Structural\nComparisons, Fluorescence Properties, and\nGlass-to-Crystal Transformations of Heat–Cooled and Melt-Quenched\nZeolitic Imidazolate Framework Glass

As a representative of zeolitic imidazolate framework\nglass, agZIF-62\nhas been reported to be synthesized using a melt-quenching method\nin which the ZIF-62 crystal is heated to a temperature above the melting\npoint. Interestingly, we unexpectedly found that agZIF-62 can also\nbe synthesized by simple heating at temperatures lower than the melting\npoint, which may be assisted by the release of encapsulated solvent\nmolecules. The structural differences between melt-quenched agZIF-62\n(MQ-agZIF-62) and heat-cooled agZIF-62 (HC-agZIF-62) were investigated.\nThe results indicated that MQ-agZIF-62 is closer to the liquid state,\nwhile HC-agZIF-62 is closer to the crystal state. Interestingly, their\nluminescent emissions exhibit significant differences. Compared with\nthe ZIF-62 crystal, MQ-agZIF-62 showed a blue-shift of 14 nm, whereas\nHC-agZIF-62 showed a red-shift of 9 nm. The emission intensity of\nagZIF-62 is also significantly stronger than that of ZIF-62; thus,\nrapid semiquantitative detection of the content of the MOF glass in\nglass and crystal mixtures can be achieved. In addition, HC-agZIF-62\nand MQ-agZIF-62 can transform into ZIF-62 crystals via a solvent-media\nmechanism. This study provides new insights into ZIF-62 glass.