Abstract The optical limiting characteristics of the Cobalt (Co) metal-doped PVA films have been measured using two laser beams at 632.8 nm and 533 nm wavelength. Different weight percentages of Co metal were stirred with PVA solution to get polymeric composite films by casting method. The crystallinity degree and the intermolecular structure of the samples have been tested by X-ray diffraction (XRD) and FT-IR spectroscopy. The semi-crystalline order of the pure PVA reduced with more adding of Co-metal due to the interaction of dopant ions with one pair of electrons of oxygen in the hydroxyl (-OH) group of the matrix as confirmed by the FTIR spectra. Moreover, the formation of the Co clusters with different size and non-uniform distribution on the composite films surface morphology has been presented by SEM. The thermal stability was carried out via DTA (Differential thermal analysis) and revealed that the Co-metal/PVA composites are more stable than PVA pure. The doped PVA film absorption increased, while the absorption edge shifted from 5.33 eV to 4.61 eV with the Co metal ratio due to the formation of localized states in the forbidden gap during the interaction between the –OH groups in the matrix of PVA and Co-metals. Also, the Urbach energy of the present films has been estimated. The direct electronic transitions have been observed only at doping ≥7.5%, as established from the results obtained from Tauc's model and optical dielectric loss. The film with ten wt.% of Co-metal shows a small energy gap and significant absorption properties. Thus, the present polymeric composite films with high Co-metal concentrations are suitable for laser attenuation and optical limiting in photonic devices.

中文翻译：

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钴金属浓度对PVA微观结构和光学限制性能的影响

摘要 使用波长为 632.8 nm 和 533 nm 的两束激光束测量了钴 (Co) 金属掺杂 PVA 薄膜的光学极限特性。将不同重量百分比的 Co 金属与 PVA 溶液一起搅拌，通过浇铸法得到聚合物复合薄膜。通过X射线衍射（XRD）和FT-IR光谱测试了样品的结晶度和分子间结构。FTIR 光谱证实，由于掺杂离子与基体羟基 (-OH) 基团中一对氧电子的相互作用，纯 PVA 的半结晶顺序随着 Co-金属的添加而降低。此外，扫描电镜显示了复合膜表面形貌上不同尺寸和不均匀分布的Co簇的形成。热稳定性是通过 DTA（差热分析）进行的，结果表明 Co-metal/PVA 复合材料比纯 PVA 更稳定。掺杂的 PVA 薄膜吸收增加，而吸收边随着 Co 金属比从 5.33 eV 移动到 4.61 eV，这是由于 PVA 基体中的 -OH 基团与 Co-相互作用期间在禁带中形成局域态。金属。此外，还估计了当前薄膜的 Urbach 能量。直接电子跃迁仅在掺杂 ≥ 7.5% 时观察到，这是根据从 Tauc 模型和光学介电损耗获得的结果确定的。含有 10 wt.% Co-金属的薄膜显示出小的能隙和显着的吸收特性。因此，