Characterization of Luminescent Materials for Application in the Space Environment

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Sanders, Michael H.
Sedwick, Raymond
The medium Earth orbital (MEO) altitudes are greatly underutilized due to the harsh radiation environment. In thinking of alternative ways to work in this environment, luminescent materials are proposed as a replacement or augmentation for power. An investigation into the radiation resilience of some luminescent materials for use in space was undertaken. The results have been integrated into a baseline design for utilizing such materials for power generation via luminescent solar concentrators (LSC) in the space environment. The performance of such a system is compared to that of existing solar cell based power generation. Rhodamine 6G, Fluorescein and Cytodiagnostics Large Stokes Shift 500 dye was used in the radiation experiments. Rhodamine 6G and Fluorescein were chosen due to their well-documented history, while Cytodiagnostics dye was selected to further characterize a non-traditional, potential luminophore. Concentrations of the luminescent materials were mixed with polymer host materials and dissolved in a solvent, then spin coated onto quartz substrates to produce thin film test samples. Absorption and emission measurements were taken and analyzed to determine the materials radiation tolerance. The results showed a good tolerance for Rhodamine 6G while the other materials did not perform as well. To enhance the understanding of the environmental constraints, a thermal simulation was performed to investigate the extreme operating temperatures, and how heating may affect the materials in the power generation system. An interesting trade caused by temperature effects was shown. The solar cell in the LSC system operates at a lower, more efficient temperature, but the luminophores become less efficient from solar heating. The end result is that the overall LSC system efficiency remains fairly constant as the system is heated.