Engineering upconversion emission spectra using plasmonic nanocavities

Abstract

We show that the upconversion emission spectra of Tm³⁺ and Yb³⁺ codoped β-NaYF₄-NaYF₄ core-shell nanoparticles can be judiciously modified by means of plasmonic nanocavities. Our analysis indicates that more than a 30-fold increase in conversion efficiency to the UV spectral band can be expected by engineering the NIR absorption and the local density of states. The effect of the nanocavity on the resulting radiation patterns is discussed. Our results are exemplified in cylindrical cavity geometries.

Enhanced UV upconversion emission using plasmonic nanocavities

“…These in turn influence the overall dynamics of the UC system. A rate equation model incorporating these aspects was previously reported by our group [28].…”

“…In this configuration, approximately ten β-NaYF 4 : Gd 3+ /Yb 3+ /Tm 3+ @NaLuF 4 core-shell nanoparticles with diameters on the order of 30 nm (core particles are only 17-18nm) are first embedded in PMMA and then encapsulated in a silver cavity. The increased upconversion is attributed to the presence of the metallic resonator that provides higher absorption at NIR, larger electromagnetic local density of states, and more efficient light outcoupling [28]. Furthermore, we systematically investigate the UV and visible upconversion enhancement in a number of nanoresonators as well as in several metal platforms including silver (Ag), aluminum (Al), and gold (Au).…”

Enhanced UV Upconversion Emission Using Plasmonic Nanocavities

“…In order to overcome the limitations imposed by the non-radiative decay rates, one can use an ensemble of upconverting nanoparticles in a more structured arrangement such as those encountered in nanocavities [28]. There are several advantages associated with this approach: (i) it reduces the non-radiative transitions and dissipative losses per UCNP, (ii) the resonator allows to engineer the spectral distribution of the photonic density of states, (iii) the cavity provides a more effective interface for transferring energy to the targets in the mesoscopic range.…”

“…2(b)). For simulation purposes, the net absorption coefficient of such UCNP enriched polymer is taken to be 5 cm −1 [28]. Figures 2(a) and (b) show the result of such simulations performed for a nanocavity with a cross-shape geometry surrounded by air and silver walls (50 nm), respectively.…”

“…Figure 2(c) shows the spectrum of the LDOS for a cross-shape silver cavity. Once the absorption enhancement and LDOS at various transitions are calculated, one can incorporate this data in the rate equation model to find the resulting modified spectra of the UCNPs trapped in plasmonic nanocavities [28].…”