Characteristics of chromium doped spinel crystals for a fiber-optic thermometer application

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Thermometer probe using the chromium doped spinel crystals, MgAl₂O₄: Cr³⁺, has been fabricated and the wavelength dependences of PL lifetime are evaluated as compared with those using ruby crystals. Lifetimes and temperature coefficients of the spinel crystals (τ=10 ms, 37 μs/K), which were typically 3 times larger than that of the ruby crystals (τ=4 ms, 10 μs/K), varied from 4.74 ms to 1.65 ms with wavelength from 667.5 nm to 780 nm.