Zaman Quaid, S Costa Jefferson, R J Barreto Arthur, F D F Araujo Jefferson, D Carlos Luís, N Carneiro Neto Albano, Cremona Marco, Ahmed Zubair, S Cruz André Felipe, P Souza Nadson Welkson, Q da Costa Karlo, Dmitriev Victor, Laurenzana Anna, Margheri Francesca, Del Rosso Tommaso
Department of Physics, Pontifícia Universidade Católica do Rio de Janeiro, Rua Marques de São Vicente, 22451-900 Rio de Janeiro, Brazil.
Department of Electrical Engineering, Federal University of Pará, Belém, 66075-110 Pará, Brazil.
Langmuir. 2021 Mar 23;37(11):3248-3260. doi: 10.1021/acs.langmuir.0c02862. Epub 2021 Mar 8.
An alternative approach to classical surface plasmon resonance spectroscopy is dielectric-loaded waveguide (DLWG) spectroscopy, widely used in the past decades to investigate bio-interaction kinetics. Despite their wide application, a successful and clear approach to use the DLWGs for the one-step simultaneous determination of both the thickness and refractive index of organic thin films is absent in the literature. We propose here, for the first time, an experimental protocol based on the multimodal nature of DLWGs to be followed in order to evaluate the optical constants and thickness of transparent thin films with a unique measurement. The proposed method is general and can be applied to every class of transparent organic materials, with a resolution and accuracy which depend on the nature of the external medium (gaseous or liquid), the geometrical characteristics of the DLWG, and the values of both the thickness and dielectric constant of the thin film. From the experimental point of view, the method is demonstrated in a nitrogen environment with an accuracy of about 3%, for the special case of electroluminescent thin films of Euβ-diketonate complexes, with an average thickness of about 20 nm. The high value of the refractive index measured for the thin film with the Eu(btfa)(t-bpete) complex was confirmed by the use of a spectroscopic model based on the Judd-Ofelt theory, in which the magnetic dipole transition D → F (Eu) for similar films containing Eu complexes is taken as a reference. The DLWGs are finally applied to control the refractive index changes of the organic thin films under UVA irradiation, with potential applications in dosimetry and monitoring light-induced transformation in organic thin films.
与传统表面等离子体共振光谱不同的另一种方法是介质加载波导（DLWG）光谱，在过去几十年中被广泛用于研究生物相互作用动力学。尽管其应用广泛，但文献中缺乏一种成功且清晰的方法来使用DLWG一步同时测定有机薄膜的厚度和折射率。我们首次在此提出一种基于DLWG多模态特性的实验方案，以便通过一次独特测量来评估透明薄膜的光学常数和厚度。所提出的方法具有通用性，可应用于各类透明有机材料，其分辨率和精度取决于外部介质（气态或液态）的性质、DLWG的几何特征以及薄膜的厚度和介电常数。从实验角度来看，该方法在氮气环境中针对平均厚度约为20 nm的铕β - 二酮配合物电致发光薄膜这一特殊情况进行了演示，精度约为3%。通过使用基于贾德 - 奥费尔特理论的光谱模型，证实了含有铕（btfa）（t - bpete）配合物的薄膜所测得的高折射率值，其中以含有铕配合物的类似薄膜中的磁偶极跃迁D→F（Eu）作为参考。DLWG最终被用于控制有机薄膜在UVA照射下的折射率变化，在剂量测定和监测有机薄膜中的光致转变方面具有潜在应用。
