Abstract

A method for constructing the spectral dependence of near-field maximum efficiency \(Q_{{nf}}^{{{\text{max}}}}\) on the surface of a spherical nanoparticle has been suggested. It has been shown that, for preset wavelength λ and a selected refractive index of the environment n, the dependences of near-field efficiency Q_nf on particle radius a had the form of smooth curves with a maximum. Therefore, with knowledge of a sufficient number of such curves, one can find both the values of \(Q_{{nf}}^{{{\text{max}}}}\)(λ, n) and corresponding radii of the particles a (\(Q_{{nf}}^{{{\text{max}}}}\)(λ, n)). The suggested approach has been used to construct spectral dependences \(Q_{{nf}}^{{{\text{max}}}}\)(λ) for gold nanoparticles in a homogeneous isotropic nonabsorbing medium (in the range of λ from 200 to 1950 nm). Air (n = 1.0), water (n = 1.33), and a model organic compound with n = 1.5 have been selected as typical media. It has been demonstrated that, from a practical point of view, the sections of curves \(Q_{{nf}}^{{{\text{max}}}}\)(λ) from ≅ 480 to 1950 nm are of particular interest. Within this range of wavelengths, the dependences of \(Q_{{nf}}^{{{\text{max}}}}\) on λ represent asymmetric resonant-type curves. Absolute values of \(Q_{{nf}}^{{{\text{max}}}}\)(λ), the positions of their maxima, and the half-widths of all the curves have been found. It has been shown that, with the increase of n, the positions of a maximum and a half-width of each curve have changed insignificantly, while the extreme values of \(Q_{{nf}}^{{{\text{max}}}}\) themselves have increased substantially. Regular patterns of the behavior of functions a (\(Q_{{nf}}^{{{\text{max}}}}\)(λ, n)) have been determined. In order to illustrate the possibilities of the developed approach, two physical phenomena based on the use of near-field electromagnetic fields of high intensity have been discussed. It has been demonstrated that, in both cases, there was a satisfactory agreement between the values of a(\(Q_{{nf}}^{{{\text{max}}}}\)(λ, n)) calculated by us and the experimentally determined values found in published works for the radii of gold spherical nanoparticles at which the observed action of the near-field was manifested to the maximum extent. Prospects for application of the suggested approach to study the spectral behavior of the maximum efficiency of extinction, scattering, and absorption efficiency of spherical nanoparticles have been discussed.

中文翻译：

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球形金纳米粒子的最大近场效率的光谱依赖性

摘要

已经提出了一种用于在球形纳米粒子的表面上构造近场最大效率\（Q _ {{{nf}} ^ {{{\ text {max}}}}} \）的光谱依赖性的方法。已经表明，对于预设波长λ和环境n的选定折射率，近场效率Q _nf对粒子半径a的依赖性具有最大的平滑曲线形式。因此，在知道了足够数量的此类曲线后，既可以找到\（Q _ {{nf}} ^ {{{{\ text {max}}}} \\）（λ，n）的值，又可以找到粒子a（\（Q _ {{nf}} ^ {{{{\ text {max}}}} \\）（λ，n））。建议的方法已用于构造均质各向同性非吸收性介质（在λ范围内）中的金纳米粒子的光谱依赖性\（Q _ {{{nf}} ^ {{{\ text {max}}}}} \）（λ）从200到1950 nm）。典型的介质是空气（n = 1.0），水（n = 1.33）和有机化合物模型n = 1.5。从实践的角度证明，从≅480到1950 nm的曲线\（Q _ {{nf}} ^ {{{\ text {max}}}} \）（λ）的截面为特别关注。在此波长范围内，\（Q _ {{nf}} ^ {{{text {max}}}} \\对λ的依赖关系表示非对称谐振型曲线。的绝对值\（Q _ {{{nf}} ^ {{{\ text {max}}}} \）（λ），最大值的位置以及所有曲线的半角宽度已找到。结果表明，随着n的增加，每条曲线的最大宽度和半宽度的位置变化不明显，而\（Q _ {{nf}} ^ {{\\ t​​ext {max }}}} \）本身已大幅增加。函数行为的规则模式a（\（Q _ {{nf}} ^ {{{\ text {max}}}} \）（λ，n））已确定。为了说明所开发方法的可能性，已经讨论了基于使用高强度近场电磁场的两种物理现象。已经证实的是，在这两种情况下，有值之间令人满意的协议一（\（Q _ {{NF}} ^ {{{\ {文本最大}}}} \）（λ，ñ））和我们在已发表的著作中找到的针对球形金纳米颗粒半径的实验确定的值，在该半径下最大程度地体现了近场的观察到的作用。讨论了应用该方法研究球形纳米粒子最大消光，散射和吸收效率的光谱行为的前景。