Luminescence Cryothermometry, Year 1

The proposed effort makes innovative use of luminescence thermometry to provide temperature mapping of surfaces at cryogenic temperatures that cannot be obtained by conventional thermal imaging techniques because of insufficient thermal radiation for detection at these temperatures. Two classes of high temperature sensitivity phosphors will be investigated for cryogenic temperature mapping: (1) transition-metal doped oxides with energy level gap tailored for cryogenic temperature sensitivity and (2) quantum dot phosphors with particle sizes tailored for cryogenic temperature sensitivity. A strategic choice of transition metal -doped oxides with very small energy differences between two excited electron energy levels will provide the desired enhanced temperature sensitivity at very low temperatures. The quantum phosphor candidates will take advantage of very recent development of quantum dots as nanothermometers and will be selected according to particle sizes that give greatest sensitivity at very low temperature. The full field noncontact temperature measurements will provide much less intrusive and more coverage than the discrete temperature measurements on cryogenic tanks currently obtained by discrete thermocouples or resistance temperature detectors.

The research plan will be perform temperature calibrations from 77 K (ℓN2) to RT for thermographic phosphor candidates that include Cr-doped Ga₂O₃ particles and CdSe quantum dots that have been selected for high temperature sensitivity at cryogenic temperatures. Temperature calibrations will be performed for at least three phosphor candidates by 3/31/21. The temperatue precision of luminescence lifetime vs. peak intensity ratio temperature measurements will be compared for the phosphor candidates. Paint formulations and application methods will be developed for the best performing transition metal doped oxide phosphor and quantum dot phosphors by 5/31/21. A culminating heat leak detection demonstration will be performed on a painted cryogenic tank with an intentional internal flaw by 9/30/21. At the end of the proposed effort, arrangements will be made to incorporate the best performing cryogenic thermally sensitive paint into cryogenic tank testing in the SMiRF facility where it would be used to identify and quantify undesirable heat conduction paths that are currently difficult to evaluate.

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