Localized Resonances of Composite Particles

Composite particles (CPs) formed by a homogeneous distribution of much smaller constituent metal nanoparticles (MNPs) in a host dielectric can be designed to exhibit two physically different types of resonances: (1) remarkably sharp localized surface plasmon resonances (LSPRs) and (2) equally narrow and strong localized dielectric resonances (LDRs). Preliminary results for spherical CPs show that the line width (fwhm) of both types of resonances can be as narrow as 100 meV. The values of fwhm are smaller than for spherical MNPs of the same size and comparable to the smallest reported values in isolated MNPs of arbitrary shape. LDRs call be tuned over a broad range of almost 1 mu m, for instance, from below 650 nm up to telecommunication bands above 1450 nm, by mere adjustment of the volume filling fraction of the constituent MNPs. The tunability of the LSPRs, which can also be designed to lie within the "biological window" of high optical transmission in blood and tissue between 700 and 1100 nm, is an order of magnitude smaller and amounts to similar to 100 nm. The sensing potential of the LSPRs of spherical CPs is also promising and is quantified by a figure of merit of 1.3. In the case of LSPRs, the dielectric constant of the host dielectric is required to be preferably at least 4, whereas pronounced LDRs can be observed already when the dielectric constant of the host dielectric is as small as 2. The Peculiar properties of the localized resonances of CPs have a potential for a variety of applications.