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Title: Quantum Yields, Surface Quenching, and Passivation Efficiency for Ultrasmall Core/Shell Upconverting Nanoparticles

Abstract

We synthesized and characterized a set of ultrasmall hexagonal-phase NaGdF 4: 20% Yb 3+, 2% Er 3+ upconversion nanoparticles with core diameters of 3.7 ± 0.5 nm. In order to assess passivation effects and the influence of possible core-shell intermixing and to identify optimum particle structures for combined imaging in the visible and near-infrared (vis-NIR: 410-850 nm) and short-wave infrared (SWIR: 1520 nm), NaYF 4 shells of varying thicknesses (monolayer to 10 nm) were introduced and the influence of this parameter on the upconversion and downshifting photoluminescence of these particles was studied at different excitation power densities. This included excitation power-dependent emission spectra, slope factors, quantum yields, and excited state decay kinetics. These measurements demonstrated enhancement factors of the upconversion quantum yield of >10 000 in the low power region and an excitation power density-independent quantum yield of the downshifted emission at 1520 nm between 0.1 and 14%. The optimized shell thickness for combined vis and SWIR imaging was identified as 5 nm. Furthermore, lifetimes and quantum yields can be continuously tuned by shell thickness which can be exploited for lifetime multiplexing and encoding. The fact that we did not observe a saturation of the upconversion quantum yield or themore » excited state decay kinetics with increasing shell thickness is ascribed to a strong intermixing of the active core with the inert shell during the shelling procedure. This implies the potential of spectroscopic tools to detect cation intermixing.« less

Authors:
ORCiD logo [1]; ORCiD logo [2];  [1]; ORCiD logo [3]; ORCiD logo [1]
  1. Federal Institute for Materials Research and Testing (BAM), Berlin (Germany)
  2. Univ. of California, Berkeley, CA (United States)
  3. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC); German Research Foundation (DFG)
OSTI Identifier:
1545138
Grant/Contract Number:  
AC02-05CH11231
Resource Type:
Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 140; Journal Issue: 14; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Würth, Christian, Fischer, Stefan, Grauel, Bettina, Alivisatos, A. Paul, and Resch-Genger, Ute. Quantum Yields, Surface Quenching, and Passivation Efficiency for Ultrasmall Core/Shell Upconverting Nanoparticles. United States: N. p., 2018. Web. doi:10.1021/jacs.8b01458.
Würth, Christian, Fischer, Stefan, Grauel, Bettina, Alivisatos, A. Paul, & Resch-Genger, Ute. Quantum Yields, Surface Quenching, and Passivation Efficiency for Ultrasmall Core/Shell Upconverting Nanoparticles. United States. doi:10.1021/jacs.8b01458.
Würth, Christian, Fischer, Stefan, Grauel, Bettina, Alivisatos, A. Paul, and Resch-Genger, Ute. Fri . "Quantum Yields, Surface Quenching, and Passivation Efficiency for Ultrasmall Core/Shell Upconverting Nanoparticles". United States. doi:10.1021/jacs.8b01458. https://www.osti.gov/servlets/purl/1545138.
@article{osti_1545138,
title = {Quantum Yields, Surface Quenching, and Passivation Efficiency for Ultrasmall Core/Shell Upconverting Nanoparticles},
author = {Würth, Christian and Fischer, Stefan and Grauel, Bettina and Alivisatos, A. Paul and Resch-Genger, Ute},
abstractNote = {We synthesized and characterized a set of ultrasmall hexagonal-phase NaGdF4: 20% Yb3+, 2% Er3+ upconversion nanoparticles with core diameters of 3.7 ± 0.5 nm. In order to assess passivation effects and the influence of possible core-shell intermixing and to identify optimum particle structures for combined imaging in the visible and near-infrared (vis-NIR: 410-850 nm) and short-wave infrared (SWIR: 1520 nm), NaYF4 shells of varying thicknesses (monolayer to 10 nm) were introduced and the influence of this parameter on the upconversion and downshifting photoluminescence of these particles was studied at different excitation power densities. This included excitation power-dependent emission spectra, slope factors, quantum yields, and excited state decay kinetics. These measurements demonstrated enhancement factors of the upconversion quantum yield of >10 000 in the low power region and an excitation power density-independent quantum yield of the downshifted emission at 1520 nm between 0.1 and 14%. The optimized shell thickness for combined vis and SWIR imaging was identified as 5 nm. Furthermore, lifetimes and quantum yields can be continuously tuned by shell thickness which can be exploited for lifetime multiplexing and encoding. The fact that we did not observe a saturation of the upconversion quantum yield or the excited state decay kinetics with increasing shell thickness is ascribed to a strong intermixing of the active core with the inert shell during the shelling procedure. This implies the potential of spectroscopic tools to detect cation intermixing.},
doi = {10.1021/jacs.8b01458},
journal = {Journal of the American Chemical Society},
number = 14,
volume = 140,
place = {United States},
year = {2018},
month = {3}
}

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