Rare Earth Phosphates Research Articles

Inorganic halide perovskites for lighting and visible light communication

Inorganic halide perovskites (IHPs) have received substantial attention due to their unique optoelectronic properties. Among all the intriguing performance, the efficient luminescence of IHPs enables the practical application of white light-emitting diodes (WLEDs) for lighting. During the last decade, IHP-based white lighting sources with a high luminesce and a broad color gamut have been developed as strong competitors to conventional and classic WLEDs based on rare-earth phosphors and blue LED chips. Thus, it inspires us to give an overview of the emerging progress of IHP WLEDs that can function as lighting sources. Here, in this review, the generation of luminescent properties and white light in IHPs are first presented. Then, both photoluminescence and electroluminescence WLEDs with IHPs emitters, including both lead-based and lead-free IHPs, are synthetically discussed to exhibit their advantages. Furthermore, the efforts on the optical performance enhancement of IHPs in WLEDs are demonstrated and summarized. Apart from WLEDs, visible light communication based on IHPs featuring efficient luminescence is proposed to highlight their promising potential in lighting communication. Finally, some perspectives on the evolution and challenges are described, followed by an inspirational outlook on their future development.

MxLa1–xSiO2–yNz (M = Ca/Sr/Ba): Elucidating and Tuning the Structure and Eu2+ Local Environments to Develop Full-Visible Spectrum Phosphors

The local environments of rare-earth activators have profound effects on the luminescent properties of phosphors. Here, we elucidate the crystal structure of the LaSiO2N phosphor host using a combination of density functional theory calculations and synchrotron X-ray diffraction. We determine that LaSiO2N crystallizes in the monoclinic C2/c instead of the hexagonal P6̅c2 space group. To improve the luminescence performance, divalent cations M (M = Ca/Sr/Ba) were introduced into LaSiO2N to eliminate Eu3+. A family of apatite M1+xLa4–xSi3O13–x/2:Eu2+ (x ∼ 1.5, M = Ca/Sr/Ba) phosphors was further developed with unprecedented ultra-broadband (290 nm) emission spectra and excellent thermal stability. Detailed local environment investigations reveal that the formation of oxygen vacancies within and beyond the first-shell environment of Eu2+ is responsible for the redshift and broadening of the emission spectra via geometrical alteration of the Eu2+ local environment. This work provides new insights for understanding and optimizing the luminescence of rare-earth phosphors.

PEG coated nano-phosphor GdPO4•H·H2O:12%Eu3+ and its performance analysis

The surface modification and performance analysis of the nano-phosphor GdPO4·H2O:12%Eu3+ were carried out in this study. Since the rare earth phosphate is hydrophobic, its applications in the fields of biology and medicine are greatly restricted. In order to solve this problem, the microwave method was adopted for surface modification with PEG as the modifier in this paper, and the nano-phosphor GdPO4·H2O:12%Eu3+@PEG with excellent performance and a core-shell structure was prepared. XRD, SEM, TEM, FTIR, TG-DSC, FL and VSM were used to characterize the structure, morphology, optical and magnetic properties of the phosphor before and after modification. The results show that the nano-phosphor GdPO4·H2O:12%Eu3+ and GdPO4·H2O:12%Eu3+@PEG had the same structure, that is, a single hexagonal crystal structure. The morphology of the products before and after PEG coating was short rod; the agglomeration phenomenon was weakened after coating; and the thickness of the coating layer was about 10 nm. The positions of the excitation and emission peaks before and after coating did not move, but the fluorescence intensity increased by about 2–3 times; and the fluorescence lifetime increased by 0.2–0.3 ms. When the coating amount of PEG was 0.3000 g, the fluorescence intensity of GdPO4·H2O:12%Eu3+ was the highest. The color coordinates were basically the same before and after coating. The magnetic properties were basically unchanged, and the magnetization intensity was all 1.75 emu/g. The hydrophilicity and biocompatibility of the nano-phosphor GdPO4·H2O:12%Eu3+ were successfully solved in this paper, its luminescent properties were improved, and its magnetic properties were maintained.

