Fig. 1. UC luminescence mechanism of the Er³⁺/Yb³⁺

Fig. 2. Preparation process of the rare earth ion-doped tellurite glass

Fig. 3. Rare earth ion-doped tellurite glasses fabricated by melt-annealing method

Fig. 4. Process of manufacturing tellurite fiber by combining suction casting method and rotational casting method

Fig. 5. DTA curve of Er³⁺/Yb³⁺ co-doped TWNZN glass^[13]

Fig. 6. UC and NIR luminescence spectra of visible light region. (a) TZBE glass; (b) TZBEY glass^[20]

Fig. 7. Absorption spectrum of co-doped TPO glass in the range of 350‒2000 nm^[21]

Fig. 8. UC luminescence spectrum of TZLB glass excited at 980 nm; (a) Different Er³⁺ mole fractions; (b) different Yb³⁺ mole fractions

Fig. 9. Change curve of emission spectrum of TZLB glass with temperature

Fig. 10. Basic mechanism of rare earth ion glass and optical fiber optical temperature measurement^[34]

Fig. 11. Manufacturing method of temperature-sensitive optical fiber head^[35]

Fig. 12. Experimental setup for measuring brain and body temperature^[35]

Fig. 13. Schematic diagram of the integrated microsphere sensing structure^[37]

Fig. 14. Experiment setup for monitoring ammonia content in water^[37]

Fig. 15. Schematic diagram of the all-fiber temperature sensing system^[13]