Experimental demonstration of plasmon enhanced energy transfer rate in NaYF4:Yb3+,Er3+ upconversion nanoparticles

Abstract

Energy transfer upconversion (ETU) is known to be the most efficient frequency upconversion mechanism. Surface plasmon can further enhance the upconversion process, opening doors to many applications. However, ETU is a complex process involving competing transitions between multiple energy levels and it has been difficult to precisely determine the enhancement mechanisms. In this paper, we report a systematic study on the dynamics of the ETU process in NaYF4:Yb3+,Er3+ nanoparticles deposited on plasmonic nanograting structure. From the transient near-infrared photoluminescence under various excitation power densities, we observed faster energy transfer rates under stronger excitation conditions until it reached saturation where the highest internal upconversion efficiency was achieved. The experimental data were analyzed using the complete set of rate equations. The internal upconversion efficiency was found to be 56% and 36%, respectively, with and without the plasmonic nanograting. We also analyzed the transient green emission and found that it is determined by the infrared transition rate. To our knowledge, this is the first report of experimentally measured internal upconversion efficiency in plasmon enhanced upconversion material. Our work decouples the internal upconversion efficiency from the overall upconverted luminescence efficiency, allowing more targeted engineering for efficiency improvement.

Upconversion of low-energy photons in semiconductor nanostructures for solar energy harvesting

“…To improve coupling of incident, low-energy light with upconverters, Lu et al used a 1D silver nanograting to support surface plasmon resonance, improving iUQE [defined by Lu as the ratio of the energy transfer upconversion (ETU) rate to the NIR transition rate] in NaYF 4 :Yb 3+ ,Er 3+ from 36% to 56%. 87 Specifically, when the plasmon resonance is equal to the incident excitation frequency, the ETU rate (i.e., the product of the energy transfer coefficient and excited-state population) increases 2.7-fold, relative to low-energy radiative and nonradiative decay processes. Sensitization of lanthanides using organic, IR dyes such as IR-806 leads to further improved absorption across more visible spectral bands, 25,88 with 3300× increase in the integrated spectral response (in the absorption range 720-1100 nm), and 1100× increase in peak upconversion PL intensity (at 800 nm).…”

Over 1000-fold enhancement of upconversion luminescence using water-dispersible metal-insulator-metal nanostructures

“…For both samples, higher power densities result in shorter decay times. This is because at high power densities the intermediate energy levels are highly populated so the energy transfer upconversion rate is increased, resulting in a faster overall decay rate for the NIR emission 33 . In the strong excitation regime, we measure a decay rate of 3.00 × 10 4 s −1 for the MIM and 1.26 × 10 4 s −1 for the reference.…”

“…In the weak excitation regime, we measure a decay rate of 1.67 × 10 4 s −1 for the MIM and 5.71 × 10 3 s −1 for the reference. In the weak excitation regime, upconversion rate is small and only the intrinsic decay process affects the lifetime 33 . Thus, by comparing the NIR decay at weak excitation power densities, we extract a NIR quenching factor, Q NIR of 2.9.…”

“…In this paper, we report over 1000-fold enhancement of NaYF 4 :Yb 3+ ,Er 3+ UCNPs incorporated in a metal–insulator–metal (MIM) nanostructure. The MIMs are fabricated using laser interference lithography, a scalable technique which results in a large area and high uniformity 32 , 33 , 42 – 45 . We first optimize the geometry to achieve resonance at 980 nm and thus maximize enhancement in absorption.…”

Modulated Luminescence of Lanthanide Materials by Local Surface Plasmon Resonance Effect

“…Then, they further reported a systematic study on the increased energy transfer UC process of NaYF 4 : Yb 3+ , Er 3+ NPs on plasmonic nanograting structure. The internal UC efficiency was enhanced from 36% to 56% by the plasmonic nanograting [ 152 ]. Yang et al improved the UC luminescence of Nd 3+ -sensitized NaYF 4 : Yb 3+ , Er 3+ NPs by using tunable plasmonic Au films with ultra-broad plasmonic absorption.…”