Rare Earth Phosphates Research Articles

Rare earth metals detection and recognition based on laser induced breakdown spectroscopy and machine learning.

The rapid detection and identification of the electronic waste (e-waste) containing rare earth (RE) elements is of great significance for the recycling of RE elements. However, the analysis of these materials is extremely challenging due to extreme similarities in appearance or chemical composition. In this research, a new system based on laser induced breakdown spectroscopy (LIBS) and machine learning algorithms is developed for identifying and classifying e-waste of rare-earth phosphors (REPs). Three different kinds of phosphors are selected and the spectra is monitored using this new developed system. The analysis of phosphor spectra shows that there are Gd, Yd, and Y RE element spectra in the phosphor. The results also verify that LIBS could be used to detect RE elements. An unsupervised learning method, principal component analysis (PCA), is used to distinguish the three phosphors and training data set is stored for further identification. Additionally, a supervised learning method, backpropagation artificial neural network (BP-ANN) algorithm is used to establish a neural network model to identify phosphors. The result show that the final phosphor recognition rate reaches 99.9%. The innovative system based on LIBS and machine learning (ML) has the potential to improve rapid in situ detection of RE elements for the classification of e-waste.

Temperature-dependent vacuum ultraviolet photoluminescence spectroscopy of transition metal and rare earth co-doped ZnO phosphors: a synchrotron-based investigation

Temperature-dependent vacuum ultraviolet photoluminescence spectroscopy of transition metal and rare earth co-doped ZnO phosphors: a synchrotron-based investigation

Stable white light emission from a single organic molecule via intermolecular hydrogen bond to excited-state intermolecular proton transfer

It is widely recognized that hybrid (organic/inorganic) light emitting diodes (LEDs) are of concern because they use an organic material instead of rare earth phosphors, but extending their lifetime remains challenging. To construct organic luminescent material with high photoluminescence quantum yield (PLQY), a compound named 1-(4-(tert-butyl)phenyl)-2-(4′-(1-phenyl-1H-benzo[d]imidazol-2-yl)-[1,1′-biphenyl]-4-yl)-1H-phenanthro[9,10-d]imidazole (TPBI-BPI) was synthesized by connect two imidazoles units. The PLQY of TPBI-BPI is 0.97 in acetonitrile. The white light emission (WLE) of TPBI-BPI in ethyl acetate solution containing acetic acid was observed, and a solvent-type organic/inorganic hybrid white LED device based on TPBI-BPI was prepared. The luminance efficiency, external quantum efficiency, correlated color temperature, K, and Ra (color rendering index) of the solvent-type WLED are 21.71 lm/W, 12.76%, 6329, and 83.2 at 39.90 mA, respectively. The Commission Internationale de l´Eclairage coordinate of the solvent-type WLED is (0.3135, 0.3507). In addition, the lifetime (T70) of the device can reach 130 h. This is due to the excited state intermolecular proton transfer between TPBI-BPI and acetic acid in ethyl acetate solution after UV illumination. This enables TPBI-BPI to obtain WLE and makes the WLED spectrally stable due to this process's dissipation of UV energy. This work provides a strategy to extend the lifetime of a hybrid LED.

Xenotime-type high-entropy (Dy1/7Ho1/7Er1/7Tm1/7Yb1/7Lu1/7Y1/7)PO4: A promising thermal/environmental barrier coating material for SiCf/SiC ceramic matrix composites

Rare-earth phosphates (REPO₄) are regarded as one of the promising thermal/environmental barrier coating (T/EBC) materials for SiC_f/SiC ceramic matrix composites (SiC-CMCs) owing to their excellent resistance to water vapor and CaO–MgO–Al₂O₃–SiO₂ (CMAS). Nevertheless, a relatively high thermal conductivity (<i>κ</i>) of the REPO₄ becomes the bottleneck for their practical applications. In this work, novel xenotime-type high-entropy (Dy_1/7Ho_1/7Er_1/7Tm_1/7Yb_1/7Lu_1/7Y_1/7)PO₄ (HE (7RE_1/7)PO₄) has been designed and synthesized for the first time to solve this issue. HE (7RE_1/7)PO₄ with a homogeneous rare-earth element distribution exhibits high thermal stability up to 1750 ℃ and good chemical compatibility with SiO₂ up to 1400 ℃. In addition, the thermal expansion coefficient (TEC) of HE (7RE_1/7)PO₄ (5.96×10⁻⁶ ℃⁻¹ from room temperature (RT) to 900 ℃) is close to that of the SiC-CMCs. What is more, the thermal conductivities of HE (7RE_1/7)PO₄ (from 4.38 W·m⁻¹·K⁻¹ at 100&nbsp;℃ to 2.25 W·m⁻¹·K⁻¹ at 1300 ℃) are significantly decreased compared to those of single-component REPO₄ with the minimum value ranging from 9.90 to 4.76 W·m⁻¹·K⁻¹. These results suggest that HE (7RE_1/7)PO₄ has the potential to be applied as the T/EBC materials for the SiC-CMCs in the future.