Near-UV excited green-emission enhancement by efficient energy transfer in Na1.8Mg0.9Si1.1O4:Ce3+,Tb3+ phosphor for solid-state lighting applications

Luminescence properties of phosphor play a key role in the performance of white light-emitting-diodes (LEDs). The Tb3+ emission under near-UV excitation is usually very weak due to f-f spin-forbidden transitions. In this paper, we report that Tb3+ emission under near-UV excitation enhances up successfully in Ce3+,Tb3+ co-doped Na1.8Mg0.9Si1.1O4 (NMSO) phosphor, as a result of efficient energy transfer from Ce3+ to Tb3+. The newly-prepared NMSO:Ce3+,Tb3+ exhibits a strong green-emission line at λmax = 545 nm under 340 nm excitation, and the quantum efficiency is 0.82. The maximum energy transfer efficiency is up to 92.3%. The good thermal quenching resistance, high color-rendering index Ra (91.5) and low CCT (4752 K) of the packaged white LED demonstrate that energy transfer of rare earth phosphors is an effective strategy to target tailored optical performance. NMSO:Ce3+,Tb3+ phosphor has potential applications in near-UV chip excited white LEDs as a green-emitting component.

Simultaneous Spectral Tuning and Thermal Stability Adjustment in Ca8ZnGa(1-x)Lax(PO4)7:Eu2+ Phosphors.

The modifications of local structure in solid solution are a crucial step to regulate the photoluminescence properties of rare-earth ion-based phosphors. However, the structural diversity of host matrices and the uncertain occupation of activators make it challenging to obtain phosphors with both high stability and tailored emission. Herein, We synthesized a series of β-Ca3(PO4)2-type Ca8ZnGa(1-x)Lax(PO4)7:Eu2+ solid solution phosphors by design. By modifying the Ga/La ratio, controllable regulation of the emission spectrum and thermal stability of the phosphors can be achieved at the same time. The introduction of La3+ can regulate the crystal field splitting strength of the Eu2+ activators, causing redshifts in the emission spectrum while increasing Ga3+ content will lead to enhanced energy transfer between the oxygen vacancy and Eu2+, as well as improved thermal stability. Through local structure modification, the spectrum and thermal stability of phosphors can be facilely tuned. The results indicate that this series of phosphors have versatile potentials in various applications.

Recovery of Light Rare Earth Elements (LREE) from Monazite by Alkaline Fusion

Malaysia has many potential mineral resources including some rare earth elements (REE) minerals such as monazite. REE play critical roles in the applications of advanced materials. Alkaline fusion was introduce to monazite to break the bonding between Light Rare Earth Elements (LREE) and phosphate. In this study, critical parameter such as fusion temperature (100 °C to 250 °C) and duration (1 to 4 hours) were studied. The results shows that it is possible to recover nearly 100% of Neodymium after 2 hours fusion at 150 °C. In the other hand, more than 99% of Cerium and Lanthanum were recovered after 3 hours fusion at similar temperature. By recover most of the element, expectantly high yield of single LREE can be achieved in the forthcoming.

Crystal chemistry and miscibility of chernovite-(Y), xenotime-(Y), gasparite-(Ce) and monazite-(Ce) from Mt. Cervandone, Western Alps, Italy

