Rare Earths-Doped Materials

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Inorganic Crystalline Materials".

Deadline for manuscript submissions: closed (15 May 2022) | Viewed by 26076

Special Issue Editors

Faculty of Chemistry and Pharmacy, Sofia University, Sofia, Bulgaria
Interests: inorganic chemistry; material science; chemistry of rare earths; photocatalysis; environmental problems
Special Issues, Collections and Topics in MDPI journals
Department of Inorganic Chemistry, Faculty of Chemistry and Pharmacy, University of Sofia “St. Kliment Ohridsky”, Sofia, Bulgaria
Interests: solid-state chemistry; material characterization; crystallography; heterogeneous catalysis and photocatalysis
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Here we are coming with a proposal to you to participate in the Special Issue “Rare Earths-Doped Materials”. Rare earths (RE)-doped materials are intensively studied in the latest decades taking into account that works on REs have been published by MDPI in some earlier special issues as well. As topics for the Special Issue in question can be considered (i) Development and application of different methods such as precipitation, solvothermal, mechanoactivation, atomic layer deposition, chemical vapor deposition, etc. to obtaining RE doped materials with interesting properties and applications in different fields; (ii) Application of different techniques used for characterization of such materials; (iii) RE-doped materials with specific structural and optical properties including doped crystals, bulk materials, polycrystalline materials, composites, thin films, etc. Research on the optical properties of the materials mentioned can be considered as the most investigated due to the broad fields for application they have, such as sensors, phosphors, semiconductors, medical applications, etc. by this illustrating the enhancement of properties obtained by RE doping.

We call for contribution to the Special Issue “Rare Earths-Doped Materials”, in an attempt to illustrate the different aspects of properties and applications of these materials as well as to present the current state of the research related to REs.

Prof. Dr. Maria Milanova
Prof. Dr. Martin Tsvetkov
Guest Editors

Keywords

  • rare earth elements
  • single crystals
  • bulk materials
  • nano crystals
  • phosphors
  • composite materials
  • semiconductors
  • insulators

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Published Papers (9 papers)

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Editorial

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2 pages, 146 KiB  
Editorial
Rare Earths Doped Materials
Crystals 2021, 11(3), 231; https://doi.org/10.3390/cryst11030231 - 26 Feb 2021
Cited by 3 | Viewed by 1648
Abstract
Тhe properties of the Rare Earth Elements allow a wide range of applications in optoelectronics, fiber amplifiers, solid-state lasers, telecommunications, biosensing, and photocatalysis, just to mention a few [...] Full article
(This article belongs to the Special Issue Rare Earths-Doped Materials)

