Enhancing Up-Conversion Luminescence Using Dielectric Metasurfaces: Role of the Quality Factor of Resonance at a Pumping Wavelength

Abstract

Photonic applications of up-conversion luminescence (UCL) suffer from poor external quantum yield owing to a low absorption cross-section of UCL nanoparticles (UCNPs) doped with lanthanide ions. In this regard, plasmonic nanostructures have been proposed for enhancing UCL intensity through strong electromagnetic local-field enhancement; however, their intrinsic ohmic loss opens additional nonradiative decay channels. Herein, we demonstrate that dielectric metasurfaces can overcome this disadvantage. A periodic array of amorphous-silicon nanodisks serves as a metasurface on which a layer of UCNPs is self-assembled. Sharp resonances supported by the metasurface overlap the absorption wavelength (λ = 980 nm) of UCNPs to excite them, resulting in the enhancement of UCL intensity. We further sharpen the resonances through rapid thermal annealing (RTA) of the metasurface, crystallizing silicon to reduce intrinsic optical losses. By optimizing the RTA condition (at 1000 °C for 20 min in N2/H2 (3 vol %) atmosphere), the resonance quality factor improves from 17.2 to 32.9, accompanied by an increase in the enhancement factor of the UCL intensity from 86- to over 600-fold. Moreover, a reduction in the intrinsic optical losses mitigates the UCL thermal quenching under a high excitation density. These findings provide a strategy for increasing light–matter interactions in nanophotonic composite systems and promote UCNP applications.

Strategy of Charge Compensation for High-Performance Ni2+-Activated MgAl2O4 Spinel Near-Infrared Phosphor Synthesis via the Sol–Gel Combustion Method

“…To circumvent the issue of serious heat accumulation under high-power density, alaser diode (LD), which has advantages in compactness, brightness, and efficiency over LED chips, is gradually replacing LED as the alternative excitation light source. − We tested the feasibility of excitation using a high-power laser. The luminescence properties of Zr 4+ /Ni 2+ codoped MgAl 2 O 4 phosphors were excited with a monochromatic continuous wavelength (CW) laser with λ ex = 360 nm.…”