| 1. |
- Bergstrand, Jan, et al.
(författare)
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On the decay time of upconversion luminescence
- 2019
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Ingår i: Nanoscale. - : Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 11:11, s. 4959-4969
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we systematically investigate the decay characteristics of upconversion luminescence (UCL) under anti-Stokes excitation through numerical simulations based on rate-equation models. We find that a UCL decay profile generally involves contributions from the sensitizer's excited-state lifetime, energy transfer and cross-relaxation processes. It should thus be regarded as the overall temporal response of the whole upconversion system to the excitation function rather than the intrinsic lifetime of the luminescence emitting state. Only under certain conditions, such as when the effective lifetime of the sensitizer's excited state is significantly shorter than that of the UCL emitting state and of the absence of cross-relaxation processes involving the emitting energy level, the UCL decay time approaches the intrinsic lifetime of the emitting state. Subsequently, Stokes excitation is generally preferred in order to accurately quantify the intrinsic lifetime of the emitting state. However, possible cross-relaxation between doped ions at high doping levels can complicate the decay characteristics of the luminescence and even make the Stokes-excitation approach fail. A strong cross-relaxation process can also account for the power dependence of the decay characteristics of UCL.
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| 2. |
- Huang, Kai, et al.
(författare)
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Protected excitation-energy reservoir for efficient upconversion luminescence
- 2017
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Ingår i: Nanoscale. - : Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 10:1, s. 250-259
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Tidskriftsartikel (refereegranskat)abstract
- Lanthanide-doped upconversion nanoparticles (UCNPs) are of great interest for biomedical applications. Currently, the applicability of UCNP bionanotechnology is hampered by the general low luminescence intensity of UCNPs and inefficient energy transfer from UCNPs to surface-bound chromophores used e.g. for photodynamic therapy or analyte sensing. In this work, we address the low efficiency issue by developing versatile core-shell nanostructures, where high-concentration sensitizers and activators are confined in the core- and shell region, representatively for hexagonal NaYF4:Yb, Er UCNPs. After doping concentration optimization, the sensitizer-rich core, is able to harvest/accumulate more excitation energy and generate almost one order of magnitude higher luminescence intensity than conventional homogeneously doped nanostructures. At the same time, the activator ions located in the shell enable a ~6 times more efficient resonant energy transfer from UCNPs to surface-bound acceptor dye molecules due to the short distance between donor-acceptor pairs. Our work provides new insights into the rational design of UCNPs and will greatly increase the general applicability of upconversion nanotechnologies.
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| 3. |
- Labrador-Páez, Lucia, et al.
(författare)
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Frequency-Domain Method for Characterization of Upconversion Luminescence Kinetics
- 2023
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 14:14, s. 3436-3444
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Tidskriftsartikel (refereegranskat)abstract
- The frequency-domain (FD) method provides an alternative to the commonly used time-domain (TD) approach in characterizing the luminescence kinetics of luminophores, with its own strengths, e.g., the capability to decouple multiple lifetime components with higher reliability and accuracy. While extensively explored for characterizing luminophores with down-shifted emission, this method has not been investigated for studying nonlinear luminescent materials such as lanthanide-doped upconversion nanoparticles (UCNPs), featuring more complicated kinetics. In this work, employing a simplified rate-equation model representing a standard two-photon energy-transfer upconversion process, we thoroughly analyzed the response of the luminescence of UCNPs in the FD method. We found that the FD method can potentially obtain from a single experiment the effective decay rates of three critical energy states of the sensitizer/activator ions involved in the upconversion process. The validity of the FD method is demonstrated by experimental data, agreeing reasonably well with the results obtained by TD methods.
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| 4. |
- Mousavi, Monirehalsadat, et al.
(författare)
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Beam-profile-compensated quantum yield measurements of upconverting nanoparticles
- 2017
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 19:33, s. 22016-22022
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Tidskriftsartikel (refereegranskat)abstract
- The quantum yield is a critically important parameter in the development of lanthanide-based upconverting nanoparticles (UCNPs) for use as novel contrast agents in biological imaging and optical reporters in assays. The present work focuses on the influence of the beam profile in measuring the quantum yield (φ) of nonscattering dispersions of nonlinear upconverting probes, by establishing a relation between φ and excitation light power density from a rate equation analysis. A resulting 60% correction in the measured φ due to the beam profile utilized for excitation underlines the significance of the beam profile in such measurements, and its impact when comparing results from different setups and groups across the world.
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| 5. |
- Rietsch, Philipp, et al.
(författare)
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Fluorescence of a chiral pentaphene derivative derived from the hexabenzocoronene Motif
- 2019
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1364-548X .- 1359-7345. ; 55:71, s. 10515-10518
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Tidskriftsartikel (refereegranskat)abstract
- A new fluorescent pentaphene derivative is presented that differs from hexabenzocoronene (HBC) by one carbon atom in the basal plane skeleton. A 500% increased fluorescence quantum yield is measured compared to the HBC derivative. The pentaphene compound, obtained by a modified Scholl oxidation, is also emissive in the solid-state, due to the packing motif in the crystal.
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