Nonlinear-Optical Response in Zeolitic Imidazolate Framework Glass

Recently, metal-organic frameworks (MOFs) have been confirmed to be stable in a vitreous state, thus stimulating growing interest in the discovery of the physicochemical properties of these newly explored types of glasses. Herein, we examine the nonlinear-optical (NLO) response of Zn- and Zn-Co-based zeolitic imidazolate framework-62 (ZIF-62) glasses using an open-aperture Z-scan technique. We reveal that the Zn-ZIF-62 glass does not characterize a saturable absorption feature (1030 nm femtosecond laser) owing to its low optical absorption in the near-infrared (NIR) spectral region. In contrast, a NIR absorption band (1100 nm) has been observed in Zn-Co-ZIF-62 glass, which exhibits a strong NLO response with a high modulation depth of 63.85%. We attribute the observed NLO response to transient saturation of the ⁴T₁(⁴F) level of Co ions upon femtosecond laser excitation. The intriguing NLO properties of this MOF glass may enable potential applications in the photonics fields for sensing and optical modulation.