Direct Evidence of Significant Cation Intermixing in Upconverting Core@Shell Nanocrystals: Toward a New Crystallochemical Model

Hudry, Damien; Busko, Dmitry; Popescu, Radian; Gerthsen, D.; Abeykoon, A. M. Milinda; Kübel, Christian; Bergfeldt, Thomas; Richards, Bryce S.

doi:10.1021/acs.chemmater.7b03118

Cited by 72 publications

(88 citation statements)

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“…Typically, thicker shells increase UCQY values by reducing surface quenching effects, which can be minimized at shell thicknesses of 4–10 nm. 25,45–48 For a meaningful comparison between the samples, we factor out the effect of shell thickness by fitting the data to a simple model described by Equation 1. 47,49 The effect of surface quenching can be described by Förster-type energy transfer from a donor to a plane acceptor, the surface, by UCQY(d)=UCQY(d→∞)1+(d0/d)4.…”

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confidence: 99%

Small Alkaline-Earth-based Core/Shell Nanoparticles for Efficient Upconversion

et al. 2019

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The optical efficiency of lanthanide-based upconversion is intricately related to the crystalline host lattice. Different crystal fields interacting with the electron clouds of the lanthanides can significantly affect transition probabilities between the energy levels. Here, we investigate six distinct alkaline-earth rare-earth fluoride host materials (M1-xLnxF2+x, MLnF) for infrared-to-visible upconversion, focusing on nanoparticles of CaYF, CaLuF, SrYF, SrLuF, BaYF, and BaLuF doped with Yb3+ and Er3+. We first synthesize ~5 nm upconverting cores of each material via a thermal decomposition method. Then we introduce a dropwise hot-injection method to grow optically inert MYF shell layers around the active cores. Five distinct shell thicknesses are considered for each host material, resulting in 36 unique, monodisperse upconverting nanomaterials each with size below ~15nm. The upconversion quantum yield (UCQY) is measured for all core/shell nanoparticles as function of shell thickness and compared with hexagonal (β-phase) NaGdF4, a traditional upconverting host lattice. While the UCQY of core nanoparticles is below the detection limit (<10−5%), it increases by four to five orders of magnitude as the shell thickness approaches 4–6 nm. The UCQY values of our cubic MLnF nanoparticles meet or exceed the β-NaGdF4 reference sample. Across all core/shell samples, SrLuF nanoparticles are the most efficient, with UCQY values of 0.53% at 80 W/cm2 for cubic nanoparticles with ~11 nm edge length. This efficiency is 5 times higher than our β-NaGdF4 reference material with comparable core size and shell thickness. Our work demonstrates efficient and bright upconversion in ultra-small alkaline-earth-based nanoparticles, with applications spanning biological imaging and optical sensing.

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confidence: 99%

Small Alkaline-Earth-based Core/Shell Nanoparticles for Efficient Upconversion

et al. 2019

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“…The technique was first applied to characterize ultrasmall (≈10 nm) single‐shell upconverting NCs ( Figure , panel A) and recently extended to large (up to 50 nm) single‐ and multishell structures (Figure B–D) . These investigations shed new light on the formation of interfaces in core–shell upconverting NCs.…”

Section: Quantitative Chemical Analysis Of Core–shell Structuresmentioning

confidence: 99%

Section: Quantitative Chemical Analysis Of Core–shell Structuresmentioning

confidence: 99%

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Structure–Property Relationships in Lanthanide‐Doped Upconverting Nanocrystals: Recent Advances in Understanding Core–Shell Structures

et al. 2019

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The production of upconverting nanostructures with tailored optical properties is of major technological interest, and rapid progress toward the realization of such production has been made in recent years. Ultimately, accurate understanding of nanostructure organization will lead to design rules for accurately tailoring optical properties. Here, the context of open questions still of general importance to the upconversion and nanocrystal communities is presented, with a particular emphasis on the structure–property relationships of core–shell upconverting nanocrystals. Although the optical properties of the latter have been thoroughly investigated, little is known regarding their atomic‐scale organization. Indeed, solving the atomic‐scale structure of such nanomaterials is challenging because of their intrinsic nonperiodic nature. Familiar concepts of crystallography are no longer appropriate; chemical and structural modulation waves must be introduced. To reveal the exact core–shell structures, innovative characterization techniques need to be applied and developed, as discussed herein. The continued development and application of structural characterization techniques will be vital to consolidate the currently incomplete link between atomic‐scale structure and upconversion properties. This will ultimately provide a valuable contribution to the emerging detailed guidelines on how to better design upconverting nanostructures to achieve given optical properties in terms of efficiency, absorption, spectral emission, and dynamics.

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“…Recently, for the synthesis of lanthanide‐activated phosphors, ion exchange arises widespread attention, and provides an alternative solution in the modulation of energy transfer and luminescence enhancement . Nevertheless, for the Ce 3+ or Eu 2+ ‐doped phosphors contained Ca 2+ , Sr 2+ and Ba 2+ ions, there are few reports in this research area so far, and the search of suitable exchange media may be the key bottleneck need to be solved.…”

Section: Introductionmentioning

confidence: 99%

Facile Post‐Synthesis of a Ce³⁺‐Doped Ca_xSr_1‐xSc₂O₄ Phosphor by Means of Cation Exchange

Wang

Liu

et al. 2018

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Ion exchange is a useful method to synthesize the materials by the ion replacement from the template crystal structure. Here, by means of the cation exchange technique, we demonstrate a facile post‐synthesis CaxSr1‐xSc2O4:Ce3+ from SrSc2O4:Ce3+. In this exchange process, the framework of ScO6 octahedra is remaining, and Sr2+ ions are substituted by the Ca2+ ions from the CaCl2 melt. After optimizing the relevant parameters (the reaction mole ratio, temperature, and time), the largest exchange ratio could reach ∼97%. In addition, Ce3+ ions are almost not escaped through the exchange process, and the luminescent performance of final exchanged phosphors is comparable to the products from traditional bottom‐up approaches. Hence, the demonstration in this work manifests the excellent simplification and controllability of ion exchange in adjusting the luminescent property of phosphors and gives some significant inspirations for the design and preparation of lanthanide‐activated materials.

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Direct Evidence of Significant Cation Intermixing in Upconverting Core@Shell Nanocrystals: Toward a New Crystallochemical Model

Cited by 72 publications

References 44 publications

Small Alkaline-Earth-based Core/Shell Nanoparticles for Efficient Upconversion

Small Alkaline-Earth-based Core/Shell Nanoparticles for Efficient Upconversion

Structure–Property Relationships in Lanthanide‐Doped Upconverting Nanocrystals: Recent Advances in Understanding Core–Shell Structures

Facile Post‐Synthesis of a Ce³⁺‐Doped Ca_xSr_1‐xSc₂O₄ Phosphor by Means of Cation Exchange

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Direct Evidence of Significant Cation Intermixing in Upconverting Core@Shell Nanocrystals: Toward a New Crystallochemical Model

Cited by 72 publications

References 44 publications

Small Alkaline-Earth-based Core/Shell Nanoparticles for Efficient Upconversion

Small Alkaline-Earth-based Core/Shell Nanoparticles for Efficient Upconversion

Structure–Property Relationships in Lanthanide‐Doped Upconverting Nanocrystals: Recent Advances in Understanding Core–Shell Structures

Facile Post‐Synthesis of a Ce3+‐Doped CaxSr1‐xSc2O4 Phosphor by Means of Cation Exchange

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Facile Post‐Synthesis of a Ce³⁺‐Doped Ca_xSr_1‐xSc₂O₄ Phosphor by Means of Cation Exchange