Visible Mie resonances in dielectric hollow spheres: Principle, regulation, and applications

Abstract

Dielectric nanostructures have recently been frequently employed as building blocks for photonic structures due to their advantages, including low energy dissipation, good chemical stability, and distinct resonant properties compared to plasmonic nanostructures. One of the most important principles that governs the optical property of dielectric nanoparticles is Mie resonance, which highly depends on dielectric property, size, morphology, and assembly structures of the nanoparticles as well as the surrounding environment. Among diverse types of Mie‐resonant nanoparticles, hollow spheres are particularly attractive as they can reduce multiple scattering and elongates the mean free path of the light passing through, which results in enhanced Mie resonance compared to solid particles and benefits a broad range of applications including structural color and beyond. This article aims at reviewing the recent development of Mie‐resonant hollow spheres from aspects starting from a brief theoretical introduction of Mie resonance in hollow spheres, principles for regulation of the resonances, followed by common strategies for synthesis, and recent advances in applications of Mie‐resonant hollow spheres. Remarks on the challenges and future opportunities in this area will also be presented.

Architecture Dictates the Activity of Hollow TiO2 Nanospheres in Photocatalytic Solar Energy Conversion

“…The resonances at modes 3, 4, 5, and 6 are observed, respectively, at λ = 563, 483, 431, and 396 nm. The scattering intensity is larger for the THSI-4 particle than for the THSI-1, which can be explained by the increase in shell thickness, as WGM propagates only within TiO 2 of large size . Interestingly, WGMs are attenuated in the UV region (Figure c,d), and in particular, scattering is nearly extinct for THSI-1, which is one of the most active photocatalysts.…”

“…The scattering intensity is larger for the THSI-4 particle than for the THSI-1, which can be explained by the increase in shell thickness, as WGM propagates only within TiO 2 of large size. 24 Interestingly, WGMs are attenuated in the UV region (Figure 6c,d), and in particular, scattering is nearly extinct for THSI-1, which is one of the most active photocatalysts. This result indicates that WGM, which is only dominant in the visible range, does not play a preeminent role in the photocatalytic activity of TiO 2 catalyst.…”

“…For example, Lien et al have prepared ZnO hollow spheres and demonstrated that WGM concentrates light at the surface of the hollow sphere, resulting in a greater responsivity in a photodetector device. Other advantages that have been invoked to account for the high photocatalytic activity of hollow structures include a large surface area, a fast mass transfer, and a small mean diffusion path for the photocarriers. − Interestingly, it is known that Mie-resonances become more intense when the thickness of the hollow sphere as well as their diameter increase, so one would expect that thickness to play a significant role in the regulation of the photocatalytic activity, with greater thicknesses and particle sizes leading to greater photocatalytic activity. Experimentally, it has been observed in the case of TiO 2 that smaller particle diameters actually lead to greater photocatalytic activity for the photodegradation of dyes, , in contradiction with what is expected from the contribution of light absorption.…”

“…WGM resonances are specific light propagation modes occurring in spherical structures. Currently, researchers have investigated the Mie scattering of TiO 2 hollow spheres with different sizes. , However, to our knowledge, no reports have investigated the effect of WGM resonances in TiO 2 hollow spheres and yolk–shell nanospheres. Our study’s inception was rooted in exploring WGM in hollow and yolk–shell nanospheres.…”

Hydrochromic Nanocapsule with Real Time Visual In Situ Water Level Sensing Function and Toughening Effect for Plastic Materials

“…On the other hand, nanoparticles have been intensively studied as fillers in a variety of polymeric materials, in order to obtain composite materials with improved mechanical properties. [ 11 ] However, while stimuli‐responsive nanoparticles with carefully designed structures and payload have found innovative applications in photonic structures, [ 12 ] controlled drug delivery, [ 13 ] antitumor therapy, [ 14 ] catalysis, [ 15 ] etc., [ 16 ] the design and application of responsive nanoparticles as smart nanofillers in polymer matrixes, which have additional functionalities other than mechanical enhancement, is still sparse. A few pioneer works have been reported.…”