Effect of nanoshell geometries, sizes, and quantum emitter parameters on the sensitivity of plasmon-exciton hybrid nanoshells for sensing application

Abstract

A proposed nanosensor based on hybrid nanoshells consisting of a core of metal nanoparticles and a coating of molecules is simulated by plasmon-exciton coupling in semi classical approach. We study the interaction of electromagnetic radiation with multilevel atoms in a way that takes into account both the spatial and the temporal dependence of the local fields. Our approach has a wide range of applications, from the description of pulse propagation in two-level media to the elaborate simulation of optoelectronic devices, including sensors. We have numerically solved the corresponding system of coupled Maxwell-Liouville equations using finite difference time domain (FDTD) method for different geometries. Plasmon-exciton hybrid nanoshells with different geometries are designed and simulated, which shows more sensitive to environment refractive index (RI) than nanosensor based on localized surface plasmon. The effects of nanoshell geometries, sizes, and quantum emitter parameters on the sensitivity of nanosensors to changes in the RI of the environment were investigated. It was found that the cone-like nanoshell with a silver core and quantum emitter shell had the highest sensitivity. The tapered shape of the cone like nanoshell leads to a higher density of plasmonic excitations at the tapered end of the nanoshell. Under specific conditions, two sharp, deep LSPR peaks were evident in the scattering data. These distinguishing features are valuable as signatures in nanosensors requiring fast, noninvasive response.

Figure 1

Simulation space for calculating the scattering cross section of (a) spherical nanoshell, (b) elliptical nanoshell, (c) rod nanoshell, and (d) cone like nanoshell.

Figure 2

SCS as a function of wavelength for (a) spherical Ag nanoparticles for different radii, (b) spherical nanoshell composed of dielectric core with a RI of 1.46 and Ag shell for different core radii, embedded in water with RI of 1.33.

Figure 3

(a) SCS and (b) absorption versus wavelength for spherical Ag nanoparticles (solid line) and plexciton spherical nanoshells (dashed line) consisting of Ag core with a radius of 20 nm coated with a 5 nm of QE. The inset of (a) shows the electric field profiles at wavelength of (a) 395 nm, (b) 407 nm and (c) 414 nm.

Figure 4

SCS versus wavelength for plexciton spherical nanoshell with different shell thicknesses.

Figure 5

SCS versus wavelength for plexciton spherical nanoshell with different (a) number densities (b) dipole moments of QE.

Figure 6

(a) SCS and (b) absorption versus wavelength for elliptical Ag nanoparticles (solid line) and plexciton elliptical nanoshells (dashed line) consists of Ag core with a small radius of 10 nm and a large radius of 40 nm coated with a 5 nm of QE. The inset of (a) shows the electric field profiles at wavelength of (a) 783 nm, (b) 802 nm and (c) 823 nm.

Figure 7

(a) SCS versus wavelength for plexciton elliptical nanoshell with different RI of the environment. (b) The variation of maximum wavelengths versus RI of plexciton elliptical nanoshells.

Figure 8

SCS as a function of wavelength for plexciton elliptical nanoshells with different (a) small radii of core, (b) shell thicknesses.

Figure 9

SCS versus wavelength for plexciton elliptical nanoshell with different (a) number densities, (b) dipole moments of QE.

Figure 10

SCS versus wavelength for plexciton rod nanoshell consists of Ag core with a height of 80 nm and a radius of 10 nm coated with a 5 nm of QE with different (a) number densities, (b) dipole moments of QE.

Figure 11

(a) SCS versus wavelength for plexciton rod nanoshell with different RI of the environment. (b) The variation of maximum wavelengths versus RI of plexciton rod nanoshells.

Figure 12

SCS versus wavelength for plexciton cone like nanoshell consisting of Ag core with a height and a radius of 60 nm and 28 nm, respectively coated with a 5 nm of QE with different (a) number densities, (b) dipole moments of QE.

Figure 13

The ratio of two peaks in scattering curve versus RI for different nanoshell geometries.