Improvement in the Luminescence Properties and Processability of LaF<sub>3</sub>/Ln and LaPO<sub>4</sub>/Ln Nanoparticles by Surface Modification

Stouwdam, Jan W.; Veggel, Frank C. J. M. van

doi:10.1021/la048379g

Cited by 241 publications

(223 citation statements)

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“…S7). [28] Because RE luminescence can be quenched by hydroxyl groups through multiphonon relaxation, [29] a reduction of the hydroxyl content, for example, by co-doping alkali metal ions, [30] could potentially increase the luminescence intensity of the RE-doped nanocrystalline titania microspheres. Photoluminescence emission spectra were also taken for the Eu-doped titania microspheres that were thermally treated at different temperatures.…”

mentioning

confidence: 99%

Rare‐Earth‐Doped Nanocrystalline Titania Microspheres Emitting Luminescence via Energy Transfer

et al. 2008

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Rare earth (RE) ions exhibit rich spectroscopic properties. Their 4f orbitals are buried beneath the 6s, 5p, and 5d orbitals, which weakens the coupling between the 4f orbitals and the surrounding ligands. The f-f transitions are parity-forbidden. As a result, RE luminescence emissions arising from 4f intrashell transitions are sharp, photostable, and long-lived. RE emission linewidths are typically 10-20 nm, [1] smaller than those of dye molecules (30-50 nm) and semiconductor nanocrystals (25-40 nm).[2] Moreover, RE emissions are much more photostable than those of dye molecules and semiconductor nanocrystals. Further, the luminescence lifetime of RE ions is ls-ms, while that of semiconductor nanocrystals is 10-40 ns and that of dye molecules is on the order of ns. RE ions can thus be used as probes for time-gated detection to efficiently suppress scattered light and short-lived auto-fluorescence from cells and tissues. Such attractive spectroscopic properties make RE ions potentially useful for a variety of fluorescence-based signaling and imaging techniques. RE ions also exhibit sharp absorption lines due to their 4f intrashell transitions. Their absorption cross sections are small because of parity forbidden f-f transitions. Although multiple RE ions can be simultaneously excited either by the use of a wide band light source whose emission band overlaps with the absorption bands of all RE ions [1] or through energy transfer between different RE ions, [3] the excitation is inefficient and often a laser source at a particular wavelength is required to excite one RE ion and then transfer the absorbed energy to other RE ions.[3] The capability to excite RE ions efficiently in a broad spectral range is strongly desired for realizing their full potential in signaling and imaging applications. We report here on RE-doped nanocrystalline titania microspheres that exhibit bright narrow bandwidth emission from RE ions when excited above the semiconductor bandgap of titania nanocrystals. Titania nanocrystals surrounded by regions of amorphous titania act as effective light-harvesting antennae to absorb light and transfer energy to RE ions, which emit intense sharp luminescence. We further demonstrate the generation of multiple photoluminescence emission lines with single-wavelength excitation by doping multiple RE ions into nanocrystalline titania microspheres. These microspheres can potentially be encapsulated with a thin shell of silica to depress the photocatalytic activity of titania and facilitate bioconjugation.[4] They therefore hold enormous potential in multiplexed signaling and bioassays, as have been demonstrated with polymer spheres embedded with semiconductor nanocrystals [5] and silica spheres doped with dye molecules.[6] Our nanocrystalline titania microspheres function as both a matrix for the uniform incorporation of RE ions and a sensitizer for RE luminescence, which is different from previously demonstrated energy transfer systems using clays [7] and zeolites. [8] In those experiments, clays and zeo...

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confidence: 99%

Rare‐Earth‐Doped Nanocrystalline Titania Microspheres Emitting Luminescence via Energy Transfer

et al. 2008

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“…More specifically, LaF 3 is chosen because in both bulk (11,12) and NP form (13)(14)(15) it is a well studied optical material that possesses low vibrational energies, high thermal and chemical stability, and high solid-solubility for optically active rare earth (co)dopants. The method of synthesis used here is an extension of the procedure developed by Dang et al (13) and modified by Stouwdam and van Veggel (14).…”

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confidence: 99%

“…To mitigate this issue, passive LaF 3 shells are grown around the lanthanide-doped core (re-ferred to within this text as ''simple core-shell'' NPs). NPs grown in this way have been shown to exhibit radiative quantum efficiency and lifetime values that approach those of the bulk LaF 3 (15,18). To make complex core-shell structures, we have extended Stouwdam and van Veggel's method for producing simple core-shell particles to produce multiple concentric shells.…”

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confidence: 99%

Controlling energy transfer between multiple dopants within a single nanoparticle