AbstractThe crystal chemistry and crystal structure of the rare earth element phosphates, monazite-(Ce), Ce(PO4), and xenotime-(Y), Y(PO4), as well as the arsenates, gasparite-(Ce), Ce(AsO4), and chernovite-(Y), Y(AsO4), from the hydrothermal quartz-bearing fissures, related to pegmatites overprinted by amphibolite facies, cropping out at Mt. Cervandone, Western Alps, Piedmont, Italy, have been investigated by means of electron microprobe analysis in wavelength dispersion mode and single-crystal X-ray diffraction. The chemical data reveal the occurrence of a full solid solution among the isostructural chernovite-(Y) and xenotime-(Y) with tetragonal symmetry, whereas a wide miscibility gap is observed for the isostructural gasparite-(Ce) and monazite-(Ce) of Mt. Cervandone, with monoclinic symmetry. A significant chemical heterogeneity has been observed for several investigated samples, especially related to the Th content, which is locally enriched in ThSiO4 grains. The analysis of the refined structural models demonstrates the significant control played by the composition of the tetrahedrally-coordinated (As,P)-bearing sites on the bulk unit-cell volume, and on the size and shape of the (REE)-coordination polyhedra.

The pH Value Control of Morphology and Luminescence Properties of Gd2O2S: Tb3+ Phosphors.

Developing rare-earth doped oxysulfide phosphors with diverse morphologies has significant value in many research fields such as in displays, medical diagnosis, and information storage. All of the time, phosphors with spherical morphology have been developed in most of the related literatures. Herein, by simply adjusting the pH values of the reaction solution, Gd2O2S:Tb3+ phosphors with various morphologies (sphere-like, sheet-like, cuboid-like, flat square-like, rod-like) were synthesized. The XRD patterns showed that phosphors with all morphologies are pure hexagonal phase of Gd2O2S. The atomic resolution structural analysis by transmission electron microscopy revealed the crystal growth model of the phosphors with different morphology. With the morphological change, the band gap energy of Gd2O2S:Tb3+ crystal changed from 3.76 eV to 4.28 eV, followed by different luminescence performance. The samples with sphere-like and cuboid-like microstructures exhibit stronger cathodoluminescence intensity than commercial product by comparison. Moreover, luminescence of Gd2O2S:Tb3+ phosphors have different emission performance excited by UV light radiation and an electron beam, which when excited by UV light is biased towards yellow, and while excited by an electron beam is biased towards cyan. This finding provides a simple but effective method to achieve rare-earth doped oxysulfide phosphors with diversified and tunable luminescence properties through morphology control.

Anti-thermal quenching of Eu3+ luminescence in negative thermal expansion Zr(WO4)2

Thermal quenching of luminescence is the most critical problem for rare earth doped phosphors used in light-emitting diodes (LEDs). Herein, we demonstrate that thermal quenching can be considerably suppressed via the negative thermal expansion effect in Zr(WO4)2 that serves as host for Eu3+ red emission. The photoluminescence (PL) intensity is surprisingly enhanced by 130% when the temperature is raised from room temperature to 100 °C. As temperature further increases to 160 °C, the PL intensity turns to reduce, which is still 1.4 times of that at room-temperature. Moreover, Zr(WO4)2:15%Eu phosphor has good durability, which still exhibits strong red luminescence (only 13% loss) after being kept in 85 °C/85% relative humidity chamber for 240 h. The anti-thermal quenching of Eu3+ luminescence can be ascribed mainly to the following two factors: first one is the thermal-enhanced energy transfer between Eu3+ ions induced by the contraction of Zr(WO4)2 unit-cell volume that leads to the strong structural rigidity of host lattice; second one would be electron traps in the host that favors the increase of electrons on the excited energy levels. This important anti-thermal quenching effect induced from the negative thermal expansion of the host matrix may stimulates a novel and efficient approach to design highly thermal stable phosphors for next-generation LEDs.

