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Zhou B.,Institute of Materials Research and Engineering of Singapore | Shi B.,Macquarie University | Jin D.,Macquarie University | Jin D.,University of Technology, Sydney | And 3 more authors.
Nature Nanotechnology | Year: 2015

Lanthanide-doped upconversion nanocrystals enable anti-Stokes emission with pump intensities several orders of magnitude lower than required by conventional nonlinear optical techniques. Their exceptional properties, namely large anti-Stokes shifts, sharp emission spectra and long excited-state lifetimes, have led to a diversity of applications. Here, we review upconversion nanocrystals from the perspective of fundamental concepts and examine the technical challenges in relation to emission colour tuning and luminescence enhancement. In particular, we highlight the advances in functionalization strategies that enable the broad utility of upconversion nanocrystals for multimodal imaging, cancer therapy, volumetric displays and photonics. © 2015 Macmillan Publishers Limited. All rights reserved.

Wang F.,Institute of Materials Research and Engineering of Singapore | Wang F.,City University of Hong Kong | Deng R.,City University of Hong Kong | Liu X.,Institute of Materials Research and Engineering of Singapore | And 2 more authors.
Nature Protocols | Year: 2014

Sodium gadolinium fluoride (NaGdF4) is an ideal host material for the incorporation of luminescent lanthanide ions because of its high photochemical stability, low vibrational energy and its ability to mediate energy exchanges between the lanthanide dopants. This protocol describes the detailed experimental procedure for synthesizing core-shell NaGdF4 nanoparticles that incorporate lanthanide ions into different layers for efficiently converting a single-wavelength, near-IR excitation into a tunable visible emission. These nanoparticles can then be used as luminescent probes in biological samples, in 3D displays, in solar energy conversion and in photodynamic therapy. The NaGdF4 nanoparticles are grown through co-precipitation in a binary solvent mixture of oleic acid and 1-octadecene. Doping by lanthanides with controlled compositions and concentrations can be achieved concomitantly with particle growth. The lanthanide-doped NaGdF4 nanoparticles then serve as seed crystals for subsequent epitaxial growth of shell layers comprising different lanthanide dopants. The entire procedure for the preparation and isolation of the core-shell nanoparticles comprising two epitaxial shell layers requires ∼15 h for completion. © 2014 Nature America, Inc. All rights reserved.

Yang W.,Institute of Materials Research and Engineering of Singapore | Li X.,National University of Singapore | Chi D.,Institute of Materials Research and Engineering of Singapore | Zhang H.,CAS Changchun Institute of Applied Chemistry | And 3 more authors.
Nanotechnology | Year: 2014

Photovoltaics and photocatalysis are two significant applications of clean and sustainable solar energy, albeit constrained by their inability to harvest the infrared spectrum of solar radiation. Lanthanide-doped materials are particularly promising in this regard, with tunable absorption in the infrared region and the ability to convert the long-wavelength excitation into shorter-wavelength light output through an upconversion process. In this review, we highlight the emerging applications of lanthanide-doped upconversion materials in the areas of photovoltaics and photocatalysis. We attempt to elucidate the fundamental physical principles that govern the energy conversion by the upconversion materials. In addition, we intend to draw attention to recent technologies in upconversion nanomaterials integrated with photovoltaic and photocatalytic devices. This review also provides a useful guide to materials synthesis and optoelectronic device fabrication based on lanthanide-doped upconversion materials. © 2014 IOP Publishing Ltd.

Zhou B.,Institute of Materials Research and Engineering of Singapore | Yang W.,Institute of Materials Research and Engineering of Singapore | Han S.,National University of Singapore | Sun Q.,National University of Singapore | And 2 more authors.
Advanced Materials | Year: 2015

A strategy of interfacial energy transfer upconversion is demonstrated through the use of a terbium (Tb3+) dopant as energy donor or energy migrator in core-shell-structured nanocrystals. This mechanistic investigation presents a new pathway for photon upconversion, and, more importantly, contributes to the better control of energy transfer at the nanometer length scale. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Peng J.,Agency for Science, Technology and Research Singapore | Xu W.,National University of Singapore | Teoh C.L.,Agency for Science, Technology and Research Singapore | Han S.,National University of Singapore | And 10 more authors.
Journal of the American Chemical Society | Year: 2015

Development of highly sensitive and selective sensing systems of divalent zinc ion (Zn2+) in organisms has been a growing interest in the past decades owing to its pivotal role in cellular metabolism, apoptosis, and neurotransmission. Herein, we report the rational design and synthesis of a Zn2+ fluorescent-based probe by assembling lanthanide-doped upconversion nanoparticles (UCNPs) with chromophores. Specifically, upconversion luminescence (UCL) can be effectively quenched by the chromophores on the surface of nanoparticles via a fluorescence resonant energy transfer (FRET) process and subsequently recovered upon the addition of Zn2+, thus allowing for quantitative monitoring of Zn2+. Importantly, the sensing system enables detection of Zn2+ in real biological samples. We demonstrate that this chromophore-UCNP nanosystem is capable of implementing an efficient in vitro and in vivo detection of Zn2+ in mouse brain slice with Alzheimers disease and zebrafish, respectively. © 2015 American Chemical Society.

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