Resonant Plasmon-Enhanced Upconversion in Monolayers of Core–Shell Nanocrystals: Role of Shell Thickness

Abstract

The upconversion luminescence (UCL) of colloidal lanthanide-doped upconversion nanocrystals (UCNCs) can be improved either by precise encapsulation of the surface by optically inert shells around the core, by an alteration of the nearby environment via metal nanoparticles, or by a combination of both. Considering their potential importance in crystalline silicon photovoltaics, the present study investigates both effects for two-dimensional arrangements of UCNCs. Using excitation light of 1500 nm wavelength, we study the variation in the upconversion luminescence from an Er 3+ -doped NaYF 4 core as a function of the thickness of a NaLuF 4 shell in colloidal solutions as well as in spin-cast-assisted self-assembled monolayers of UCNCs. The observed UCL yields and decay times of Er 3+ ions of the UCNCs increase with increasing shell thickness in both cases, and nearly no variation in decay times is observed in the transition of the UCNCs from solution to film configurations. The luminescence efficiency of the UCNC monolayers is further enhanced by electron-beam-lithographic-designed Au nanodiscs deposited either on top of or buried within the monolayer. It is observed that the improvement by the nanocrystal shells is greater than that of the Au nanodiscs.

Improving the efficiency of upconversion by light concentration using nanoparticle design

“…Nevertheless, the extinction computed by the S ext method can be shown -under simplifying circumstances, such as for isolated nanoparticles -to agree with (108) [124]. Indeed, we have on several occasions obtained very decent quantitative agreement with extinction measurements on randomly-distributed nanoparticles [23,125], which at least approximately behaves as isolated nanoparticles. An example is shown in figure 20(c).…”

Understanding the Shell Passivation in Ln3+‐Doped Luminescent Nanocrystals

“…Adapted with permission. [30] Copyright 2019, American Chemical Society. i) Shell thickness-dependent decay time of Yb 3þ 2 F 5/2 !…”

Design Strategy for Nanostructured Arrays of Metallodielectric Cuboids to Systematically Tune the Optical Response and Eliminate Spurious Bulk Effects in Plasmonic Biosensors

“…However, when monitoring adsorption or binding processes in situ, shifts in the plasmonic spectrum are not only caused by surface-bound molecules but also by changes in the bulk refractive index of the solutions, which may, e.g., occur upon solution exchange and deteriorate the results. Core-shell nanoparticle-based sensors [ 14 , 15 , 16 , 17 , 18 ] have been shown to overcome this problem for specific angles of light incidence. At a so-called “magic angle”, [ 19 ] molecule adsorption is still detected while the device is insensitive to bulk refractive index changes [ 20 , 21 ].…”