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We report the study of light absorption efficiency of a hollow spherical microparticle (microcapsule) doped with strongly absorbing gold nanoparticles of spherical and cylindrical spatial shapes. By means of the FDTD numerical simulations, the absorption spectra of a doped microcapsule in the visible and near-IR spectral regions (from 0.5 μm to 0.9 μm) are calculated. Based on the research results we can draw the several conclusions. First, the absorption efficiency of initially transparent spherical microcapsule is effectively tailored by doping the necessary amount of strongly absorbing nanometersized metal (gold) particles. Meanwhile, with a rather low volume fraction of nano-inclusions in the capsule shell (~ 18%) it is possible to rise its absorption cross-section to the value of an absolutely absorbing sphere. Next, the spectral absorption of a microcapsule turns out to be quite non-uniform in the considered wavelength range of incident radiation and depends on the morphology of nano-inclusions. In some spectral regions, substantial capsule absorption enhancement is realized due to the resonant excitation of surface plasmons in nanoparticles (from 540 nm to 570 nm for spheres, from 670 nm to 770 nm for rods of various form factors). In the long-wavelength wing of the spectrum, the efficiency of absorption of a nanoparticle-doped capsule as a rule decreases due to its Mie-parameter decrease and a drop in the absorption coefficient of bulk gold. The chromatic dispersion of microcapsule absorption decreases with the increasing of volume content of plasmonic nanoparticles. By simultaneous combining gold nanoparticles of various shapes (spheres and rods), it is possible to obtain a quasi-neutral absorption of composite capsule in the considered wavelength range. Finally, the absorptivity of a nanoparticle-doped microcapsule can be calculated using the effective homogenized medium formulae mainly in the conditions of weak chromatic dispersion of capsule absorption. This situation is usually realized with cylinder-shaped nano-inclusions or at high levels of total shell absorption. Besides, the Bruggeman mixing rule does not capture the surface plasmon resonances of nanoparticle-dope.
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