DiMaio

Sabatier²,

Kokuoz

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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Complex core-shell architectures are implemented within LaF3 nanoparticles to allow for a tailored degree of energy transfer (ET) between different rare earth dopants. By constraining specific dopants to individual shells, their relative distance to one another can be carefully controlled. Core-shell LaF 3 nanoparticles doped with Tb 3؉ and Eu 3؉ and consisting of up to four layers were synthesized with an outer diameter of Ϸ10 nm. It is found that by varying the thicknesses of an undoped layer between a Tb 3؉ -doped layer and a Eu 3؉ -doped layer, the degree of ET can be engineered to allow for zero, partial, or total ET from a donor ion to an acceptor ion. More specifically, the ratio of the intensities of the 541-nm Tb 3؉ and 590 nm Eu 3؉ peaks was tailored from <0.2 to Ϸ2.4 without changing the overall composition of the particles but only by changing the internal structure. Further, the emission spectrum of a blend of singly doped nanoparticles is shown to be equivalent to the spectra of co-doped particles when a core-shell configuration that restricts ET is used. Beyond simply controlling ET, which can be limiting when designing materials for optical applications, this approach can be used to obtain truly engineered spectral features from nanoparticles and composites made from them. Further, it allows for a single excitation source to yield multiple discrete emissions from numerous lanthanide dopants that heretofore would have been quenched in a more conventional active optical material.core-shell ͉ rare earth T he past 10 years have witnessed an increase in research on rare earth-doped nanoparticles (NP) because of the numerous applications to which they may be applied. The rare earth ions, typically trivalent, although sometimes di-or tetravalent, can exhibit luminescent emissions ranging from 172 nm to Ͼ7 m providing that they are doped into a host of high intrinsic transparency and low vibrational energy. Because of such a broad spectral range of potential emissions, active NPs are being considered for practical use in LEDs (1), solar cell energy conversion (2, 3), lasers and amplifiers (4), and biological assaying (5, 6).Heavy metal halide crystals are known to be excellent host materials for rare earth ions because of their intrinsically low phonon energies. Unfortunately, they also tend to be hygroscopic, brittle, and not thermally robust. One solution to this problem was found in the development of glass-ceramics, where halide nanocrystallites are nucleated in an oxide glass matrix. Some of the optically active rare earth (RE) ions partition into the crystallites and emit from lower vibrational energy host nanocrystals with improved quantum efficiencies than if they were emitting from the oxide host matrix (7). For example, LaF 3 nanocrystals were precipitated from oxyfluoride compositions by Dejneka (8) to create glasses that were more easily processed than fluoride glasses while maintaining their superior optical properties over oxide glasses (8). While this approach is beneficial for improving t...

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“…The post-synthetic modification of metal oxide nanoparticles has been investigated in a large number of cases, and with very different goals, not only for an enhancement of colloidal stability of the nanoparticles, but also to adjust many other properties, for example the optical and photocatalytic performance (Rehm et al, 1996;Rajh et al, 1999Rajh et al, , 2002Stowdam & van Veggel, 2004). Different classes of surface modifiers that have shown to be especially suitable for metal oxides include alkoxysilanes and chlorosilanes (Sanchez et al, 2001), carboxylic acids (Bourlinos et al, 2002;Arita et al, 2010), or phosphonic/phosphoric acid derivatives (Rill et al, 2007;Lomoschitz et al, 2011).…”

Section: Post-synthetic Stabilisationmentioning

confidence: 99%

In-Situ Versus Post-Synthetic Stabilization of Metal Oxide Nanoparticles

Garnweitner¹

2012

The Delivery of Nanoparticles

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Improvement in the Luminescence Properties and Processability of LaF₃/Ln and LaPO₄/Ln Nanoparticles by Surface Modification

Cited by 241 publications

References 16 publications

Rare‐Earth‐Doped Nanocrystalline Titania Microspheres Emitting Luminescence via Energy Transfer

Rare‐Earth‐Doped Nanocrystalline Titania Microspheres Emitting Luminescence via Energy Transfer

Controlling energy transfer between multiple dopants within a single nanoparticle

In-Situ Versus Post-Synthetic Stabilization of Metal Oxide Nanoparticles

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Improvement in the Luminescence Properties and Processability of LaF3/Ln and LaPO4/Ln Nanoparticles by Surface Modification

Cited by 241 publications

References 16 publications

Rare‐Earth‐Doped Nanocrystalline Titania Microspheres Emitting Luminescence via Energy Transfer

Rare‐Earth‐Doped Nanocrystalline Titania Microspheres Emitting Luminescence via Energy Transfer

Controlling energy transfer between multiple dopants within a single nanoparticle

In-Situ Versus Post-Synthetic Stabilization of Metal Oxide Nanoparticles

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Improvement in the Luminescence Properties and Processability of LaF₃/Ln and LaPO₄/Ln Nanoparticles by Surface Modification