Special Issue "Luminescent Rare-Earth Based Nanomaterials"

A special issue of Nanomaterials (ISSN 2079-4991).

Deadline for manuscript submissions: closed (30 September 2019).

Special Issue Editor

Dr. Anna M. Kaczmarek
Website
Guest Editor
Universiteit Gent, Department of Chemistry, Ghent, Belgium
Interests: lanthanide luminescence; temperature-dependent luminescence; ratiometric temperature sensors; cryogenic sensing; anti-counterfeiting; up-conversion; nanomaterials; core-shell structures; polyoxometalates; metal organic frameworks; periodic mesoporous organosilica

Special Issue Information

Dear Colleagues,

Rare-earth-based materials are attracting a wide range of interest due to their optical properties, which have found a wide spectrum of applications such as solid-state lighting, lasers, solar cells, biological imaging, biosensors, and optoelectronics to name a few. Preparing these materials at the nano-size is crucial for many current and future applications.

Rare-earth-based nanomaterials exhibit important advantages over other available luminescent nanomaterials due to their low toxicity, photostability, high thermal and chemical stability, sharp emission bands, high luminescence quantum yields and relatively long luminescence decay times. Among the most common inorganic matrices are the fluoride matrix (very low vibrational energies) as well as the tungstate, molybdate and vanadate matrices. An important research topic concerning rare-earth-based nanomaterials is the development of core–shell nanoparticles and up-conversion nanoparticles. Up-conversion is the process where the absorption of two or more photons leads to the emission of light at shorter wavelengths than the excitation wavelength, which means that near-infrared excitation is converted to visible wavelengths. Developing core–shell nanostructures allows minimizing the surface quenching effects, which results in the enhanced luminescence of such materials. Recently a very attractive topic has been nanothermometers and rare-earth-based nanothermometers. They are crucial for the development of temperature sensors in nanoelectronics, nanophotonics, chemical microreactors and thermal barrier coatings.

The Special Issue on “Luminescent rare-earth-based nanomaterials” will cover a wide range of research fields, including rare-earths and nanomaterials, nanofabrication, core–shell structures, nanosensors, bioprobes, and security devices in the form of reviews, communications, and academic articles.

Potential topics include, but are not limited to:

  1. Development of core–shell up-conversion nanoparticles
  2. Energy transfer in core-shell type nanoparticles
  3. Novel ratiometric temperature nanosensors
  4. Near-infrared emitting systems
  5. Development of bioprobes based on rare-earth-doped nanoparticles
  6. Rare-earth nanomaterials for anti-counterfeit applications
  7. Applications of rare-earth-based nanomaterials

Dr. Anna M. Kaczmarek
Guest Editor

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • nanomaterials
  • nanophosphors
  • nanomaterials synthesize and characterization
  • rare-earths
  • lanthanides
  • luminescence
  • optical properties
  • up-conversion
  • down-conversion
  • core–shell
  • bioprobes
  • temperature nanosensors
  • energy transfer

Published Papers (9 papers)