Environmentally benign rare earth pigments: effect of calcium dopant and tuning of bandgaps for different color hues

PurposeAs there is a strong inducement to develop new colored inorganic materials to substitute the current industrial pigments that are based on toxic metals hazardous to health and the environment, the purpose of this paper is to invent environmentally benign rare earth-based colorants as viable alternatives to the traditional toxic pigment formulations. Herein, the authors developed a series of rare earth pigments having the general formula Ca0.1 Ln0.9 PO4 ( Ln = Y , Pr , mixed rare earth oxides, RE and Di). After studying all the optical properties, the authors have gone for some coloring application in plastic like PMMA.Design/methodology/approachThe designed pigments were synthesized by traditional solid-state method. Stoichiometric amounts of each reagent were mixed in an agate mortar and the mixtures were calcined at optimized temperature 1000 °C for 4 h in electric furnace followed by auto–cooling. The samples were characterized by X-ray diffraction diffraction, UV–vis spectroscopy, scanning electron microscope (SEM), particle size distribution, color coordinates determination, acid/alkali test, thermo gravimetric (TG) analysis and CIE–1976 L*a*b* color scales. Among the various lanthanide ions and calcium ion as dopant, the pigment composition shows various hues ranges from green to yellow. The designed pigments consist of non–toxic elements and were further found to possess high thermal and chemical stability. The pigments were also found to be appropriate candidates for the coloration of polymer substrates like PMMA.FindingsThe present investigations establish that various color hues can be achieved by the incorporation of suitable chromophore metal ions like calcium in various rare earth host lattice by tuning of the band gaps. The coloring mechanism is based on the strong absorption of the pigments in the blue and red regions due to electronic transitions of the micro states of rare earth ion. The pigment composition shows various hues ranges from green to yellow. The coloring mechanism is based on the tuning of band gap by the dopant like calcium in various rare earth host lattice. In addition, this pigment was chemically and thermally stable. Finally, it has applied in plastics like PMMA.Research limitations/implicationsMechanism of the color appearance using band calculations and on possible applications of rare earth phosphate powders as pigments in plastics and paints have not been explored much. However, the properties of the Ca-doped rare earth phosphate implies that this material has a potential to be applied as a satisfactory pigment for coating or coloring except for glaze, which may cause a side reaction at high temperatures, especially taking into consideration the economics and ecologies. The possibility of Ca2+ incorporation in CePO4 with monazite structure-type has been established.Practical implicationsThe designed pigments consist of non-toxic elements and were further found to possess high thermal and chemical stability. The pigments were also found to be appropriate candidates for the coloration of polymer substrates. Thus, the present environmental friendly pigment powders may find potential alternative to the classical toxic inorganic pigments for various applications.Social implicationsThere is a strong incentive to design new colorants based on inorganic materials to substitute for industrial pigments that are based on heavy elements hazardous to health and the environment. However, several industrial yellow pigments such as cadmium yellow (CdS), chrome yellow (PbCrO4) and nickel titanium yellow (TiO2-NiO-Sb2O3) contain the harmful elements (e.g. Cd, Pb, Cr and Sb) for the human body as well as the environment. The designed pigments consist of non-toxic elements and were further found to possess high thermal and chemical stability. The pigments were also found to be appropriate candidates for the coloration of polymer substrates. Thus, the present environmental friendly pigment powders may find potential alternative to the classical toxic inorganic pigments for various applications.Originality/valueThere is a strong incentive to design new colorants based on inorganic materials to substitute for industrial pigments that are based on heavy elements hazardous to health and the environment. However, several industrial yellow pigments such as cadmium yellow (CdS), chrome yellow (PbCrO4) and nickel titanium yellow (TiO2-NiO-Sb2O3) contain the harmful elements (e.g. Cd, Pb, Cr and Sb) for the human body as well as the environment. So, the authors have developed new class of inorganic pigments that are both non-toxic and environmentally unimpeachable, while preserving or even exceeding the optical, thermal and chemical characteristics of the existing commercial pigments. The developed colorants find practical applications in polymer matrix like PMMA.

