title: 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.
authors.affiliation: Advanced Cytometry Laboratories, MQ Photonics Research Centre and MQ BioFocus Research Centre, Macquarie University, Sydney, New South Wales 2109, Australia.
authors.forename: Jiangbo
authors.initials: J
authors.lastname: Zhao
authors.forename: Dayong
authors.initials: D
authors.lastname: Jin
authors.forename: Erik P
authors.initials: EP
authors.lastname: Schartner
authors.forename: Yiqing
authors.initials: Y
authors.lastname: Lu
authors.forename: Yujia
authors.initials: Y
authors.lastname: Liu
authors.forename: Andrei V
authors.initials: AV
authors.lastname: Zvyagin
authors.forename: Lixin
authors.initials: L
authors.lastname: Zhang
authors.forename: Judith M
authors.initials: JM
authors.lastname: Dawes
authors.forename: Peng
authors.initials: P
authors.lastname: Xi
authors.forename: James A
authors.initials: JA
authors.lastname: Piper
authors.forename: Ewa M
authors.initials: EM
authors.lastname: Goldys
authors.forename: Tanya M
authors.initials: TM
authors.lastname: Monro
mesh_terms: D015374:Biosensing Techniques; D049449:Luminescence; D046529:Microscopy, Electron, Transmission; D053758:Nanoparticles / Q000737:chemistry*; D036103:Nanotechnology / Q000379:methods*; D010316:Particle Size; D015019:Yttrium / Q000737:chemistry
chemical_list: D015019:Yttrium