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Research

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Open AccessArticle
NaYF4 Microstructure, beyond Their Well-Shaped Morphology
Nanomaterials 2019, 9(11), 1560; https://doi.org/10.3390/nano9111560 - 04 Nov 2019
Abstract
Lanthanide-doped nanoparticles are widely investigated for their optical properties. However, the sensitivity of the lanthanide ions’ luminescence to the local symmetry, useful when investigating structural environments, becomes a drawback for optimized properties in the case of poorly controlled crystallinity. In this paper, we [...] Read more.
Lanthanide-doped nanoparticles are widely investigated for their optical properties. However, the sensitivity of the lanthanide ions’ luminescence to the local symmetry, useful when investigating structural environments, becomes a drawback for optimized properties in the case of poorly controlled crystallinity. In this paper, we focus on β -NaYF4 nanorods in order to provide a detailed description of their chemical composition and microstructure. The combination of detailed XRD analysis and TEM observations show that strong variation may be observed from particles from a same batch of synthesis, but also when considering small variations of synthesis conditions. Moreover, also the nanorods observed by SEM exhibit a very nice faceted shape, they are far from being monocrystalline and present significant local deviation of crystalline symmetry and orientation. All these structural considerations, sensitively probed by polarized emission analysis, are crucial to analyze for the development of optimal systems toward the targeted applications. Full article
(This article belongs to the Special Issue Luminescent Rare-Earth Based Nanomaterials)
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Open AccessArticle
Enhancing Photovoltaic Performance of GaAs Single-Junction Solar Cells by Applying a Spectral Conversion Layer Containing Eu-Doped and Yb/Er-Doped Phosphors
Nanomaterials 2019, 9(11), 1518; https://doi.org/10.3390/nano9111518 - 25 Oct 2019
Cited by 1
Abstract
In this study, we examined efforts to increase the photovoltaic performance of GaAs single-junction solar cells using spectral conversion layers, respectively, composed of europium-doped (Eu-doped) phosphors, ytterbium/erbium-doped (Yb/Er-doped) phosphors, and a combination of Eu-doped and Yb/Er-doped phosphors. Spin-on film deposition was used to [...] Read more.
In this study, we examined efforts to increase the photovoltaic performance of GaAs single-junction solar cells using spectral conversion layers, respectively, composed of europium-doped (Eu-doped) phosphors, ytterbium/erbium-doped (Yb/Er-doped) phosphors, and a combination of Eu-doped and Yb/Er-doped phosphors. Spin-on film deposition was used to apply the conversion layers, all of which had a total phosphor concentration of 3 wt%. The chemical compositions of the phosphors were examined by energy-dispersive X-ray spectroscopy. The fluorescence emissions of the phosphors were confirmed by using photoluminescence measurements. Under laser diode excitation at 405 nm, we observed green luminescent downshift (LDS) emissions by Eu-doped phosphors at wavelengths of 479 nm to 557 nm, and under excitation at 980 nm, we observed red up-conversion (UC) emissions by Yb/Er-doped phosphors at wavelengths of 647 nm to 672 nm. The spectral conversion layers were characterized in terms of optical reflectance, external quantum efficiency, and photovoltaic current and voltage under AM 1.5 G simulations. The conversion efficiency of the cell combining Eu-doped and Yb/Er-doped phosphors (23.84%) exceeded that of the cell coated with Yb/Er-doped phosphors (23.72%), the cell coated with Eu-doped phosphors (23.19%), and the cell coated without phosphors (22.91%). Full article
(This article belongs to the Special Issue Luminescent Rare-Earth Based Nanomaterials)
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Open AccessArticle
Towards Blue Long-Lasting Luminescence of Eu/Nd-Doped Calcium-Aluminate Nanostructured Platelets via the Molten Salt Route
Nanomaterials 2019, 9(10), 1473; https://doi.org/10.3390/nano9101473 - 16 Oct 2019
Cited by 2
Abstract
Calcia-alumina binary compounds doped with rare earths and some transition metals cations show persistent luminescence from the visible to the infrared range. Specifically, the blue light can be obtained through the Eu2+ activator center in a potential host, such as dodecacalcium hepta-aluminate [...] Read more.
Calcia-alumina binary compounds doped with rare earths and some transition metals cations show persistent luminescence from the visible to the infrared range. Specifically, the blue light can be obtained through the Eu2+ activator center in a potential host, such as dodecacalcium hepta-aluminate (Ca12Al14O33) and monocalcium aluminate (CaAl2O4). By doping with Nd3+, the persistent luminescence can be substantially prolonged; for this reason, the Eu/Nd pair is a potential choice for developing long-lasting blue luminescence. Herein, the phase evolution of the calcia-alumina system via molten salt synthesis is reported as a function of the synthesis temperature and the atmospheric environment. The fraction of CaAl2O4 phase increases when the temperature is higher. Synthesized microparticles of platelet-type morphology represent isolated nanostructured ceramic pieces. Under visible light, the particles are white. This indicates that the followed process solves the dark-gray coloring of phosphor when is synthesized in a reduced atmosphere at high temperature. As regards the synthesis mechanism, which is assisted by the molten flux, the dissolution−diffusion transport process is promoted at the surface of the alumina microparticles. In fact, the emission intensity can be modulated through the phase of the Eu-doped calcium-aluminate discrete platelets synthesized. Consequently, the photoluminescence intensity depends also on the oxidation state of the Eu ion. X-ray absorption near-edge structure and photoluminescence measurements corroborate the Eu reduction and the grain coarsening with the enhancement of the blue emission. The doped phosphors with Eu/Nd show a broad and strong absorption in the region of 320–400 nm and a broad emission band at around 440 nm when they are excited in this absorption range. From a broader perspective, our findings prove that the Ca12Al14O33 and CaAl2O4 phases open new opportunities for research into the design of blue long-lasting emitters for a wide range of fields from ceramic to optoelectronic materials. Full article
(This article belongs to the Special Issue Luminescent Rare-Earth Based Nanomaterials)
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Open AccessArticle
Explanation for the Multi-Component Scintillation of Cerium Fluoride Through the Equilibrium and Photophysical Investigation of Cerium(III)-Fluoro Complexes
Nanomaterials 2019, 9(10), 1462; https://doi.org/10.3390/nano9101462 - 15 Oct 2019