High-accuracy dual-mode optical thermometry based on up-conversion luminescence in Er3+/Ho3+-Yb3+ doped LaNbO4 phosphors

Due to the non-contact and high sensitivity, optical thermometry based on rare earth doped phosphors has been paid much attention to. Herein, dual-mode optical thermometers are designed using up-conversion luminescence of Er3+/Ho3+-Yb3+ doped LaNbO4 phosphors, which were synthesized for the first time by high-temperature solid-state reaction method. The LaNbO4:1Er3+:10Yb3+ and LaNbO4:1Ho3+:10Yb3+ phosphors exhibit reliable and excellent thermometric performance by combining fluorescence intensity ratio and decay lifetime for self-calibration. Specifically, the maximal relative sensitivities based on fluorescence lifetime were 0.27 %K−1 and 0.33 %K−1 for LaNbO4:1Er3+:10Yb3+ and LaNbO4:1Ho3+:10Yb3+ phosphors, respectively. The maximal relative sensitivity is 1.12 %K−1 when using intensity ratio between thermal coupling energy levels in LaNbO4:1Er3+:10Yb3+ as a detecting signal. Furthermore, the maximal relative sensitivity reaches as high as 0.98 %K−1 when taking advantage of special non-thermal coupling energy levels in LaNbO4:1Ho3+:10Yb3+. These results indicate that Er3+/Ho3+-Yb3+ doped LaNbO4 phosphors possess great potential in self-calibrated optical thermometric techniques.

Cubic-Shaped and Rod-Shaped YPO4 Nanocrystal-Doped Optical Fibers: Implications for Next Generation of Fiber Lasers

Engineering silica optical fibers by nanoparticle doping is a promising technology that allows the introduction of new functionalities and extends their applicable fields. However, the knowledge gap about the impact of the extreme fabrication temperatures on the nanoparticle features prevents field progress. Herein, we demonstrate that the particularities of fiber fabrication, such as fast-heating rates and quenching heat treatments, can be leveraged to explore unlikely phenomena at the nanoscale under standard laboratory conditions. Tetragonal cubic-shaped and monoclinic rod-shaped YPO4 nanocrystals are in situ nucleated in a silica-based fiber core glass, slightly modified with Ge and P, which shows for the first time, the possibility of doping optical fibers with this type of nanostructures, in terms of shape, composition, and structure of the nanocrystals. Structural and anisotropic differences allow engineering differently their shape and composition in the fiber core by tailoring the drawing temperature, as revealed by a thorough study consisting of scanning electron microscopy (SEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), electron energy loss spectroscopy (EELS), and high-resolution transmission electron microscopy (HRTEM). This work demonstrates, for the first time, the possibility of doping optical fibers fabricated by modified chemical vapor deposition (MCVD) with anisotropic nanostructures, as well as the stability of the monoclinic YPO4 phase. These findings open up new avenues to study shape-dependent properties of rare-earth orthophosphate (REPO4) nanostructures in optical fibers which will allow incorporating unprecedented functionalities and will have an impact in several fields of application, such as fiber lasers and optical fiber amplifiers, among others.

Mineralogical and Geochemical Constraints on the Occurrence Forms of REEs in Carboniferous Karst Bauxite, Central Guizhou Province, Southwest China: A Case Study of Lindai Bauxite

Karst bauxite is a major source of aluminum and contains high concentrations of trace elements such as Li, Ga, Sc, and rare earth elements (REEs). It is regarded as a potential non-conventional REE source due to the increasing demand for REEs. This study provides new mineralogical and geochemical evidence of a Lindai bauxite deposit in central Guizhou Province, aiming to analyze the genesis of REE minerals and reveal the forms of REEs occurring in these deposits. The results indicate that a large number of detrital and authigenic rare-earth phosphate minerals, including monazite and xenotime, were identified. In terms of their genesis, the authigenic monazite was mainly precipitated under alkaline and reducing conditions, whereas the authigenic xenotime was formed in acidic and reducing conditions. The mineralogical evidence detected by scanning electron microscopy with energy dispersive spectrometry (SEM-EDS) and a TESCAN Integrated Mineral Analyzer (TIMA) suggests that the REEs in the Lindai bauxite exhibit multiple forms, including rare-earth phosphate minerals (monazite and xenotime) and REE scavenging by hematite and anatase phases. Among them, the anatase controls some LREE (such as La, Ce, and Pr) distributions in addition to monazite, whereas the hematite also controls relatively large amounts of Sm, Eu, and HREE (such as Gd, Tb, Dy, Ho, Er, Tm, and Lu) distributions. According to the calculation of the percentage of REE-bearing mineral phases obtained by a TIMA analysis, REE scavenging by hematite accounted for 93.28% of all forms of REEs, REE scavenging by anatase accounted for 5.88%, monazite accounted for 0.67%, and xenotime accounted for 0.17%. This study provides new evidence of the forms of REEs occurring in Carboniferous karst bauxite in central Guizhou Province.

