Composite films with alternating layers (PAH/PSS)₃(AB/POM)_n (PAH = polyallylamine hydrochloride, PSS = polystyrene sulfonate) derived from Alcian Blue-tetrakis(methyl-pyridinium) chloride (abbreviated as AB) and Keggin type polyoxometalates (POM = H₄SiW₁₂O₄₀, H₃PW₁₂O₄₀, H₃PMo₁₂O₄₀, H₅PMo₁₀V₂O₄₀) have been fabricated and characterized. Under laser irradiation at 532 nm with a pulse duration of 6–7 ns, a repetition rate of 10 Hz and the intensity of the light at focus E₀ being 10 μJ, the composite films exhibit self-defocusing behavior and saturated absorption effects, and the nonlinear optical absorption coefficient β (m W⁻¹) and refractive index n₂ (m² W⁻¹) of the films are 4–5 times larger than those of pure AB solution in view of their magnitude. Interestingly, it is found that third-order NLO susceptibilities χ⁽³⁾ of films are in the order of χ⁽³⁾(AB/PSS) < χ⁽³⁾(AB/SiW₁₂) < χ⁽³⁾(AB/PW₁₂) < χ⁽³⁾(AB/PMo₁₂) < χ⁽³⁾(AB/PMo₁₀V₂), which is reversed to the order of E_LUMO(SiW₁₂) > E_LUMO(PW₁₂) > E_LUMO(PMo₁₂) > E_LUMO(PMo₁₀V₂), affirming that the incorporation of different Keggin type POMs of a lower LUMO energy level with phthalocyanine molecules into multilayers could tune the NLO responses of phthalocyanine films. It is concluded that the lower LUMO level of POM than that of the phthalocyanine can stimulate the easier transformation of excited electrons from AB to the POM within the donor–acceptor system (phthalocyanine molecules acted as an electron donor while POMs as an electron acceptor in the composite films) when flashed with the laser, which is thought to be accountable for the profound third-order optical nonlinearity of the composite films.

中文翻译：

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含阳离子酞菁和Keggin多金属氧酸盐的超薄膜的三阶NLO性能是通过从水溶液中逐层沉积制备的

具有交替层（PAH / PSS）₃（AB / POM）_n（PAH =聚烯丙胺盐酸盐，PSS =聚苯乙烯磺酸盐）的复合膜，其衍生自Alcian Blue-tetrakis（methyl-pyridinium）chloride（缩写为AB）和Keggin型多金属氧酸盐（ POM = H ₄ SiW ₁₂ O ₄₀，H ₃ PW ₁₂ O ₄₀，H ₃ PMo ₁₂ O ₄₀，H ₅ PMo ₁₀ V ₂ O ₄₀）已被制作和表征。在532 nm的激光辐照下，脉冲持续时间为6-7 ns，重复频率为10 Hz，焦点E ₀处的光强度为10μJ，复合膜表现出自散焦性能和饱和吸收效应，并且考虑到膜的大小，其非线性光学吸收系数β（m W ^-1）和折射率n ₂（m ² W ^-1）是纯AB溶液的4-5倍。有趣的是，发现薄膜的三阶NLO磁化率χ ^（3）约为χ ^（3）（AB / PSS）<χ ^（3）（AB / SiW ₁₂）< χ ^（3）（AB / PW ₁₂）< χ ^（3）（AB / PMo ₁₂）< χ ^（3）（AB / PMo ₁₀ V ₂）E _LUMO（SiW ₁₂）> E _LUMO（PW ₁₂）> E _LUMO（PMo ₁₂）> E _LUMO（PMo ₁₀ V ₂的顺序），确认将具有较低LUMO能级的不同Keggin型POM与酞菁分子结合到多层中可以调节酞菁薄膜的NLO响应。结论是，POMO的LUMO含量低于酞菁的LUMO含量可以刺激受激电子在供体-受体体系中从AB转变为POM（酞菁分子充当电子供体，而POMs充当电子供体）。复合薄膜）在用激光闪光时被认为是造成复合薄膜深层的三阶光学非线性的原因。