Abstract
CeF3 displays favorable scintillation properties, which have been utilized for decades in various solid-state systems. Its emission undergoes multi-component decays, which were interpreted by lattice defects and so-called intrinsic features herein. This study of the complex equilibria in connection with photophysical behavior [...] Read more.
CeF3 displays favorable scintillation properties, which have been utilized for decades in various solid-state systems. Its emission undergoes multi-component decays, which were interpreted by lattice defects and so-called intrinsic features herein. This study of the complex equilibria in connection with photophysical behavior of the cerium(III)-fluoride system in solution gave us the possibility to reveal the individual contribution of the [CeIIIFx(H2O)9−x]3−x species to the photoluminescence. Spectrophotometry and spectrofluorometry (also in time-resolved mode) were used, and combined with sophisticated evaluation methods regarding both the complex equilibria and the kinetics of the photoinduced processes. The individual photophysical parameters of the [CeIIIFx(H2O)9−x]3−x complexes were determined. For the kinetic evaluation, three methods of various simplifications were applied and compared. The results indicated that the rates of some excited-state equilibrium processes were comparable to those of the emission decay steps. Our results also contribute to the explanation of the multi-component emission decays in the CeF3-containing scintillators, due to the various coordination environments of Ce3+, which can be affected by the excitation leading to the dissociation of the metal-ligand bonds. Full article
(This article belongs to the Special Issue Luminescent Rare-Earth Based Nanomaterials)
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Open AccessArticle
Optically Stimulated Nanodosimeters with High Storage Capacity
Nanomaterials 2019, 9(8), 1127; https://doi.org/10.3390/nano9081127 - 05 Aug 2019
Abstract
In this work we report on the thermoluminescence (TL) and optically stimulated luminescence (OSL) properties of β-Na(Gd,Lu)F4:Tb3+ nanophosphors prepared via a standard high-temperature coprecipitation route. Irradiating this phosphor with X-rays not only produces radioluminescence but also leads to a bright [...] Read more.
In this work we report on the thermoluminescence (TL) and optically stimulated luminescence (OSL) properties of β-Na(Gd,Lu)F4:Tb3+ nanophosphors prepared via a standard high-temperature coprecipitation route. Irradiating this phosphor with X-rays not only produces radioluminescence but also leads to a bright green afterglow that is detectable up to hours after excitation has stopped. The storage capacity of the phosphor was found to be (2.83 ± 0.05) × 1016 photons/gram, which is extraordinarily high for nano-sized particles and comparable to the benchmark bulk phosphor SrAl2O4:Eu2+,Dy3+. By combining TL with OSL, we show that the relatively shallow traps, which dominate the TL glow curves and are responsible for the bright afterglow, can also be emptied optically using 808 or 980 nm infrared light while the deeper traps can only be emptied thermally. This OSL at therapeutically relevant radiation doses is of high interest to the medical dosimetry community, and is demonstrated here in uniform, solution-processable nanocrystals. Full article
(This article belongs to the Special Issue Luminescent Rare-Earth Based Nanomaterials)
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Open AccessArticle
Eu3+, Tb3+- and Er3+, Yb3+-Doped α-MoO3 Nanosheets for Optical Luminescent Thermometry
Nanomaterials 2019, 9(4), 646; https://doi.org/10.3390/nano9040646 - 21 Apr 2019
Cited by 4
Abstract
Here we report a novel synthesis approach for the preparation of α-MoO3:Ln3+ materials employing a two-step synthesis. Additionally, in this work the α-MoO3:Ln3+ materials are reported as potential optical thermometers for the first time. In this synthesis [...] Read more.
Here we report a novel synthesis approach for the preparation of α-MoO3:Ln3+ materials employing a two-step synthesis. Additionally, in this work the α-MoO3:Ln3+ materials are reported as potential optical thermometers for the first time. In this synthesis approach, first MoS2 2D nanosheets were prepared, which were further heat treated to obtain α-MoO3. These materials were fully characterized by powder X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray fluorescence (XRF), thermogravimetry (TG) and differential thermal analysis (DTA), transmission electron microscopy (TEM), and luminescence spectroscopy. Temperature-dependent luminescence measurements were carried out to determine the optical thermometric properties of two different types of α-MoO3:Ln3+ materials (Eu3+/Tb3+ downshifting and Er3+/Yb3+ upconversion luminescence systems). We demonstrate in this study that this class of material could be a potential candidate for temperature-sensing applications. Full article
(This article belongs to the Special Issue Luminescent Rare-Earth Based Nanomaterials)
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Open AccessArticle
Intrinsic Defect Engineering in Eu3 Doped ZnWO4 for Annealing Temperature Tunable Photoluminescence+
Nanomaterials 2019, 9(1), 99; https://doi.org/10.3390/nano9010099 - 15 Jan 2019
Cited by 4
Abstract
Eu3+ doped ZnWO4 phosphors were synthesized via the co-precipitation technique followed by subsequent thermal annealing in the range of 400–1000 C. The phase, morphology, elemental composition, chemical states, optical absorption, and photoluminescence (PL) of the phosphors were characterized by X-ray [...] Read more.
Eu3+ doped ZnWO4 phosphors were synthesized via the co-precipitation technique followed by subsequent thermal annealing in the range of 400–1000 C. The phase, morphology, elemental composition, chemical states, optical absorption, and photoluminescence (PL) of the phosphors were characterized by X-ray diffraction, scanning electron microscopy, dispersive X-ray spectroscopy, X-ray photoelectron spectrometry, diffuse UV–vis reflectance spectroscopy, PL spectrophotometry, and PL lifetime spectroscopy, respectively. It is found that the PL from Eu3+ doped ZnWO4 is tunable through the control of the annealing temperature. Density functional calculations and optical absorption confirm that thermal annealing created intrinsic defects in ZnWO4 lattices play a pivotal role in the color tunable emissions of the Eu3+ doped ZnWO4 phosphors. These data have demonstrated that intrinsic defect engineering in ZnWO4 lattice is an alternative and effective strategy for tuning the emission color of Eu3+ doped ZnWO4. This work shows how to harness the intrinsic defects in ZnWO4 for the preparation of color tunable light-emitting phosphors. Full article
(This article belongs to the Special Issue Luminescent Rare-Earth Based Nanomaterials)
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Review