Defects and Persistent Luminescence in Eu -Doped SrAl 2 O 4

We investigate native point defects and rare-earth (co)dopants in SrAl$_2$O$_4$ using hybrid density-functional defect calculations. Europium (Eu) and dysprosium (Dy) are found to be mixed valence and energetically most favorable at the Sr lattice sites. However, unlike Eu where both Eu$^{2+}$ and Eu$^{3+}$ can be realized in synthesis, Dy is stable predominantly as Dy$^{3+}$, and the divalent Dy$^{2+}$ may only be photogenerated under irradiation. On the basis of an analysis of Eu-related band-defect (including charge-transfer) and interconfigurational $5d$-$4f$ optical transitions, we assign the characteristic broad blue (445 nm) and green (520 nm) emission bands in Eu$^{2+}$-doped SrAl$_2$O$_4$ to the $4f^65d^1$ $\rightarrow$ $4f^7$ transition in Eu$^{2+}$ incorporated at the Sr1 and Sr2 sites, respectively. Strontium interstitials (not oxygen vacancies, in contrast to what is commonly believed) and Dy$_{\rm Sr}$ can act as efficient electron traps for room-temperature persistent luminescence. This work calls for a re-assessment of certain assumptions regarding specific carrier trapping centers made in all mechanisms previously proposed for the persistent luminescence in Eu- and (Eu,Dy)-doped SrAl$_2$O$_4$. It also serves as a methodological template for the understanding and design of rare-earth doped phosphors.

Evidence of rare earth elements origin in acid mine drainage from the Iberian Pyrite Belt (SW Spain)

Acid mine drainage (AMD) is a worldwide pollution problem of watersheds. In addition to toxic metal(oid)s and acidity, many elements of economic interest are released into the environment, which make AMD a potential strategic secondary source of these elements such as rare earth elements (REE). Despite the importance of these metals, their origin in AMD is still uncertain. Recent hypotheses suggest preferential leaching of REE-enriched minerals as a possible source. Leaching tests with H2SO4 have been developed to simulate the interaction under AMD formation conditions with sulfide bodies and host rocks from two representative mining areas in the Iberian Pyrite Belt: the Perrrunal and Poderosa mines (SW of Spain). The REE patterns and Ce and Eu anomalies of the rock leachates have confirmed the geochemical relationship between the AMD and certain country rocks (felsic and mafic volcanics, and shales). A detailed chemical and mineralogical study has confirmed the existence of a diversity of minerals with high concentrations of REE. Thus, the minerals with the highest REE contents are also those with the fast dissolution kinetics under acid conditions: REE phosphates (monazite and xenotime type) and carbonates (parisite type). Finally, petrographic evidence of the selective leaching of these minerals clearly supports these minerals as the main source of REE in the AMD.

Interstitial Zinc Boosted Light Tunability, Afterglow, and Ultrabright White Emission in Zinc Germanate (Zn2GeO4)

To reduce the burden of solid-state lighting and phosphor-converted light-emitting diode technologies on rare earth (RE) and avoid their potential supply risks, we have developed a RE-free Zn2GeO4 (ZGeO) microcrystalline phosphor. It was synthesized by a simple and scalable solid-state reaction of ZnO and GeO2 at 1200 °C. High-temperature synthesized ZGeO demonstrated color tunable emission from bluish-white to green on changing the excitation wavelength from 265 to 335 nm with a photoluminescence quantum yield of 42 and 9%, respectively. They could also convert highly energetic X-ray to bluish-green light emission. First-principles calculations showed that bluish-white and green light emissions are linked to zinc interstitials present, respectively, in zinc (Zni2) and zinc–germanium rings (Zni1). These defects generated in large numbers via high-temperature annealing along with antisites boosted the generation of trapping centers leading to dual persistent luminescence (PerL) of white and green light for more than 60 min as well as exhibited radioluminescence. Luminescent ink based on ZGeO was fabricated and successfully tested for anticounterfeiting applications. An extra effort has been vested on making this solid-state processed ZGeO dispersible in water-soluble deep eutectic solvent which could be a game changer for its marketability. This material has great potential to become an efficient RE and dopant-free phosphor synthesized by a simple, scalable, and cost-efficient route for applications in solid-state lighting, display, and anticounterfeiting, having multifunctionalities such as PerL, tunability, and RL.

