Fig. 1. Crystal structures of ZIF-8 at different pressures^[37]. (a) At ambient pressure; (b) at 1.47 GPa

Fig. 2. SEM images of ZIF-67 prepared under different conditions^[52]. (a)--(d) Volume of methanol is 25, 100, 200, and 400 mL; (e)--(h) reaction time is 3, 30, 120, and 180 min; (i)--(l) stirring speed is 100, 400, 500, 1000 r/min

Fig. 3. Reorientation of imidazolate linkers in ZIF-8 makes it transfer from noncentrosymmetric to centrosymmetric, inducing an inversion center, so that the second harmonic generation is inactive ^[65]

Fig. 4. Typical TEM images and size distributions histograms of synthesized ZIFs^[66]. (a) ZIF-8; (b) Co20: Zn80 ZIF; (c) Co40: Zn60 ZIF; (d) Co60: Zn40 ZIF; (e) Co80: Zn20 ZIF; (f) ZIF-67

Fig. 5. Passively Q-switched Nd∶GdVO₄ lasers using ZIF-67 as saturable absorber^[67]. (a) 1 μm, output power; (b) 1 μm, pulse width and repetition rate; (c) 1 μm, typical pulse and steady pulse train (inset); (d) 1.34 μm, output power; (e) 1.34 μm, pulse width and repetition rate; (f) 1.34 μm, typical pulse and pulse train (inset)

Fig. 6. Nonlinear optical absorption of ZIF-67 ^[68]. (a)(b) Nonlinear transmittance; (c) reverse saturation absorption; (d) optical limiting phenomenon

Fig. 7. The performance of mid-infrared Q-switched laser with ZIF-67 saturable absorber ^[69]. (a) Pulse diagram and pulse sequence; (b) stability of output power at 3.3 W pumping power

Fig. 8. Third-order nonlinear susceptibility χ⁽³⁾ and nonlinear refractive index n₂ for ZIF-8 films with different thicknesses^[73]. (a) Third-order nonlinear susceptibility; (b) nonlinear refractive index

Fig. 9. Second harmonic generation intensity versus time and temperature for ZIF-8 PMMA composite material irradiated by laser with wavelength of 1047 nm and pulse width of 150 fs^[75]. (a) Second harmonic generation intensity versus time; (b) second harmonic generation intensity versus temperature

Fig. 10. Nonlinear optical properties of ZIF-62 with the excitation of 1030 nm femtosecond laser^[76]. (a) Open-aperture Z-scan curves; (b) nonlinear transmittance