Date of Award

2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Environmental Science

First Advisor

Assefa, Zerihun

Abstract

This study reports the synthesis, characterization, and photoluminescence properties of a calcium tungstate/molybdate (CaWO4/MoO4) system, and the synthetic attempts of an agrellite (NaCa2Si4O10F) system. The objective is to modify the photoluminescence of both systems by doping with lanthanide/transition metal ions, and to convert them into phosphors with specific applications for light-emitting-diodes (LEDs). CaWO4 is used as a host matrix to fabricate a white light phosphor. When MoO4 is added to the system, its excitation range is extended, and its emission profile can be tuned by changing excitation wavelength. The simultaneous inclusion of Tm3+, Tb3+, and Eu3+ ions results in the phosphor emitting several hues of white light tunable by varying the excitation wavelength. Additionally, a comparison study of CaWO4 doped with Eu3+ showed that the inclusion of Na+ enhances the red emission of Eu3+, allowing the phosphor to emit ratios of blue and red light that are also tunable by excitation wavelength. The overall emission profile of the phosphor resembles the absorption profile of chlorophyll, allowing for potential utilization in a blue/red-emitting LED for plant growth. The photoluminescence of natural agrellite is scarcely found in the literature and has been reported here. Moreover, an attempt to synthesize the system by traditional sol-gel techniques and to replicate its pink emission was executed by using Ce3+, Mn2+, Dy3+, and Sm3+ dopants. The synthetic phosphor was found to crystallize in a phase different from agrellite, but triply-doping it with Ce3+, Tb3+, and Mn2+ produced a novel white light-emitting phosphor with potential applications for white-LEDs.

Download

Share

COinS