Semester of Graduation

Fall 2022

Degree

Master of Science in Chemical Engineering (MSChE)

Department

The Gordon A. and Mary Cain Department of Chemical Engineering

Document Type

Thesis

Abstract

Rare earth doped metal oxides are widely employed as phosphor materials for white light LEDs (w-LEDs). The aim of this work is to engineer anionic sites of metal oxides, specifically, Y2O3, to investigate structural and luminescent properties relationships and energy transfer mechanisms between rare earth sensitizer and activator ions in different hosts.

A low temperature two-step hydrothermal/combustion method was employed to incorporate sulfate ions into Y2O3. Furthermore, annealing at 600 °C under H2/N2 was employed to convert Y2O2SO4 to Y2O2S. XRD along with FTIR spectroscopy unveiled the formation of monoclinic and trigonal phase of Y2O2SO4 and Y2O2S, respectively. Furthermore, Eu3+ was used to relate structural properties to luminescent properties due to the hypersensitivity of Eu3+ to the local environment and its coordination with ligand. PLE and PL measurements revealed a red shift of the charge transfer band and electric dipole transitions of Eu3+ due to different hybridization and optical electronegativities between rare earth ions and SO42- and S2- ions. Additionally, thermal stability analysis with TGA/DSC confirmed that Y2O2SO4 transformed to Y2O2S starting at 600 °C and also some of the Y2O2SO4 decomposed to Y2O3 at 800 °C under H2/N2 flow.

Ultimately, after revealing the structure-property relationships and phase transitions, Tb3+ and Tb3+/Ce3+ doping were used to identify the best host material for efficient energy transfer. Room temperature PL measurements and time-resolved spectroscopy at cryogenic temperature (77 K) showed that, Y2O2SO4 is the most efficient host for realizing energy transfer from Ce3+ to Tb3+ to enhance green emission of Tb3+ ions owing to crystal field splitting of Ce3+ ions which occupied C1 symmetry sites. Overall, this work gives an idea of the impact of anionic substitutions on structural and photoluminescent properties of metal oxides in order to design better performing phosphor materials for the application of w-LED devices.

Date

10-31-2022

Committee Chair

Dr. Kerry M. Dooley

Available for download on Thursday, October 30, 2025

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