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Synthesis and characterization of cerium-doped lanthanum halide colloidal nanocrystals


Please use this identifier to cite or link to this item: http://hdl.handle.net/1928/7642

Synthesis and characterization of cerium-doped lanthanum halide colloidal nanocrystals

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Title: Synthesis and characterization of cerium-doped lanthanum halide colloidal nanocrystals
Author: Sankar, Krishnaprasad
Advisor(s): Osinski, Marek
Committee Member(s): Krishna, Sanjay
Balakrishnan, Ganesh
Department: University of New Mexico. Dept. of Electrical and Computer Engineering
Subject: Nanocrystals
Lanthanum bromide
Lanthanum fluoride
LC Subject(s): Colloidal crystals
Degree Level: Masters
Abstract: Cerium-doped bulk lanthanum halide compounds are attractive in the field of high-energy radiation detection due to their interesting properties that include efficient radiation absorption, highly luminescent activator (cerium) emission through atomic transitions, host lattice protecting activators to prevent luminescence quenching, and fast decay-time radiative transitions between cerium levels. Cerium-doped bulk lanthanum bromide is reported to have a light yield of 60,000 photons/MeV, 2.5% full-width-to-half-maximum energy resolution (variation in emission light yield to absorbed gamma energy) for 662 keV gamma rays, 25 ns short decay time, and a density of 5.3 g/cm3 with 22 mm attenuation length for 511 keV gamma rays. However, the crystals are hygroscopic and hence have to be protected from external environment both during growth and use. Deriving the motivation from this material, this work strives at successful synthesis of stable cerium-doped lanthanum bromide/undoped lanthanum fluoride core/shell nanocrystals through inexpensive and repeatable colloidal routes. Following a systematic approach, cerium-doped lanthanum fluoride colloidal nanocrystals were synthesized through water-based and water-free (anhydrous) routes. Furthermore, core/shell synthesis of cerium-doped lanthanum fluoride/undoped lanthanum fluoride nanocrystals was achieved through the anhydrous route. The optimum cerium concentration (x) was empirically identified in the CexLa1-xF3 nanocrystal system in terms of light output from the activator levels of cerium. The persistence to high energy ionizing radiation was tested with a monoenergetic 137Cs gamma source. Cerium-doped lanthanum fluoride nanocrystals were tested in comparison with CdSe/ZnS nanocrystals. Then, using the indigenously developed anhydrous synthesis procedure in methanol, core/shell nanocrystals of cerium-doped lanthanum bromide/undoped lanthanum fluoride were successfully synthesized. All samples were subject to basic structural and optical characterization that included imaging using transmission electron microscope, energy dispersive spectroscopy, absorption measurements, excitation and emission photoluminescence spectroscopy, and photoluminescence lifetime measurements.
Graduation Date: December 2008
URI: http://hdl.handle.net/1928/7642

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