Structure and Luminescence of Ce-doped Lu2SiO5 Nanophosphor
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Structure and Luminescence of Ce-doped Lu2SiO5 Nanophosphor Michael Wayne Blair1, Luiz G Jacobsohn2, Bryan L Bennett2, Ross E Muenchausen2, Stephanie C Sitarz2, James F Smith2, D Wayne Cooke2, Peter A Crozier3, and Ruigang Wang3 1 Earth and Environmental Sciences, Los Alamos National Laboratory, MS J495, Los Alamos, NM, 87544 2 Materials Science and Technology, Los Alamos National Laboratory, MS E546, Los Alamos, NM, 87545 3 School of Materials, Arizona State University, Tempe, AZ, 85287 ABSTRACT Nanophosphors correspond to nanostructured inorganic insulator materials that emit light under particle or electromagnetic radiation excitation. In this work we investigate the structure and luminescent properties of Ce-doped Lu2SiO5 (LSO) nanophosphors prepared by solution combustion synthesis with the Ce content 0.1 to 12 at. %. Samples were characterized by transmission electron microscopy (TEM), line scan electron energy-loss spectroscopy (EELS), xray diffraction (XRD), and electron paramagnetic resonance (EPR) spectroscopy. Photoluminescence excitation and emission spectra are composed of two major bands centered at 360 and 430 nm, respectively. These results reveal a red-shift and enhanced Stokes shift for the nanophosphors when compared to bulk. Ce content was also found to affect photoluminescence emission intensity and fluorescent lifetime. The nanophosphor concentration quenching curve presents a broad maximum centered at 1 at.%. Lifetime measurements show a continuous decrease from 34 to 21 ns as Ce content is increased. INTRODUCTION While an intense investigative effort on the optical properties of nanostructured semiconductors has been carried out for more than a decade, nanophosphors have remained largely unexplored until recently [1]. Of particular interest is the synthesis and characterization of rare-earth (RE) doped nanophosphors with emphasis on optical properties and how these change with reduced dimensionality. Since phosphors play an integral role in modern life, with applications ranging from fluorescent lighting and cathode ray tube displays to medical imaging (i.e., positron emission tomography scanners) and nuclear radiation detectors [2], it is very important to investigate the optical properties of oxyorthosilicates, including Ce-doped Lu2SiO5 (LSO). In luminescent materials, the electronic and optical properties of the luminescent centers are affected by the local symmetry, crystalline structure, degree of structural disorder, defects and chemical composition. In addition, the presence of other dopants/impurities can alter energy transfer processes. In nanophosphors, myriad surface effects are possible related to structural relaxation, reconstruction, dangling bonds, aging, etc, that arise from the high surface-to-volume ratio of nanoparticles. In this paper, we first examine how the structural properties of Ce-doped Lu2SiO5 (LSO) nanophosphors differ from the bulk samples. Then, we focus on the unique luminescence properties of nanophosphor LSO that arise largely from the structur
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