Term of Award

Spring 2016

Degree Name

Master of Science in Applied Physical Science (M.S.)

Document Type and Release Option

Thesis (open access)

Committee Chair

Xiao-Jun Wang

Committee Member 1

Li Ma

Committee Member 2

Marshall Ming

Abstract

In this work, the up-conversion (UC) emissions of Er3+ in a gadolinium tungstate host was investigated to analyze the possible processes of up-conversion by 1500 nm and 980 nm excitation. Studies were conducted to see how the 4S3/2 -> 4I15/2 transition changed with varying current through the excitation source, varying excitation wavelength, and doping concentration. Power dependent studies revealed that under 1500 nm excitation the 4S3/2 -> 4I15/2 transition needed 3 photons, while 980 nm excitation could do the same transition with 2 photons. It was found that 1500 nm could produce more efficient red emission due to the 4I9/2 -> 4I15/2 transition only needing 2 photons. Concentration dependence studies revealed many trends of how up-conversion processes varied with erbium ion separation. The number of photons used to UC 980 nm decreases as concentration increases, meaning that the mechanism depends on energy transfer UC and the inefficiency of green emissions at higher concentration is due to concentration quenching. UC of 1500 nm also uses less photons as concentration increases; red and green emissions are not as dependent on energy transfer UC as 980 nm UC. Also, as concentration increases past the point least photon use, the erbium ions start cross relaxing causing the number of photons used to increase rapidly. It was found that even after cross relaxation becomes the dominant UC process, the intensity still increases as concentration increases until a point where quenching starts to take effect.

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