Research

Jump to: Editorial

20 pages, 4342 KiB  
Article
Features of the Phase Preferences, Long- and Short-Range Order in Ln2(WO4)3 (Ln = Gd, Dy, Ho, Yb) with Their Relation to Hydration Behavior
Crystals 2022, 12(7), 892; https://doi.org/10.3390/cryst12070892 - 23 Jun 2022
Viewed by 1217
Abstract
The effect of synthesis conditions on the features of the long- and short-range order of Ln2(WO4)3 (Ln = Gd, Dy, Ho, Yb) powders synthesized via coprecipitation of salts has been studied by a complex of physico-chemical techniques [...] Read more.
The effect of synthesis conditions on the features of the long- and short-range order of Ln2(WO4)3 (Ln = Gd, Dy, Ho, Yb) powders synthesized via coprecipitation of salts has been studied by a complex of physico-chemical techniques including synchrotron X-ray powder diffraction, X-ray absorption spectroscopy, Raman and infrared spectroscopy, and simultaneous thermal analysis. It was found that crystallization of amorphous precursors begins at 600 °C/3 h and leads to the formation of the monoclinic structure with sp. gr. C12/c1(15) for Ln2(WO4)3 (Ln = Gd, Dy) and with sp. gr. P121/a1(14) for Ln = Yb, whereas crystallization of Ho precursor requires even higher temperature. After annealing at 1000 °C, the P121/a1(14) phase becomes the dominant phase component for all heavy lanthanoid types except for Ln = Gd. It was shown that the Ln (Ln = Dy, Ho, and Yb) tungstates with the P121/a1(14) monoclinic structure correspond to trihydrates Ln2(WO4)3·3H2O formed due to a rapid spontaneous hydration under ambient conditions. It was concluded that the proneness to hydration is due to a specific structure of the P121/a1(14) phase with large voids available to water molecules. Modifications in the local structure of Ln-O coordination shell accompanying the structure type change and hydration are monitored using EXAFS spectroscopy. Full article
(This article belongs to the Special Issue Rare Earths-Doped Materials)
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15 pages, 9696 KiB  
Article
Characterization of Tungstates of the Type Hf1−xLnxW2O8−x/2 (Ln = Eu, Tm, Lu) Synthesized Using the Hydrothermal Method
Crystals 2022, 12(3), 327; https://doi.org/10.3390/cryst12030327 - 26 Feb 2022
Viewed by 1716
Abstract
Pure HfW2O8- and Ln3+-containing solid solutions, Hf1−xLnxW2O8−x/2 (Ln = Eu, Tm, Lu), were synthesized using the hydrothermal method. The lanthanide ions were selected based on the differences between their ionic [...] Read more.
Pure HfW2O8- and Ln3+-containing solid solutions, Hf1−xLnxW2O8−x/2 (Ln = Eu, Tm, Lu), were synthesized using the hydrothermal method. The lanthanide ions were selected based on the differences between their ionic radii. A content of the Ln3+ ions in the range of 0.01–0.15 mol with a step of 0.02 was used for Hf1−xLnxW2O8−x/2 preparation, although the main research was performed on x = 0.01 and 0.05 samples because of an inhomogeneity detected by powder X-ray diffraction (XRD) when the content of Ln3+ was above 0.07–0.09 mol. X-ray diffraction measurements were supported by Raman and infrared spectroscopy. A new band in the Raman spectra of the samples with 0.05 mol Ln3+, as well as a red shift of the most intensive band (assigned to valence stretching of W-O-W bonds) as a result of the Ln3+ presence, was detected. The Scanning Electron Microscopy and Transmission Electron Microscopy micrographs revealed well-crystalized microcrystals with lengths in the range of 2–5 μm, with larger interplanar distances, measured in the solid solutions of the same crystal plain. The alpha-HfW2O8 → beta-HfW2O8 order-to-disorder phase transition was followed by high temperature XRD, and its reversibility was evident. The influence of the Ln3+ both on the unit cell parameters of the solid solutions and on the temperature of phase transition and on the coefficient of thermal expansion, CTE, was observed. A band gap energy in the range of 2.8–3.1 eV for pure HfW2O8 and for the solid solutions Hf1−xLnxW2O8−x/2 (x = 0.01 and 0.05) was determined. Full article
(This article belongs to the Special Issue Rare Earths-Doped Materials)
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12 pages, 21287 KiB  
Article
Luminescence Properties of Gd2(MoO4)3 Modified with Sm(III) and Tb(III) for Potential LED Applications
Crystals 2022, 12(1), 120; https://doi.org/10.3390/cryst12010120 - 17 Jan 2022
Cited by 5 | Viewed by 1451
Abstract
Light-emitting phosphors, doped with lanthanide ions of Tb(III) and Sm(III) of the type Gd1.97−y SmyTb0.03(MoO4)3 (y = 0.01–0.11, step 0.02) and Gd1.95−xSm0.05Tbx(MoO4)3 (x = 0.01–0.09, step [...] Read more.
Light-emitting phosphors, doped with lanthanide ions of Tb(III) and Sm(III) of the type Gd1.97−y SmyTb0.03(MoO4)3 (y = 0.01–0.11, step 0.02) and Gd1.95−xSm0.05Tbx(MoO4)3 (x = 0.01–0.09, step 0.02), were synthesized and characterized by X-ray diffraction, UV-Vis spectroscopy, scanning and transmitting electron microscopy (SEM, TEM) as well as photoluminescence spectroscopy. The effect of the doping content of Tb/Sm was followed. The unit cell parameters for Gd1.97−ySmyTb0.03(MoO4)3 and Gd1.95−xSm0.05Tbx(MoO4)3 changed with the increase in the Tb/Sm content. The microstrain values also increased, proposing an increased concentration of defects. The mean particle size was estimated to be approximately 0.6 µm. Based on a Williamson–Hall plot, the size of the crystallites was determined to be in the range of 42–60 nm for modified and pure Gd2(MoO4)3 samples, respectively. The samples excited at 406 nm exhibited characteristic emission lines of Sm (485, 555, 646 nm). The host material Gd2(MoO4)3 emission in visible light was explained by the crystal structure defects, namely, oxygen vacancies. The CIE x/y color coordinates of the phosphors were determined and the related points were located in the green-yellow/pale yellow region of the visible light. The excited state lifetimes were determined for both groups of the samples, showing values in the millisecond range and indicating the samples as promising phosphors. Full article