Design a rare-earth free broadband NIR phosphor and improve the photoluminescence intensity by alkali charge compensation

Near-infrared (NIR) phosphors, promising non-destructive measurement materials for food, have attracted extensive attention worldwide. Herein, we designed a low-cost rare-earth free Mg2B2O5:Cr3+ phosphor. Under the excitation of 450 nm, the Mg2B2O5:Cr3+ phosphors show a broadband near-infrared emission at 800 nm, for 4T2 (4F) → 4A2 transition. The optimal concentration of Cr3+ was about 0.003 and a higher concentration will lead to concentration quenching owing to dipole-dipole interaction. Moreover, considering the unequal substitution of Mg2+ by Cr3+, charge compensation had been applied to improve the photoluminescence. The mechanism of alkali charge compensation and its effect on polyhedron distortion had been illustrated. The relationship between decay lifetime and charge compensation had been discussed. Finally, the activation energy for thermal quenching of as-prepared samples was calculated. The increasing polyhedron distortion result in worse thermal stability, which was explained by the configurational coordinate model. The above results are helpful in the development of low-cost near-infrared phosphors and the enhancement of photoluminescence intensity.

Synergistic use of Raman and photoluminescence signals for optical thermometry with large temperature sensitivity

In this work we demonstrate that large temperature sensitivity over a wider temperature range is possible by adopting the dual use of Raman and photoluminescence (PL) signals emitted by rare-earth doped crystalline phosphors when excited by a suitable laser light. We define Raman-PL-intensity ratio (RPIR) as an alternative thermometric parameter to define temperature sensitivity and exploited the contrasting effect of temperature on the intensities of the PL and Raman lines of a Eu3+-doped BaTiO3 ferroelectric phosphor and achieved large temperature tuning of color (red ↔ blue/green) and large relative temperature sensitivities in a wide temperature range: +6.4 %K−1 at 65 K, +2.4 %K−1 at 303 K. Our strategy offers greater flexibility for the design of phosphor systems for optical thermometry with high sensitivity.

Dissolution kinetics of rare earth metal phosphates in carbonate solutions of alkali metals

Treatment of apatite raw materials is associated with the formation of large-tonnage waste – phosphogypsum. The content of rare earth metals in such waste reaches 1 %, which makes it possible to consider it a technogenic source for obtaining rare earth metals and their compounds. Up to the present moment, there are neither processing plants, nor an efficient process flow to handle phosphogypsum dumps. It is rational to use a way that involves extraction of valuable components and overall reduction of phosphogypsum dumps. Such process flow is available with carbonate conversion of phosphogypsum to alkali metal or ammonium sulfate and calcium carbonate upon the condition of associated extraction of rare earth metal (REM) compounds. Associated extraction of REM compounds becomes possible since they form strong and stable complexes with hard bases according to Pearson, which among other things include carbonate, phosphate and sulfate anions. Formation of lanthanide complexes with inorganic oxygen-containing anions is facilitated by the formation of high-energy Ln-O bonds. The study focuses on the dissolution of lanthanide phosphates in carbonate media. It was established that formation of REM carbonate complexes from their phosphates is a spontaneous endothermic process and that formation of lanthanide carbonates and hydroxides serves as thermodynamic limitation of dissolution. A shift in equilibrium towards the formation of carbonate complexes is achieved by increasing the temperature to 90-100 °C and providing an excess of carbonate. The limiting stage of REM phosphate dissolution in carbonate media is external diffusion. This is indicated by increasing rate of the process with an intensification of stirring, first order of the reaction and the value of activation energy for phosphate dissolution from 27 to 60 kJ/mol. A combination of physical and chemical parameters of the process allowed to develop an engineering solution for associated REM extraction during carbonate conversion of phosphogypsum, which included a 4-5 h conversion of phosphogypsum at temperature of 90-110 °C by an alkali metal or ammonium carbonate solution with a concentration of 2-3 mol/l. As a result, a solution with alkali metal (ammonium) sulfate is obtained, which contains REMs in the form of carbonate complexes and calcium carbonate. The rate of REM extraction into the solution reaches no less than 93 %. Rare earth metals are separated from the mother liquor by precipitation or sorption on anion exchange resins, while the excess of alkali metal or ammonium carbonate is returned to the start of the process.

