Third-order nonlinear optical susceptibility of (Cu, Mn, Cd) doping zeolitic imidazolate framework-67 in the visible region

A set of metal–organic frameworks (MOFs), pure ZIF-67 and doped with transient metal ions (Cu, Mn, and Cd), were synthesized from Co(II) nitrate and 2-methylimidazole and completely characterized. The MOFs synthesis proceeded through a facile one-step strategy based on the aqueous solution at room temperature. The physical characterization of fabricated MOFs by FT-IR, XRD, TEM, and SEM techniques revealed a nano-crystalline structure that undergoes a negligible variation upon inserting impurities of Cu, Mn, and Cd ions. Considering the XRD pattern, values of 5.9%, 14.78%, 16.02%, and 16.40% were resulted for the crystallinity index of ZIF-67, Cu-ZIF-7, Mn-ZIF-67, and Cd-ZIF-67, respectively. The Eg for pure ZIF-67 and ZIF-67 doped with cations of Cu, Mn, and Cd was measured to be ∼3.22, 2.16, 1.96, and 1.95 eV, respectively. The nonlinear optical (NLO) features of synthesized samples were evaluated via the Z-scan method at 532 nm. The positive nonlinear refractive (NLR) index of samples demonstrated the self-defocusing effect. The nonlinear absorption coefficient (NLA) of samples dedicated to the two-photon absorption (TPA) effect. The crystallinity index, polarizability treatment, and the ionic radius of doped ions increase the NLO properties of ZIF-67.