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- 저자 : Tajon, Cheryl A. (검색결과 2 건)
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Enrichment of molecular antenna triplets amplifies upconverting nanoparticle emission
Garfield, David J.,Borys, Nicholas J.,Hamed, Samia M.,Torquato, Nicole A.,Tajon, Cheryl A.,Tian, Bining,Shevitski, Brian,Barnard, Edward S.,Suh, Yung Doug,Aloni, Shaul,Neaton, Jeffrey B.,Chan, Emory M Nature Publishing Group UK 2018 Nature photonics Vol.12 No.7
<P>Efficient photon upconversion at low light intensities promises major advances in technologies spanning solar energy harvesting to deep-tissue biophotonics. Here, we discover the critical mechanisms that enable near-infrared dye antennas to significantly enhance performance in lanthanide-doped upconverting nanoparticle (UCNP) systems, and leverage these findings to design dye-UCNP hybrids with a 33,000-fold increase in brightness and a 100-fold increase in efficiency over bare UCNPs. We show that increasing the lanthanide content in the UCNPs shifts the primary energy donor from the dye singlet to its triplet, and the resultant triplet states then mediate energy transfer into the nanocrystals. Time-gated phosphorescence, density functional theory, singlet lifetimes and triplet-quenching experiments support these findings. This interplay between the excited-state populations in organic antennas and the composition of UCNPs presents new design rules that overcome the limitations of previous upconverting materials, enabling performances now relevant for photovoltaics, biophotonics and infrared detection.</P>
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Continuous-wave upconverting nanoparticle microlasers
Fernandez-Bravo, Angel,Yao, Kaiyuan,Barnard, Edward S.,Borys, Nicholas J.,Levy, Elizabeth S.,Tian, Bining,Tajon, Cheryl A.,Moretti, Luca,Altoe, M. Virginia,Aloni, Shaul,Beketayev, Kenes,Scotognella, F Nature Publishing Group UK 2018 Nature nanotechnology Vol.13 No.7
Reducing the size of lasers to microscale dimensions enables new technologies<SUP>1</SUP> that are specifically tailored for operation in confined spaces ranging from ultra-high-speed microprocessors<SUP>2</SUP> to live brain tissue<SUP>3</SUP>. However, reduced cavity sizes increase optical losses and require greater input powers to reach lasing thresholds. Multiphoton-pumped lasers<SUP>4–7</SUP> that have been miniaturized using nanomaterials such as lanthanide-doped upconverting nanoparticles (UCNPs)<SUP>8</SUP> as lasing media require high pump intensities to achieve ultraviolet and visible emission and therefore operate under pulsed excitation schemes. Here, we make use of the recently described energy-looping excitation mechanism in Tm<SUP>3+</SUP>-doped UCNPs<SUP>9</SUP> to achieve continuous-wave upconverted lasing action in stand-alone microcavities at excitation fluences as low as 14 kW cm<SUP>−2</SUP>. Continuous-wave lasing is uninterrupted, maximizing signal and enabling modulation of optical interactions<SUP>10</SUP>. By coupling energy-looping nanoparticles to whispering-gallery modes of polystyrene microspheres, we induce stable lasing for more than 5 h at blue and near-infrared wavelengths simultaneously. These microcavities are excited in the biologically transmissive second near-infrared (NIR-II) window and are small enough to be embedded in organisms, tissues or devices. The ability to produce continuous-wave lasing in microcavities immersed in blood serum highlights practical applications of these microscale lasers for sensing and illumination in complex biological environments.
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