A review study on the structural and photoluminescence properties of rare earth doped lanthanate ALa2ZnO5 (A = Ca, Sr or Ba) phosphors

Rare earth doped phosphors are gaining much more attention attributed to their wide optoelectronic applications in the solid-state lighting, in fluorescent lamps, solar cells, display devices, temperature sensors etc. The structural and photoluminescent (PL) features of rare earth doped lanthanate compounds ALa2ZnO5 (A = Ca, Sr or Ba) are extensively explored by researchers owing to their better physical, chemical and luminescent properties. This review deals with the study of different methods used for the synthesis of bare and rare earth doped ALa2ZnO5 (A = Ca, Sr or Ba) phosphors. The solution combustion process has proved to be a better low temperature synthesis technique than the alternative methods such as solid state, sol-gel and co-precipitation methods etc. to get highly crystalline lanthanate phosphors. Structural analysis is also studied in detail to understand the different phases of rare earth doped CaLa2ZnO5, SrLa2ZnO5 and BaLa2ZnO5 phosphors. Apart from this, the PL properties of these rare earth doped lanthanate compounds are explained in depth. Their excitation, emission wavelength, lifetime and CIE coordinates are also provided for comparative studies along with their applications. Owing to the significant number of energy transitions of rare earth ions within the host lattice, these lanthanate phosphors have wide scope in different display fields. The reading of this review will be beneficial for researchers working in the field of phosphors.

Development of Mechanically Reliable and Transparent Photochromic Film Using Solution Blowing Spinning Technology for Anti-Counterfeiting Applications.

Photochromic materials have attracted broad interest to enhance the anti-counterfeiting of commercial products. In order to develop anti-counterfeiting mechanically reliable composite materials, it is urgent to improve the engineering process of both the material and matrix. Herein, we report on the development of anti-counterfeiting mechanically reliable nanocomposites composed of rare-earth doped aluminate strontium oxide phosphor (RESA) nanoparticles (NPs) immobilized into the thermoplastic polyurethane-based nanofibrous film successfully fabricated via the simple solution blowing spinning technology. The generated photochromic film exhibits an ultraviolet-stimulated anti-counterfeiting property. Different films of different emissive properties were generated using different total contents of RESA. Transmission electron microscopy was utilized to investigate the morphological properties of RESA NPs to display a particle diameter of 3–17 nm. The morphologies, compositions, optical transmittance, and mechanical performance of the produced photochromic nanofibrous films were investigated. Several analytical methods were employed, including energy-dispersive X-ray spectroscopy, scanning electron microscopy, and Fourier-transform infrared spectrometry. The fibrous diameter of RESA-TPU was in the range of 200–250 nm. In order to ensure the development of transparent RESA-TPU film, RESA must be prepared in the nanosized form to allow better dispersion without agglomeration in the TPU matrix. The luminescent RESA-TPU film displayed an absorbance intensity at 367 nm and two emission intensities at 431 and 517 nm. The generated RESA-TPU films showed an enhanced hydrophobicity without negatively influencing their original appearance and mechanical properties. Upon irradiation with ultraviolet light, the transparent nanofibrous films displayed rapid and reversible photochromism to greenish-yellow without fatigue. The produced anti-counterfeiting films demonstrated stretchable, flexible, and translucent properties. As a simple sort of anti-counterfeiting substrates, the current novel photochromic film provides excellent anti-counterfeiting strength at low-cost as an efficient method to develop versatile materials with high mechanical strength to create an excellent market as well as adding economic and social values.