(This article belongs to the Special Issue Rare Earths-Doped Materials)
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23 pages, 8308 KiB  
Article
Synthesis and Crystal Structure of the Short LnSb2O4Br Series (Ln = Eu–Tb) and Luminescence Properties of Eu3+-Doped Samples
Crystals 2020, 10(12), 1089; https://doi.org/10.3390/cryst10121089 - 27 Nov 2020
Cited by 10 | Viewed by 2838
Abstract
Pale yellow crystals of LnSb2O4Br (Ln = Eu–Tb) were synthesized via high temperature solid-state reactions from antimony sesquioxide, the respective lanthanoid sesquioxides and tribromides. Single-crystal X-ray diffraction studies revealed a layered structure in the monoclinic space group [...] Read more.
Pale yellow crystals of LnSb2O4Br (Ln = Eu–Tb) were synthesized via high temperature solid-state reactions from antimony sesquioxide, the respective lanthanoid sesquioxides and tribromides. Single-crystal X-ray diffraction studies revealed a layered structure in the monoclinic space group P21/c. In contrast to hitherto reported quaternary lanthanoid(III) halide oxoantimonates(III), in LnSb2O4Br the lanthanoid(III) cations are exclusively coordinated by oxygen atoms in the form of square hemiprisms. These [LnO8]13− polyhedra form layers parallel to (100) by sharing common edges. All antimony(III) cations are coordinated by three oxygen atoms forming ψ1-tetrahedral [SbO3]3− units, which have oxygen atoms in common building up meandering strands along [001] according to {[SbO2/2vO1/1t]}1 (v = vertex-sharing, t = terminal). The bromide anions are located between two layers of these parallel running oxoantimonate(III) strands and have no bonding contacts with the Ln3+ cations. Since Sb3+ is known to be an efficient sensitizer for Ln3+ emission, photoluminescence studies were carried out to characterize the optical properties and assess their suitability as light phosphors. Indeed, for both, GdSb2O4Br and TbSb2O4Br doped with about 1.0–1.5 at-% Eu3+ efficient sensitization of the Eu3+ emission could be detected. For TbSb2O4Br, in addition, a remarkably high energy transfer from Tb3+ to Eu3+ could be detected that leads to a substantially increased Eu3+ emission intensity, rendering it an efficient red light emitting material. Full article
(This article belongs to the Special Issue Rare Earths-Doped Materials)
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19 pages, 4377 KiB  
Article
Influence of Stabilizing Ion Content on the Structure, Photoluminescence and Biological Properties of Zr1–xEuxO2–0.5x Nanoparticles
Crystals 2020, 10(11), 1038; https://doi.org/10.3390/cryst10111038 - 15 Nov 2020
Cited by 5 | Viewed by 2517
Abstract
Quasi-spherical nanoparticles of ZrO2 containing EuO1.5 from 2 to 15 mol.% were synthesized from the chlorides of the corresponding metals under hydrothermal conditions. The structural changes of Zr1–xEuxO2–0.5x (x = 0.02 ÷ 0.15) nanoparticles depending on [...] Read more.
Quasi-spherical nanoparticles of ZrO2 containing EuO1.5 from 2 to 15 mol.% were synthesized from the chlorides of the corresponding metals under hydrothermal conditions. The structural changes of Zr1–xEuxO2–0.5x (x = 0.02 ÷ 0.15) nanoparticles depending on the content of europium (III) ions were studied using the complementary methods (X-ray diffraction, electron microdiffraction, Raman and photoluminescence spectroscopy). It was shown that increasing the Eu3+ concentration in the Zr1–xEuxO2–0.5x nanoparticles leads to a transition from the equilibrium monoclinic zirconia phase to metastable tetragonal and cubic polymorphic modifications. In this case, the size of the nanoparticles decreases from 11.5 nm to 9 nm; the specific surface area grows from 80.2 to 111.3 m2/g, and the electrokinetic potential increases monotonously from −8.7 to 16.3 mV. The evolution of the phase composition of Zr1–xEuxO2-0.5x nanoparticles from monoclinic to tetragonal/cubic allomorphs with an increase in the molar fraction of stabilizer ions was correlated with changes in the sublevel structure of 5D07F2 and 5D07F4 optical transitions for Eu3+ in the luminescence spectra. Besides, for the nanoparticles obtained by hydrothermal synthesis from chlorides, the quantum efficiency does not exceed 3%. According to the M.T.T. assay, as a result of three-day human fibroblast cultivation in the aqueous dispersion of Zr1–xEuxO2–0.5x (x = 0.02 ÷ 0.15) nanoparticles, the proliferation activity of the cells is maintained, indicating that they do not have cytotoxic properties. Such nanoparticles can be used in organic–inorganic composites for medical applications in order to strengthen the polymer scaffolds and visualize changes in their structure within time. Full article
(This article belongs to the Special Issue Rare Earths-Doped Materials)
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16 pages, 5532 KiB  
Article