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Open AccessReview
Nanophosphors-Based White Light Sources
Nanomaterials 2019, 9(7), 1048; https://doi.org/10.3390/nano9071048 - 22 Jul 2019
Cited by 1
Abstract
Miniaturization requests and progress in nanofabrication are prompting worldwide interest in nanophosphors as white-emission mercury-free lighting sources. By comparison with their bulk counterparts, nanophosphors exhibit reduced concentration quenching effects and a great potential to enhance luminescence efficiency and tunability. In this paper, the [...] Read more.
Miniaturization requests and progress in nanofabrication are prompting worldwide interest in nanophosphors as white-emission mercury-free lighting sources. By comparison with their bulk counterparts, nanophosphors exhibit reduced concentration quenching effects and a great potential to enhance luminescence efficiency and tunability. In this paper, the physics of the nanophoshors is overviewed with a focus on the impact of spatial confinement and surface-to-volume ratio on the luminescence issue, as well as rare earth-activated multicolor emission for white light (WL) output. In this respect, the prominently practiced strategies to achieve WL emission are single nanophosphors directly yielding WL by means of co-doping and superposition of the individual red, green, and blue emissions from different nanophosphors. Recently, a new class of efficient broadband WL emitting nanophosphors has been proposed, i.e., nominally un-doped rare earth free oxide (yttrium oxide, Y2O3) nanopowders and Cr transition metal-doped garnet nanocrystals. In regard to this unconventional WL emission, the main points are: it is strictly a nanoscale phenomenon, the presence of an emitting center may favor WL emission without being necessary for observing it, and, its inherent origin is still unknown. A comparison between such an unconventional WL emission and the existing literature is presented to point out its novelty and superior lighting performances. Full article
(This article belongs to the Special Issue Luminescent Rare-Earth Based Nanomaterials)
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Open AccessReview
Luminescent Hydroxyapatite Doped with Rare Earth Elements for Biomedical Applications
Nanomaterials 2019, 9(2), 239; https://doi.org/10.3390/nano9020239 - 10 Feb 2019
Cited by 9
Abstract
One new, promising approach in the medical field is represented by hydroxyapatite doped with luminescent materials for biomedical luminescence imaging. The use of hydroxyapatite-based luminescent materials is an interesting area of research because of the attractive characteristics of such materials, which include biodegradability, [...] Read more.
One new, promising approach in the medical field is represented by hydroxyapatite doped with luminescent materials for biomedical luminescence imaging. The use of hydroxyapatite-based luminescent materials is an interesting area of research because of the attractive characteristics of such materials, which include biodegradability, bioactivity, biocompatibility, osteoconductivity, non-toxicity, and their non-inflammatory nature, as well their accessibility for surface adaptation. It is well known that hydroxyapatite, the predominant inorganic component of bones, serves a substantial role in tissue engineering, drug and gene delivery, and many other biomedical areas. Hydroxyapatite, to the detriment of other host matrices, has attracted substantial attention for its ability to bind to luminescent materials with high efficiency. Its capacity to integrate a large assortment of substitutions for Ca2+, PO43−, and/or OH ions is attributed to the versatility of its apatite structure. This paper summarizes the most recently developed fluorescent materials based on hydroxyapatite, which use rare earth elements (REEs) as dopants, such as terbium (Tb3+), erbium (Er3+), europium (Eu3+), lanthanum (La3+), or dysprosium (Dy3+), that have been developed in the biomedical field. Full article
(This article belongs to the Special Issue Luminescent Rare-Earth Based Nanomaterials)
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