Design of optical characteristics of ceria nanoparticles for applications including gas sensing and up-conversion

Shehata, Nader

Design of optical characteristics of ceria nanoparticles for applications including gas sensing and up-conversion

dc.contributor.author	Shehata, Nader	en
dc.contributor.committeechair	Meehan, Kathleen	en
dc.contributor.committeemember	Xu, Yong	en
dc.contributor.committeemember	Elosairy, Mohammad Ali Mahmoud	en
dc.contributor.committeemember	Heremans, Jean J.	en
dc.contributor.committeemember	Orlowski, Mariusz K.	en
dc.contributor.committeemember	Hudait, Mantu K.	en
dc.contributor.department	Electrical and Computer Engineering	en
dc.date.accessioned	2014-07-16T23:08:33Z	en
dc.date.available	2014-07-16T23:08:33Z	en
dc.date.issued	2012-12-13	en
dc.description.abstract	This thesis investigates the impact of doping on the optical and structural characteristics of cerium oxide (ceria) nanoparticles synthesized using chemical precipitation. The dopants selected are samarium and neodymium, which have positive association energy with oxygen vacancies in the ceria host, and negative association lanthanides, holmium and erbium, as well as two metal dopants, aluminum and iron. Characteristics measured are absorption and fluorescence spectra and the diameter and lattice parameter of ceria. Analysis of the characteristics indicates qualitatively that the dopant controls the O-vacancy concentration and the ratio of the two cerium ionization states: Ce+3 and Ce+4. A novel conclusion is proposed that the negative association lanthanide dopants can act as O-vacancies scavengers in ceria while the O-vacancy concentration increases in ceria doped with positive association lanthanide elements. Doped ceria nanoparticles are evaluated in two applications: dissolved oxygen (DO) sensing and up-conversion. In the first application, ceria doped with either Sm or Nd and ceria doped with aluminum have a strong correlation between the fluorescence quenching with the DO concentration in the aqueous solution in which the ceria nanoparticles are suspended. Stern-Volmer constants (KSV) of doped ceria are found to strongly depend upon the O-vacancy concentration and are larger than some of the fluorescent molecular probes currently used to measure DO. The KSV measured between 25-50oC is found to be significantly less temperature dependent as compared to the constants of commercially-available DO molecular probes. In the second application, up-conversion, ceria nanoparticles doped with erbium and an additional lanthanide, either Sm or Nd, are exposed to IR radiation at 780 nm. Visible emission is only observed after the nanoparticles are calcinated at high temperature, greatly diminishing the concentration of O-vacancies. It is concluded that O-vacancies do not play a dominant role in up-conversion, unlike that drawn for down-conversion, where the fluorescence intensity is strongly correlated with the O-vacancy concentration. Correlations between annealing temperatures, dopant, and dopant concentrations with the power dependence of up-conversion on the pump and the origin of the intensities of the visible emission are presented. These studies show the promise of doped ceria nanoparticles.	en
dc.description.degree	Ph. D.	en
dc.format.medium	ETD	en
dc.identifier.other	vt_gsexam:75	en
dc.identifier.uri	http://hdl.handle.net/10919/49574	en
dc.publisher	Virginia Tech	en
dc.rights	In Copyright	en
dc.rights.uri	http://rightsstatements.org/vocab/InC/1.0/	en
dc.subject	Ceria nanoparticles	en
dc.subject	lanthanide dopants	en
dc.subject	oxygen vacancies	en
dc.subject	fluorescence quenching	en
dc.subject	oxygen sensing	en
dc.subject	up-conversion	en
dc.title	Design of optical characteristics of ceria nanoparticles for applications including gas sensing and up-conversion	en
dc.type	Dissertation	en
thesis.degree.discipline	Electrical Engineering	en
thesis.degree.grantor	Virginia Polytechnic Institute and State University	en
thesis.degree.level	doctoral	en
thesis.degree.name	Ph. D.	en