Polyoxometalates with tunable third-order nonlinear optical and superbroadband optical limiting properties

Abstract

In order to tune the intrinsic third-order nonlinear optical (NLO) properties of polyoxometalates (POMs), we adopted a strategy of substituting addenda atoms of POMs to obtain a class of polyoxomolybdovanadates, [TBA]₃[VMo₅O₁₉] (V₁Mo₅), [TBA]₄[V₈Mo₂O₂₈]·2CH₃CN (V₈Mo₂) and [TBA]₄[HV₉MoO₂₈]·2CH₃CN (V₉Mo₁) (TBA = tetrabutylammonium). Their structures were determined by single crystal X-ray diffraction and further characterized by FT-IR, Raman, UV-vis, diffuse reflection, HR MS, XPS, ICP-MS, CHN analysis and so on. The Z-scan curves of all compounds in a suspension of propanetriol demonstrate typical nonlinear absorption (NLA) irradiated by a laser at 532 nm and 1064 nm, which can be tuned by the substitution of addenda atoms in POMs. Among those, V₉Mo₁ possesses the smallest transmittance and largest nonlinear absorption coefficient. V₉Mo₁-doped organically modified silica (ORMOSIL) gel glasses have NLA and optical limiting (OL) properties that could be tuned by changing the doping concentration of V₉Mo₁. In particular, V₉Mo₁ exhibits an unusual superbroadband OL performance in the visible and long-wavelength near-infrared regions (532–2150 nm). To the best of our knowledge, this is the first example of a superbroadband optical limiter based on crystalline metal cluster compounds. Our current work not only provides a series of polyoxomolybdovanadates and V₉Mo₁-doped gel glasses with tunable third-order NLO properties and superbroadband OL performance but also affords a feasible strategy to tune the third-order NLO properties of POMs via the substitution of addenda atoms.