Gamma-Ray Sensing Properties of Nd Doped Phosphate Glasses

Five selected Nd2O3 doped phosphate glass compositions are synthesized using melt quench technique. The physical properties such as density (ρ) and molar volume (Vm) are experimentally measured. The density increases whereas molar volume decreases with addition of Nd2O3 content. The radiation sensing properties for these rare earth (RE) element doped phosphate glass samples have been investigated. The photon attenuation and sensing parameters such as mass attenuation coefficient (μm), linear attenuation coefficient (μL), optimum thickness range (x opt), effective atomic number (Zeff), and mean free path (mfp) values are computed over wide gamma-ray energy range 1keV -100 GeV within framework of WinXCom software tool. The photon sensing properties of these rare earth doped phosphate glasses vary significantly on account of neodymium oxide content and photon energy. The mean free path (mfp) values of glass samples are found to decrease while the mass attenuation coefficient values rise as Nd2O3 concentration does.

Rare Earth Element‐Based Recovery Concept for Cofactors Containing Phosphate Groups from Aqueous Solutions

AbstractCofactors, which are key components in many bio‐based processes, are often consumed within the biosynthetic reaction, but are usually converted back to their original form by recycling. This study presents an approach for the selective removal of cofactors from aqueous solution at up to submillimolar concentrations. The rare earth elements (REE) scandium, yttrium, and lanthanum, in the oxidation state +3, are used to form sparingly soluble salts with the investigated cofactors, pyridoxal‐5‐phosphate, NAD+, NADP+, adenosine triphosphate, and thiamine pyrophosphate. Up to &gt; 99 % removal efficiency via cofactor salt precipitation was observed. Redissolution and recovery of the formed salt is obtained via treatment with NaH2PO4 in a salt metathesis reaction, forming the solubilized cofactors with up to &gt; 99 % recovery and the corresponding REE phosphate salts.

Phase Transformation Pathway of DyPO4 to 21.5 GPa

Interest in the deformation behavior and phase transformations of rare earth orthophosphates (REPO4s) spans several fields of science—from geological impact analysis to ceramic matrix composite engineering. In this study, the phase behavior of polycrystalline, xenotime DyPO4 is studied up to 21.5(16) GPa at ambient temperature using in situ diamond anvil cell synchrotron X-ray diffraction. This experiment reveals a large xenotime–monazite phase coexistence pressure range of 7.6(15) GPa and evidence for the onset of a post-monazite transformation at 13.9(10) GPa to scheelite. The identification of scheelite as the post-monazite phase of DyPO4, though not definitive, is consistent with REPO4 phase transformation pathways reported in both the experimental and the computational literature.

Preparation and properties of NaLa(WO4)2:0.08Eu3+ phosphors

In the environment of advocating low-carbon economy, the development of green lighting and the potential application of rare earth luminescent light sources have always attracted much attention. In this study, aiming at the existing defects of white LED, taking the new red rare earth phosphor excited by ultraviolet light as the research object, Eu3+ doped NaLa(WO4)2:0.08Eu3+ phosphors samples were prepared by microwave method. The prepared samples were characterized by x-ray diffraction (XRD), scanning electron microscope (SEM), fluorescence spectrum (PL), CIE color coordinates and other detection methods, and their phase composition, micro-morphology and luminescent properties were characterized. The results show that the doping of Eu3+ does not change the crystal structure of the matrix material, and the NaLa(WO4)2:0.08Eu3+ phosphors is micron-sized and irregular polyhedral at room temperature. It can be excited by ultraviolet light with wavelength of 395 nm to produce red light emission. The color coordinates of NaLa(WO4)2:0.08Eu3+ phosphors are (0.5794, 0.308), and the manufactured device can emit white light with color coordinates of (0.3060, 0.3307). Therefore, the NaLa(WO4)2:0.08Eu3+ red phosphors prepared in this study is expected to be used in the preparation of white LED devices.

