Dual-resonance enhancement upconversion luminescence by elongated Ag semi-shell coated on NaYF4:Yb,Er@SiO2 nanorod

Plasmonic resonance induced by metallic structures is a feasible solution to enhance the upconversion luminescence (UCL) of lanthanide-doped nanocrystals. A simulation investigation on the optical properties of an elongated Ag semi-shell coated on nanorod is carried out in this paper. Nondegenerate longitudinal and radial void modes in the Ag cavity can be tuned almost independently and controllably to resonate with excitation and emission simultaneously via adjusting the length and diameter of the nanorod respectively. Moreover, both mode volumes are concentrated in the central region of the cavity. Spectral-plus spatial-overlapping ensures that the elongated Ag semi-shell is an efficient dual-resonance enhancement plasmonic structure. Under dual-resonance conditions, green UCL can achieve 718-fold enhancement when radial resonance overlapping with green UCL, while red UCL can achieve 141-fold enhancement when overlapping with red UCL, with original quantum efficiency (eta(0)) of 1%, both values are higher than that of gold nanorod. Since Purcell effect, resonating with different emission bands can realize color modulation, the intensity ratio of green UCL to red can raise to 9.1 or lower to 1.1 from the original 2.0. Although enhancement gradually weakens with the increase of eta(0), more than 20-fold enhancement can be still obtained even with eta(0) up to 33%.

Automated summary

This paper conducts a simulation study on the optical properties of an elongated Ag semi-shell coated on a nanorod. It is found that the nondegenerate longitudinal and radial void modes in the Ag cavity can be independently and controllably tuned to resonate with excitation and emission. The elongated Ag semi-shell acts as an efficient dual-resonance plasmonic structure, achieving significant enhancement of green and red upconversion luminescence.