ZIF-8 is a prototypical porous material in the family of zeolitic imidazolate frameworks, and its structural stability is of great significance for a wide range of practical applications. Here, the intrinsic and extrinsic structural and mechanical responses of nanosized ZIF-8 perturbed by high external pressure have been comparatively investigated based on our in situ Raman measurements in different pressure environments, accompanied by synchrotron X-ray diffraction measurements and results from previous reports. An improvement of both the chemical and crystallographic stability of ZIF-8, rather than an intrinsic quick deterioration, can be observed when penetrating guest molecules get into the pores. Spectral evidence demonstrates that the CC section of the imidazolate ring is an optimal interaction site for the penetrating methanol, water, and nitrogen molecules. We further find that water molecules can cleave Zn−N bonds to bring linker-associated defects to ZIF-8. When compressed in the nonpenetrating silicone oil as a pressure transmitting medium (PTM) or when no PTM is used, irreversibility is observed, while samples show a highly reversible transformation both in the short-range and long-range regions upon decompression from a partially or entirely amorphous state in penetrating PTM. Furthermore, the released samples transform to a dense bulk state in the absence of penetrating PTM instead of preserving the original nanosized particles when penetrating pressure transmitting fluids is present. Moreover, the compressible behavior of ZIF-8 varies and is found to be strongly influenced by the size and polarity of molecules in the pores. The present results indicate that the stability, compressibility, and reversibility of ZIF-8 under pressure are closely related to the pressure environments and the characteristics of the guest molecules in the PTM. Thus, this study sheds light on the available mechanical modifications and selectable applications of ZIF-8 as gas absorbents for the future.

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Ultrasensitive pressure-induced optical materials are of great importance owing to their potential applications in optical pressure sensors. However, the lack of outstanding pressure sensitivity, observable color evolution, and structure reliability limits their further development in both practical applications and luminescence theory. To overcome the above problems, an enlightening methodology is proposed to explore the high sensitivity and phase stability of hafnium silicate K2HfSi2O7 (KHSO) phosphor with a Khibinskite structure. By employing X-ray diffraction (XRD) Rietveld refinement, cryogenic spectroscopy, and ancillary calculations, information on Eu2+ ion occupation is completely obtained at atmospheric pressure. The remarkable pressure sensitivity (dλ/dP = 3.25 nm/GPa–1) and excellent phase stability up to 20 GPa, along with the reproducible color hue variation, exhibit unprecedented superiority when used in optical pressure sensors. These advantages can be assigned to the pressure-induced Eu2+-selective occupation and the unique properties of 5d–4f transition (Stokes shift, nephelauxetic effect, and intense crystal field strength), which are clearly proved by measuring the XRD patterns, Raman spectra, and Gaussian fitting spectra under compression and decompression processes. The excellent luminescence property manifests that KHSO/Eu2+ can be considered as a potential luminescent material for solid-state lighting and optical pressure sensors.

The individual iodine molecules in the channels of AlPO4-5 can be regarded as molecular probes to detect its structural collapse.