Unique capability of NdPO4 to activate hydrogen for efficient hydrogenation of furfural to furfuryl alcohol over Nd-Co-P composites

Efficient and applicable catalysts are highly desirable for advanced biomass transformation industry, here, we fabricated a series of Nd-Co-P catalysts for hydrogenation of furfural (FAL) to furfuryl alcohol (FOH). By comprehensive characterizations, it is demonstrated that the prepared Nd-Co-P samples are structured as (NdPO4)m/Co2P nanocomposites with molar ratio (m) in range of 0.24–1.1; by manipulating m, the outstanding catalytic efficiency comparable with the performance of precious metal catalysts, such as turnover frequency (TOF) up to 0.50 s−1 (being ten-fold higher than Co2P) and FOH yield up to 97%, is achieved on the reusable (NdPO4)m/Co2P composites. Temperature programmed desorption (TPD), in-situ infrared spectroscopy (IR) and kinetic-mechanism studies further disclose that Co2P is decisive for activating FAL, instead, NdPO4 possesses unique capability of activating hydrogen which readily facilitate the selective hydrogenation of FAL to FOH through a rapid Langmuir–Hinshelwood process over (NdPO4)m/Co2P catalyst. These results indicate that rare-earth phosphates like NdPO4 can act as the promising and reliable catalytic component to activate hydrogen, which can be of interest not only for innovating novel and applicable non-metallic catalysts for sustainable biomass transformation analogous to hydrogenation of FAL, but also for expanding material base for other green mass transformation techniques involving hydrogen.

Synthesis of rare-earth nanosized phosphors using microwave processing

Nanomaterials find permanently extending applications in various areas of life. In particular, nanosized phosphors can be used as pharmaceutical carriers capable of emitting ultraviolet or visible light that activates a photosensitizer, thus significantly expanding the possibilities of photodynamic therapy in the treatment of oncological, bacterial and viral diseases. The conditions required for the use of nanosized phosphors in medicine include their fine dispersion and effective luminescence in the red region of visible light spectrum upon stimulation by X-ray radiation of the range accepted for medical applications, particularly for diagnostic and therapeutic purposes in many diseases. The aim of this work was to study the effect of microwave treatment of Y2O3:Eu phosphors prepared by hydrothermal synthesis in ethylene glycol at 230 °C for 6 hours, involving the decomposition of mixed acetate. In order to reduce the aggregation and growth of the resulting particles, Aerosil A300 with average particle size 7 nm was added to the reaction mixture in the course of hydrothermal synthesis in the ratio 1:1 relating to the obtained phosphor. The microwave treatment was carried out at 800 °C for 5 minutes. The developed method provided Y2O3:Eu phosphor samples featuring with increased luminescence intensity in the region 610…700 nm compared to similar phosphors earlier prepared using the rapid thermal annealing (RTA) procedure.

Red emitting Eu3+ induced SrWO4 materials: synthesis, structural, morphological and photoluminescence analysis

Rare-earth doped phosphors have occupied significant percentage in the field of luminescence applications. In order to get the optimized intensity of PL spectra, the dopant selection, dopant concentration and preparation technique plays a major role. In this work, SrWO4 and Eu3+ doped SrWO4 were successfully synthesized via fuel assisted solid state reaction technique at a temperature of 900 °C. The effect of Eu concentration on SrWO4 was analyzed by X-ray diffraction, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and PL spectroscopy. All the diffraction peaks of prepared SrWO4 and Sr1−xEuxWO4 (x = 0.01, 0.02, 0.03, 0.04 and 0.05) were well-matched with the standard tetragonal phase of SrWO4. In the PL study, SrWO4:Eu3+ shows the characteristics emission peaks at 5D0 → 7FJ (J = 1, 2, 3, 4) transitions for Eu3+. 5D0 → 7F2 (615 nm) is predominant at 394 nm excitation wavelength. The PL emission intensity at 615 nm gradually increases upto 4% of Eu3+ and then decreases. Using XPS, the chemical state analysis was carried out in Sr1−xEuxWO4 (x = 0.04) and Eu dopant is in 3 + oxidation state. The electron density distribution analysis in the unit cell was carried using the maximum entropy method (MEM) and their charge derived properties were correlated with the PL analysis. Based on the different characterization analysis, Eu3+ doped SrWO4 act as an efficient red-emitting phosphor for Near UV (394 nm excitation), blue LED (450 nm excitation) based white LED and FED applications.

