Single-nanocrystal sensitivity achieved by enhanced upconversion luminescence

Abstract

Upconversion nanocrystals convert infrared radiation to visible luminescence, and are promising for applications in biodetection, bioimaging, solar cells and three-dimensional display technologies. Although the design of suitable nanocrystals has improved the performance of upconversion nanocrystals, their emission brightness is limited by the low doping concentration of activator ions needed to avoid the luminescence quenching that occurs at high concentrations. Here, we demonstrate that high excitation irradiance can alleviate concentration quenching in upconversion luminescence when combined with higher activator concentration, which can be increased from 0.5 mol% to 8 mol% Tm(3+) in NaYF₄. This leads to significantly enhanced luminescence signals, by up to a factor of 70. By using such bright nanocrystals, we demonstrate remote tracking of a single nanocrystal with a microstructured optical-fibre dip sensor. This represents a sensitivity improvement of three orders of magnitude over benchmark nanocrystals such as quantum dots.

Multi-photon quantum cutting in Gd2O2S:Tm3+ to enhance the photo-response of solar cells

“…This means that the cross-relaxation rate of the 1 G 4 level in a nearest-neighbor pair is 1/0.16 ms, 6603 faster than radiative decay. Such fast cross-relaxation rates explain why in upconversion experiments only low Tm 31 concentrations of no higher than 1% yield bright blue upconversion emission [44][45][46] .…”

Tailored Near‐Infrared Photoemission in Fluoride Perovskites through Activator Aggregation and Super‐Exchange between Divalent Manganese Ions

“…It has hence been crucial to design (nano) materials that exhibit both emission and excitation of luminescence in the NIR region for in vitro and in vivo imaging applications 24, 25. For example, rare‐earth‐doped nanocrystals have attracted considerable interest in recent years as potential candidates for high‐resolution bioimaging because such nanocrystals may exhibit NIR upconversion (UC) emission upon excitation by a 976 nm laser diode (LD) 26, 27, 28, 29. However, the accompanying intrinsically strong VIS emission that is additionally occurring in these rare‐earth‐doped materials limits the emission penetration depth in biological tissue because of the tissue's low transparency for wavelengths below 600 nm 30…”

High-Precision Pinpointing of Luminescent Targets in Encoder-Assisted Scanning Microscopy Allowing High-Speed Quantitative Analysis

“…After removing the supernatant containing unbound biotinylated DNA, the functionalized UCNPs were redispersed into 100 µl deionised water. The concentration was 2 mg/ml (corresponding to 15.6 nM) 35 assuming no loss in the preparation steps above.…”

“…Improved sensitivity by orders of magnitude has been demonstrated compared to the conventional fluorescence methods, taking advantage of either time-gated detection or near-infrared (NIR) excitation to remove the autofluorescence background [34][35][36] . We have also shown recently that luminescence lifetimes of lanthanide-based upconversion materials can be fine-tuned across the microsecond to millisecond range, allowing for creation of temporally multiplexed codes for luminescence detaction 33,37 .…”