at 609 and 622 nm. Photoluminescence excitation (PLE) data showed that emission from Eu3+ could result from direct excitation, but was dominated by the oxygen to europium charge-transfer band (CTB) between 250 and 280 nm for Eu3+ doped in Gd2O3. The quantum yield (QY) from thin films drop cast from a mixture of 20 mg of calcined nanoparticles in 500 μL of polymethylmethacrylate (PMMA) and excited in the CTB was 20% for SiO2/Gd2O3:Eu3+ core/shell scintillation nanoparticles. Finally, the above core/shell nanoparticles were passivated with a shell of SiO2 to create e.g. SiO2/Gd2O3:Eu3+/SiO2 nanoparticles. The QYs for this nanostructure were lower than unpassivated nanoparticles which was attributed to a weak CTB for the amorphous SiO2 shell and a higher density of interface quenching sites.
INTRODUCTION Luminescent rare-earth nanocrystals and colloidal quantum dots incorporated with dopants have aroused great interests due to their applications in various fields, i.e. display and solid-state lightening, scintillator detector, and biologic diagnosis [1-4]. In recent years, core/shell nanomaterials also have been studied extensively because of their great versatility in applications such as being tuned for high catalytic activity, better stability in various environments, and controllable surface modification properties. There are a variety of examples of core/shell nanostructures possessing merits mentioned above, e.g. Au/SiO2, CdSe/SiO2, CdS/ZnS, and polypyrole/Fe2O3 [5-7]. For applications as scintillation detectors, the materials should possess the properties of being luminescent with short decay time, high atomic number and density, low afterglow, large light output and low hygroscopicity. Generally, the scintillation materials are made in the form of single crystal by elaborate single crystal growth methods, i.e. Czochralski or Bridgman growth methods. In this work, a sol-gel precipitation method will be employed to prepare SiO2/Gd2O3:Eu3+ and SiO2/Gd2O3:Eu3+/SiO2 core/multi-shell scintillation nanoparticles. Mono-dispersed spherical SiO2 nanoparticles were first prepared to serve as the template and Gd2O3 shell was deposited on the surfaces of SiO2. Europium doped Gd2O3
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