A spectral library for laser-induced fluorescence analysis as a tool for rare earth element identification

Abstract. With the recurring interest in rare earth elements (REEs), laser-induced fluorescence (LiF) may provide a powerful tool for their rapid and accurate identification at different stages along their value chain. Applications to natural materials such as minerals and rocks could complement the spectroscopy-based toolkit for innovative, non-invasive exploration technologies. However, the diagnostic assignment of detected emission lines to individual REEs remains challenging because of the complex composition of natural rocks in which they can be found. The resulting mixed spectra and the large amount of data generated demand automated approaches of data evaluation, especially in mapping applications such as drill core scanning. LiF reference data provide the solution for robust REE identification, yet they usually remain in the form of tables of published emission lines. We show that a complete reference spectra library could open manifold options for innovative automated analysis. We present a library of high-resolution LiF reference spectra using the Smithsonian rare earth phosphate standards for electron microprobe analysis. We employ three standard laser wavelengths (325, 442, 532 nm) to record representative spectra in the UV-visible to near-infrared spectral range (340–1080 nm). Excitation at all three laser wavelengths yielded characteristic spectra with distinct REE-related emission lines for EuPO4, TbPO4, DyPO4 and YbPO4. In the other samples, the high-energy excitation at 325 nm caused unspecific, broad-band defect emissions. Here, lower-energy laser excitation is shown to be successful for suppressing non-REE-related emission. At 442 nm excitation, REE reference spectra depict the diagnostic emission lines of PrPO4, SmPO4 and ErPO4. For NdPO4 and HoPO4 the most efficient excitation was achieved with 532 nm. Our results emphasise the possibility of selective REE excitation by changing the excitation wavelength according to the suitable conditions for individual REEs. Our reference spectra provide a database for the transparent and reproducible evaluation of REE-bearing rocks. The LiF spectral library is available at zenodo.org and the registered DOI https://doi.org/10.5281/zenodo.4054606 (Fuchs et al., 2020). Primarily addressing the raw material exploration sector, it aids particularly the development of advanced data processing routines for LiF analysis but can also support further research on the REE luminescence in natural rocks or artificial compounds. It gives access to traceable data for the comparison of emission line positions, emission line intensity ratios and splitting into emission line sub-levels or can be used as reference or training data for automated approaches of component assignment.

A TbPO4-based capturer for environmental extracellular antibiotic genes by interrogating lanthanide phosphates nanoneedles

Accurate determination of antibiotic resistance genes (ARGs) in environmental DNA molecules (eDNA) is challenging owing to its low abundance in the aquatic environment. Here we report a facile and cost-efficient approach to extract trace amount of eDNAs in the aquatic environment using LnPO4 nanomaterials. Among the nanomaterials, less crystalline TbPO4 nanoneedles was identified as the most prominent candidate for long stranded DNA and short stranded DNA with adsorption efficiency above 97%. The adsorbed DNA was washed off from TbPO4 nanoneedles by optimized eluant (85% PBS, 15% EtOH, 4 g/L glycine, pH 10.0) with an optimal DNA recovery of 78.83%. Our approach showed a comparable or better eDNA extraction efficiency than a commercial extraction method for different environmental samples, but 89% less cost. The high purity of the extracted eDNA was demonstrated by a high A260/280 ratio. Using qPCR experiment, the occurrence of six common ARGs in the eDNA were detected with abundance ranging from 4.06 × 103 to 3.51 × 109 copies/L in river samples. This specific DNA capturer is valuable for the evaluation of spatial and temporal dynamic of ARGs pollution to provide insight into the potential risk with regard to the human health.