Fig. 1. Schematic diagram of fluorescence excitation

Fig. 2. Basic structure and working principle of fluorescent optical fiber sensing system

Fig. 3. Detection principle of dissolved oxygen optical fiber sensor^[16].(a) Schematic diagram of evanescent wave generation; (b) schematic diagram of dissolved oxygen detection process; (c) schematic diagram of instrumental setup and flow cell design

Fig. 4. Schematic diagram of luminescence process of lanthanide metal ions^[26]

Fig. 5. Crystal structures^[27].(a) Crystal structure of EuNDC; (b) tetrahedral crystal structure; (c) octahedral crystal structure

Fig. 6. Upper: pH responsive DAOTA dyes 1a and 1b in protonated form and reference DMQA dye 2; bottom: with light emitting diode (LED) light source, optical fiber connector, photodiode/sensor point and optical fiber spectrometer detector^[40]

Fig. 7. Crystal structure and PXRD spectra^[44].(a) Crystal structure of Tb-MOF; (b) PXRD patterns of as-synthesized Eu_0.034Tb_0.966-NMOF and Eu_0.034Tb_0.966-NMOF soaked in water with pH values of 3.00 and 11.00, and simulated Tb-MOF from X-ray single structure

Fig. 8. Diagram of preparation process of CDs@UiO-66 (OH)₂ using solvent-free method^［47］

Fig. 9. Spatial topology and fluorescence emission spectra^[48].(a) Spatial topological structure of Zr-TCPBP; (b) fluorescence emission spectra of Zr-TCPBP in aqueous solution with pH of 1.10-6.70

Fig. 10. Schematic diagram of pH detection with LMOFl and γ-Fe₂O₃@LMOF1^[49]

Fig. 11. Schematic diagram of pH response of MOF/PC materials^[50]

Fig. 12. Scheme for synthesis of UIO-66-ONa by Schiff Base reaction^[63］