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14 pages, 3395 KiB

Open AccessArticle

NaYF₄ Microstructure, beyond Their Well-Shaped Morphology

by Godefroy Leménager, Sandrine Tusseau-Nenez, Maud Thiriet, Pierre-Eugène Coulon, Khalid Lahlil, Eric Larquet and Thierry Gacoin

Nanomaterials 2019, 9(11), 1560; https://doi.org/10.3390/nano9111560 - 04 Nov 2019

Cited by 8 | Viewed by 2922

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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15 pages, 5137 KiB

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

by Wen-Jeng Ho, Jheng-Jie Liu, Zong-Xian Lin and Hung-Pin Shiao

Nanomaterials 2019, 9(11), 1518; https://doi.org/10.3390/nano9111518 - 25 Oct 2019

Cited by 10 | Viewed by 3052

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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14 pages, 2247 KiB

Open AccessArticle

Towards Blue Long-Lasting Luminescence of Eu/Nd-Doped Calcium-Aluminate Nanostructured Platelets via the Molten Salt Route

by Rocío E. Rojas-Hernandez, Fernando Rubio-Marcos, Aida Serrano, Eduardo Salas, Irina Hussainova and José Francisco Fernandez

Nanomaterials 2019, 9(10), 1473; https://doi.org/10.3390/nano9101473 - 16 Oct 2019

Cited by 18 | Viewed by 2849

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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14 pages, 2786 KiB

Open AccessArticle

Explanation for the Multi-Component Scintillation of Cerium Fluoride Through the Equilibrium and Photophysical Investigation of Cerium(III)-Fluoro Complexes

by Zsolt Valicsek, Máté Kovács and Ottó Horváth

Nanomaterials 2019, 9(10), 1462; https://doi.org/10.3390/nano9101462 - 15 Oct 2019

Cited by 3 | Viewed by 2697

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 [Ce^IIIF_x(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 [Ce^IIIF_x(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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10 pages, 2077 KiB

Open AccessArticle

Optically Stimulated Nanodosimeters with High Storage Capacity

by David Van der Heggen, Daniel R. Cooper, Madeleine Tesson, Jonas J. Joos, Jan Seuntjens, John A. Capobianco and Philippe F. Smet

Nanomaterials 2019, 9(8), 1127; https://doi.org/10.3390/nano9081127 - 05 Aug 2019

Cited by 28 | Viewed by 6087

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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12 pages, 4247 KiB

Open AccessArticle

Eu³⁺, Tb³⁺- and Er³⁺, Yb³⁺-Doped α-MoO₃ Nanosheets for Optical Luminescent Thermometry

by Jing Liu, Rik Van Deun and Anna M. Kaczmarek

Nanomaterials 2019, 9(4), 646; https://doi.org/10.3390/nano9040646 - 21 Apr 2019

Cited by 15 | Viewed by 4155

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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29 pages, 20091 KiB

Open AccessArticle

Intrinsic Defect Engineering in Eu³ Doped ZnWO₄ for Annealing Temperature Tunable Photoluminescence⁺

by Bao-gai Zhai, Long Yang and Yuan Ming Huang

Nanomaterials 2019, 9(1), 99; https://doi.org/10.3390/nano9010099 - 15 Jan 2019

Cited by 19 | Viewed by 2824

Abstract

Eu³⁺ doped ZnWO₄ phosphors were synthesized via the co-precipitation technique followed by subsequent thermal annealing in the range of 400–1000

^{\circ}

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

^{\circ}

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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28 pages, 4601 KiB

Open AccessReview

Nanophosphors-Based White Light Sources

by Maura Cesaria and Baldassare Di Bartolo

Nanomaterials 2019, 9(7), 1048; https://doi.org/10.3390/nano9071048 - 22 Jul 2019

Cited by 16 | Viewed by 5645

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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21 pages, 6103 KiB

Open AccessReview

Luminescent Hydroxyapatite Doped with Rare Earth Elements for Biomedical Applications

by Ionela Andreea Neacsu, Alexandra Elena Stoica, Bogdan Stefan Vasile and Ecaterina Andronescu

Nanomaterials 2019, 9(2), 239; https://doi.org/10.3390/nano9020239 - 10 Feb 2019

Cited by 103 | Viewed by 7493

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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