Temperature sensor based on luminescence intensity ratio or whispering gallery modes in phosphate glass co-doped with Pr3+ and Yb3+
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Microspheres of diameters ranging from 30 μm to 100 μm, obtained from 0.1Pr3+-0.5Yb3+ codoped phosphate glass were fabricated and calibrated as optical temperature sensor. When the microspheres where pumped under 457 nm laser excitation, Pr3+ typical emission was observed as well as emission due to a Down Conversion (DC) process from Pr3+ to Yb3+ ions. Furthermore, whispering gallery modes (WGM) peaks superimposed to the Pr3+ and DC emission bands were observed. The microsphere was calibrated as a function of temperature using the intensity ratio of the 925 and 875 nm Pr3+ bands and the spectral red-shift from the WGM. Temperature uncertainty was obtained from both techniques obtaining values of 0.7 K and 0.4 K for the band ratio and WGM results, respectively.