Symmetry of the Optical Phonons in LuVO4: A Raman Study
Crystals 2020, 10(5), 341; https://doi.org/10.3390/cryst10050341 - 26 Apr 2020
Cited by 4 | Viewed by 2802
Abstract
A thorough analysis of the first-order vibrational spectrum of LuVO4 is presented by using polarized micro-Raman spectroscopy with special focus on the phonon modes with the weakest intensity and occasional controversial assignment. Group-theory analysis is carried out to demonstrate the determination of [...] Read more.
A thorough analysis of the first-order vibrational spectrum of LuVO4 is presented by using polarized micro-Raman spectroscopy with special focus on the phonon modes with the weakest intensity and occasional controversial assignment. Group-theory analysis is carried out to demonstrate the determination of numbers and symmetries of the Raman active modes. Crystal- and correlation-field splitting effects in the vibrational spectrum of LuVO4 are discussed. Under conditions adjusted to minimize the birefringence effects we recorded, in each main scattering configuration, a series of Raman spectra in different sample orientations achieved by rotating the sample around the incident laser beam. The dependence of the Raman intensity on the rotational angle allowed us to identify the correct symmetry of the phonons with exceptionally weak scattering cross-section. A complete assignment of all twelve first-order Raman active phonons of LuVO4 is thus obtained. Full article
(This article belongs to the Special Issue Rare Earths-Doped Materials)
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14 pages, 3796 KiB  
Article
Optical Investigation of Eu3+ Doped Bi12GeO20 (BGO) Crystals
Crystals 2020, 10(4), 285; https://doi.org/10.3390/cryst10040285 - 09 Apr 2020
Cited by 13 | Viewed by 7462
Abstract
The spectroscopic properties of Eu3+ doped Bi12GeO20 (BGO) sillenite bulk crystals that were grown by the low-thermal-gradient Czochralski technique (LTG Cz) were investigated. The absorption spectra and the emission properties have been measured at room temperature (300 K) and [...] Read more.
The spectroscopic properties of Eu3+ doped Bi12GeO20 (BGO) sillenite bulk crystals that were grown by the low-thermal-gradient Czochralski technique (LTG Cz) were investigated. The absorption spectra and the emission properties have been measured at room temperature (300 K) and at 10 K. Luminescence was observed both due to the direct Eu3+ ion excitation, as well as under UV excitation due to the energy transfer between Bi3+ and Eu3+ ions. Bi3+ → Eu3+ energy transfer mechanisms in Eu3+:BGO doped host were investigated. The Ωλ parameters, as well as radiative lifetimes, were calculated based upon the Judd-Ofelt formalism. The branching ratios and electric dipole transition probabilities were also determined, based upon the obtained experimental results. Luminescence has been observed from the 5D0,1,2 levels of Eu3+, with emissions from the 5D0 level being the strongest. The strongest observed luminescence band corresponds to the 5D07F0 transition at 578.7 nm. Reasons for the strong presence of the theoretically forbidden 5D07F0 emission were investigated. Full article
(This article belongs to the Special Issue Rare Earths-Doped Materials)
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12 pages, 17272 KiB  
Article
Effect of the Fluorine Substitution for –OH Group on the Luminescence Property of Eu3+ Doped Hydroxyapatite
Crystals 2020, 10(3), 191; https://doi.org/10.3390/cryst10030191 - 10 Mar 2020
Cited by 12 | Viewed by 2926
Abstract
In this study, different fluoridated hydroxyapatite doped with Eu3+ ion nanoparticles were prepared by the hydrothermal method. The relationship between luminescence enhancement of Eu3+ ions and a fluorine substitution ratio for hydroxyl group in hydroxyapatite was discussed. Moreover, the effect of [...] Read more.
In this study, different fluoridated hydroxyapatite doped with Eu3+ ion nanoparticles were prepared by the hydrothermal method. The relationship between luminescence enhancement of Eu3+ ions and a fluorine substitution ratio for hydroxyl group in hydroxyapatite was discussed. Moreover, the effect of fluorine substitution for a hydroxyl group on phase composition, crystallinity, and crystal size was studied. Phase composition and chemical structures were identified by X-ray diffraction (XRD) and Fourier Transform Infrared (FT-IR) Spectroscopy analyses. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) patterns were performed to analyze the morphology and particle size. X-ray Photoelectron Spectroscopy (XPS) patterns were observed to analyze fluorine substitution for the hydroxyl group and chemical state of Eu3+ ions in fluoridated hydroxyapatite. The results of these experiments indicated that the samples with a different fluorine substitution ratio were prepared successfully by maintaining the apatite structure. With an increasing fluorine substitution ratio, the morphology maintained a rod-like structure but the aspect ratio tended to decrease. XPS patterns displayed that the fluorine replaced the hydroxyl group and brought environmental variation. The fluorine ions could affect the crystal field environment and promote luminescence conversion. There was a linear relationship between the fluorine substitution ratio and luminescence enhancement. Full article
(This article belongs to the Special Issue Rare Earths-Doped Materials)
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