Optimization of Ce Content in Ce x La 1-x F 3 Colloidal Nanocrystals for Gamma Radiation Detection
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1164-L07-02
Optimization of Ce Content in CexLa1-xF3 Colloidal Nanocrystals for Gamma Radiation Detection Nathan J. Withers, Krishnaprasad Sankar, John B. Plumley, Brian A. Akins, Tosifa A. Memon, Antonio C. Rivera, Gennady A. Smolyakov, and Marek Osiński Center for High Technology Materials, University of New Mexico 1313 Goddard SE, Albuquerque, NM 87106-4343 Tel. (505) 272-7812; Fax (505) 272-7801; E-mail: [email protected] ABSTRACT We report on experimental investigations of CexLa1-xF3 colloidal nanocrystals (CNCs) and their properties in function of Ce content. The CNCs were characterized by TEM, energy-dispersive X-ray spectroscopy (EDS), steady-state UV-VIS optical absorption and photoluminescence (PL) spectroscopy, and by PL lifetime measurements. We also report on observations of scintillation from the cerium-doped lanthanum fluoride CNC material in experiments on radiation detection. INTRODUCTION Colloidal nanocrystals (CNCs) are particles with the dimensions on the scale of 5-50 nanometers across, synthesized by chemical processes. At these scales, the crystals exhibit enhanced quantum mechanical effects such as bandgap widening, decrease in carrier lifetime, and the dominance of surface effects. The chemical assembly of these materials is commonly known as “bottom up” nanotechnology, where self-assembly is used to create large quantities of nanoscale materials that would be prohibitively expensive to create using other techniques such as e-beam lithography. CNCs have attracted tremendous interest over the last few years for a wide range of biomedical, biochemical sensing, and optoelectronic applications [1-3]. For example, this technology is being researched to produce phosphors for light emitting diodes [3-4], markers for biological labeling [5], and photovoltaic devices [6]. Detection of nuclear radiation by its conversion to UV or visible light can be another attractive application of CNCs. The luminescence of lanthanide ions in organic media has been shown to greatly improve by doping them in the inorganic core of nanoparticles that are soluble in organic solvents [7]. This is due to the fact that the long-lived excited state of the lanthanide ions is quenched very effectively by the high-energy vibrations of closely spaced organic groups [8]. Since higher Ce content is expected to lead to increased self-absorption of Ce emission [9], an optimal concentration should exist that maximizes quantum efficiency at a fixed CNC concentration. Due to their small size, CNCs are expected to have better solubility in organic polymer or inorganic sol-gel host materials and to cause much less scattering, which should result in higher efficiency of the scintillator. There have been very few published preliminary studies of radiation response of nanocomposites based on CNCs. Lithiated (6LiOH) sol-gel doped with CdSe/ZnS QDs was considered as a potential neutron detector and tested under alpha irradiation [10]. Commercial CdSe/ZnS core-shell QDs were inserted in porous glass and exposed to alpha [11] and gamma [12
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