Up-Conversion Luminescence Properties of Lanthanide-Gold Hybrid Nanoparticles as Analyzed with Discrete Dipole Approximation

Abstract

Up-conversion nanoparticles (UCNP) under near-infrared (NIR) light irradiation have been well investigated in the field of bio-imaging. However, the low up-conversion luminescence (UCL) intensity limits applications. Plasmatic modulation has been proposed as an effective tool to adjust the luminescence intensity and lifetime. In this study discrete dipole approximation (DDA) was explored concerning guiding the design of UCNP@mSiO2-Au structures with enhanced UCL intensity. The extinction effects of gold shells could be changed by adjusting the distance between the UCNPs and the Au NPs by synthesized tunable mesoporous silica (mSiO2) spacers. Enhanced UCL was obtained under 808 nm irradiation. Theoretical predictions could not be demonstrated to full extend by experimental data, indicating that better models for simulation need to better take into account inhomogeneities in particle morphologies.

Numerical Modelling of the Optical Properties of Plasmonic and Latex Nanoparticles to Improve the Detection Limit of Immuno-Turbidimetric Assays

“…The extinction cross-sections ( C ext ) of NPs with different composition, size, and arrangement in aqueous solution were evaluated with the Discrete Dipole Approximation (DDA) method [ 34 , 35 ]. In DDA, the structure of interest, called “target”, is modelled with a number N of polarizable points (dipoles) arranged in a cubic lattice with the same geometry and permittivity of the original object [ 34 , 36 , 37 , 38 ]. The basis of the DDA is that the polarization P j induced on each dipole j of position r j and polarizability p j is given by [ 34 , 36 , 37 , 38 ].…”

“…In DDA, the structure of interest, called “target”, is modelled with a number N of polarizable points (dipoles) arranged in a cubic lattice with the same geometry and permittivity of the original object [ 34 , 36 , 37 , 38 ]. The basis of the DDA is that the polarization P j induced on each dipole j of position r j and polarizability p j is given by [ 34 , 36 , 37 , 38 ]. where E Loc is the electric field originated by the incident radiation of amplitude E 0 , and includes the contribution of all other dipoles [ 34 , 36 , 37 , 38 ]: where is the interaction matrix and is the incident monochromatic plane wave with frequency ω and wavevector .…”

“…The extinction cross-section of the target is then given by [ 34 , 36 , 37 , 38 ] where is the complex conjugate of the incident electric field.…”

“…In this work, calculations were performed with the DDSCAT software [ 39 ], where p j is expressed according to the lattice dispersion relation (LDR) developed by Draine and Goodman [ 34 , 39 ], i.e., as a correction of the Clausius–Mossotti polarizability by a series expansion of k . d and ε m , with d the interdipole spacing and ε m the matrix dielectric constant [ 34 , 36 , 37 , 38 ]: where ε j is the dipole permittivity, b 1 , b 2 , b 3 , and S are coefficients of the expansions and is the Clausius–Mossotti polarizability [ 34 , 36 , 37 , 38 ] …”