Photoluminescence and mixed-valence tuning of Eu in Sr2(Al,Ga)2SiO7 phosphors for sensitive thermometric applications

The regulation on chemical components is a valid way to develop rare earth doped phosphors of well-luminescent performances. In this work, the photoluminescence and mixed valences of Eu2+/3+ in Sr2(Al, Ga)2SiO7 can be tuned by Ga3+ regulation. The site-dependent luminescence of Eu2+ in Sr2(Al, Ga)2SiO7 are discussed on the basis of VUV-UV–vis spectra. With the gradual replacement of Ga3+ ions, both the ratio of Eu3+ contents and the proportion of Eu3+ emission increase with respect to that of Eu2+. Ab initio calculation and simulation of X-ray photoelectron spectra (XPS) are adopted to get deep insight. It was found that the increase ratio of Eu3+ to Eu2+ is mainly due to the decrease of band gap and fermi level. As results, emission color of Sr2(Al, Ga)2SiO7: Eu2+/3+ is tunable with different replaced Ga3+ contents, wavelengths and temperatures. Series of temperature-dependent measurements indicate that the Eu2+/ Eu3+ ratiometric emission can sensitively denote the variation of temperature under excitation at 300 nm. After the fine-modification by Ga3+, Sr1.9Eu0.1Al1.9Ga0.1SiO7 phosphor shows sensitive temperature readout.

Evidence of thermal ionization induced luminescence quenching in CePO4 and GdPO4

The optical properties and their temperature dependence of two rare earth orthophosphates, CePO4 and GdPO4, are presented.

Development trends of rare-earth luminescence: A bibliometric analysis

Rare-earth phosphors are gaining widespread attention due to their extensive applications from basic applied sciences to commercial hi-tech devices. The research publications on these materials are increasing exponentially and it is the need of the hour to analyze this particular topic statistically. This study aims to perform bibliometric analysis on 1315 documents published between 1971 and 2022 on scopus and web of science databases. The identified documents were examined and visualized using biblioshiny app of bibliometrix-R package. Ever upsurging growth in annual productions deciphers the significance of these phosphors. In terms of number of publications and Bradford’s law ‘Journal of luminescence’ and ‘Journal of alloys and compounds’ are identified as leading core sources whereas as per h-index criteria Nanoscale and Biomaterials are the high impact journals. Keyword analysis, cluster mapping and thematic mapping suggest that up-conversion nanophosphors is a growing field and the string connecting the basic sciences with biological applications of rare-earths has yet to be strengthened.

Photoluminescence behavior of rare earth doped self-activated phosphors (i.e. niobate and vanadate) and their applications.

In the present study, the photoluminescence behaviors of rare earth doped self-activated phosphors are discussed briefly. Different techniques were used to develop these phosphor samples. We prepared pure and rare earth doped phosphor samples to look for their various applications. The structural confirmations and surface morphologies were performed using X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements, respectively. The upconversion (UC) phenomenon was investigated in Tm3+/Yb3+ and Ho3+/Yb3+ co-doped niobate and vanadate based phosphors, which gave intense blue/NIR and green/red emissions with a 980 nm diode laser as an excitation source. Pure niobate and vanadate phosphor materials are self-activated hosts which give broad blue emission under UV excitation. Upon UV excitation, intense broad blue emission along with sharp emissions due to Tm3+ and Ho3+ ions are observed via energy transfer between niobate/vanadate and rare earth ions. These self-activated hosts show prominent downshifting (DS) behavior. Broad band quantum cutting (QC) was observed in these self-activated hosts, in which a blue emitting photon is converted into two NIR photons by co-doping Yb3+ ions in it. The multimodal (upconversion, downshifting and quantum cutting) behaviors of these phosphors make them very promising in various applications, such as spectral converters to enhance the efficiency of a c-Si solar cell, security ink and color tunable materials.

Systematic regulation of ligands realizes the transition of luminescence color cuprous iodide inorganic–organic hybrid materials from blue to green light

Four AIO-structured cuprous iodide hybrids were synthesized, with modifying the tail atoms of ligand. They all show strong luminescence, stable and good solution processability. They can be applied as rare-earth element-free lighting phosphors.

Self-activated rare-earth free phosphor prepared by propylene glycol-modified silane

A facile wet-chemistry method can be applied to produce efficient rare-earth-free LED phosphors. In this study, self-activated Ca2SiO4 phosphor was developed using a propylene glycol-modified silane (PGMS) as a silicate source. The structural and luminescence properties of samples were characterized using synchrotron X-ray powder diffraction and photoluminescence (PL) spectroscopy, respectively. The PGMS phosphor consists of mixed crystal phases of α′L, β, and γ, whereas the solid-state reaction (SSR) phosphor only has a β phase. The synthesized PGMS phosphor with distinctive crystal defects shows self-activated luminescence, while the SSR phosphor has no PL properties.