Masters Theses

Date of Award

5-1989

Degree Type

Thesis

Degree Name

Master of Science

Major

Electrical Engineering

Major Professor

Michael J. Roberts

Committee Members

Stephen W. Allison, Graham W. Hoffman

Abstract

Emission properties of fifteen different powder and crystalline thermographic phosphors have been characterized for potential use in high temperature sensing applications. Excitation and emission spectra of these rare-earth activated thermographic phosphors have been measured as a function of temperature using a special mini oven built inside of a fluorescence spectrophotometer. Several of the thermophosphors underwent decay lifetime analysis and were calibrated for use in high temperature measurements.

The excitation spectra taken from room temperature to approximately 400°C, reveal that the phosphors Y2O3:Eu3+, YV04:Eu3+, Ba3(P04)2:Eu2+, LaP04:Eu3+, LuP04: Eu3+, YP04:Eu3+, YV04:Dy3+, Y202S:Eu3+, and Y202S:Tb3+ exhibit a significant temperature-dependent shift in their charge-transfer (C-T) absorption band. In addition, the peak position of the charge-transfer band in the europium-doped orthophosphate crystals is located at higher energies or deeper into the ultraviolet as the cation radius of the host crystal lattice decreases. The experimental results also show that the onset quenching temperature of the orthophosphate phosphors increases as a function of decreasing cation radius. The orthophosphate crystals YP04:Eu3+, LuP04:Eu3+, and LuP04:Dy3+ were found to have high onset quenching temperatures when compared to those of the powder phosphors. Orthophosphate single-crystals may prove to be the phosphor of choice for high temperature measurements ranging from 700°C to 1400°C.

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