Interface State Assisted Ultrafast Carrier Dynamics in Core–Shell Structure ZIF-8@ZIF-67

Abstract

The role of the electronic state in metal–organic frameworks (MOFs) is crucial in various fields, such as optics, photocatalysis, electrochemical energy storage, and biomedicine. In the present work, ultrafast carrier dynamics in ZIF-67 and core–shell ZIF-8@ZIF-67 have been systematically studied by femtosecond transient absorption spectroscopy. Both ZIF-67 and ZIF-8@ZIF-67 exhibited remarkable broadband transient absorption responses in the range 800–1200 nm. Furthermore, the blue-shift of the photobleaching valley with increasing delay time of the probe laser was observed in ZIF-67 and ZIF-8@ZIF-67 due to the band gap renormalization effect. In addition, ZIF-8@ZIF-67, which had a core–shell structure, exhibited a higher carrier density and faster charge transfer rate compared to pure ZIF-67. This indicated that the interaction between core layer ZIF-8 and shell layer ZIF-67 formed an interface state that assisted the transfer of ultrafast carriers. The intermediate state energy level provided a convenient channel for the carrier transition and effectively promoted electron transfer and photogenerated carrier recombination. This work facilitated further revealing of ultrafast photoinduced carrier dynamics in MOFs and proposed a strategy to optimize the electron transition rate of materials by constructing core–shell structures, which had a guiding role in improving the performance of optoelectronic devices constructed from MOF materials.