Concentration Of Rare Earth Ions Research Articles

Refractive index of fluoride crystals doped with rare earth ions with low concentration

Refractive indices of SrF2 crystals doped with low concentrations of holmium, erbium, and thulium ions are investigated. These crystals are attractive as active laser media for developing planar waveguides for near and mid-IR spectral regions. It is shown that, by varying the concentration of impurity rare-earth ions in SrF2 crystals, it is possible to increase and control the refractive index of the medium. This allows one to develop planar waveguides with the core and shell of the same fluoride and control theirs numerical aperture and the number of excited modes. The design of single mode planar waveguide is calculated and proposed for the wavelength of 2 um.

Behavior and mechanism of low-concentration rare earth ions precipitated by the microbial humic-like acids.

The disposal of bulky low-concentration rare earth solutions (usually ≤ 200mgL-1) is difficult and it can easily lead to the waste of rare earth resources. The precipitant separation method is a simple and effective technique that is commonly used for rare earth recovery, but the application of biological component precipitants is rarely reported. In this study, the effects of the precipitation of low concentrations of rare earth ions by excess sludge humic-like acids were evaluated. Scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS) and infrared (IR) spectroscopy revealed that the addition of humic-like acids to low-concentration rare earth solutions could produce a flocculent precipitate. The precipitation rate was more than 89%. The content of rare earth metals such as Nd, Y, and La in the rare earth precipitate reached 23.72%, and the elution rate of 1.25molL-1 hydrochloric acid was 90.50%. It was concluded that the humic-like acids might contain many functional groups capable of adsorbing rare earth ions. It was inferred that the possible mechanism might be that rare earth ions were precipitated by a series of net catch, ion exchange, and adsorption processes. These findings provide a reference for the future recovery of rare earth resources.

Up-conversion luminescence and energy transfer mechanism in ZnTiO3: Er3+,Yb3+ phosphor

Er3+ and Yb3+ doped zinc titanate (ZnTiO3) was successfully synthesized using the conventional solid-state reaction method. X-ray diffraction confirmed crystallization of an ecandrewsite ZnTiO3 of an undoped sample, although impurity phases from the dopants were present in the doped and co-doped samples. The surface analysis showed a morphology composed of agglomerated irregular shaped particles. The energy band gap of ZnTiO3 was affected by the incorporation of different concentrations of rare-earth dopant ions. After irradiating the ZnTiO3:Er3+,Yb3+ phosphors with a 980 nm laser beam, the phosphor displayed up-converted photoluminescence emission in the visible range of the electromagnetic spectrum. The emission mostly consisted of green and red bands of Er3+ ions with peaks located at 527, 545 and 665 nm. Co-doping with Yb3+ ions proved effective in enhancing the luminescence intensity of the Er3+ ion emission, through an energy transfer mechanism.

A two-parameter model for ion exchange process of ion-adsorption type rare earth ores

The establishment of a mathematical model for the ion exchange process is key to creating a theoretical basis for the mining of ion-adsorption type rare earth ores. Ore samples from Xinfeng, Xunwu and Anyuan were used as the test ore samples in the present study and equilibrium batch tests of ore sample leaching using various ammonium sulfate concentrations were performed. The results show that, after leaching, there is a negative exponential relationship between the ratio of the solid-phase rare earth ion concentration to the aqueous-phase rare earth ion concentration and the initial ammonium ion concentration. However, there is a linear relationship between the natural logarithm of the ratio of the solid-phase ammonium ion concentration to the aqueous-phase ammonium ion concentration and the initial ammonium ion concentration. Based on the above two functional relationships, a two-parameter model for the equilibrium ion exchange process of ion-adsorption type rare earth ores was established. Using the established model to analyze the test data the model error for the Xunwu ore sample is found to be less than 5%. The proposed model is more accurate compared with the Kerr model. The two-parameter model proposed in this study provides theoretical support for the numerical simulation of column leaching (in-situ leaching) of ion-adsorption type rare earth ores.

Impurity fluorescence self-quenching in Nd3+: Gd3BWO9 crystalline powders: Experiment and analysis

We made precision measurements of fluorescence kinetics of crystalline Gd3BWO9: Nd3+ doped powders at room temperature by the method of gated single photon counting technique in a wide range of Nd3+ concentrations. The powders were synthesized with a high temperature solid-state reaction.We managed to describe the concentration dependence of the impurity fluorescence self-quenching kinetics curves with the constant microparameters of energy migration CDD = 2.97 nm6/ms and quenching energy transfer CDA = 0.43 nm6/ms. The microparameters were found with the direct fitting of the curves to the analytical formula of microscopic theory derived specifically for concentration fluorescence self-quenching accounting energy migration over donors. The obtained ratio of the values of the microparameters z = CDA/CDD = 0.145 indicates a hopping mechanism of fluorescence self-quenching of the 4F3/2 level of the Nd3+ ion. We developed a kinetic method to determine with high accuracy the concentrations of impurity rare-earth ions in crystals at low doping level, which is significantly higher than that for energy-dispersive X-ray spectroscopy (EDS) analysis. For arbitrary systems with fluorescence self-quenching, we obtained an analytical formula that allows us to calculate the value of the activator concentration at which the fluorescence brightness is maximum. For the studied Nd3+: Gd3BWO9 powder samples, the maximum brightness is realized at xmax≈2.98 at.%, which is in good agreement with the experimental value.

Structure, luminescence and energy transfer of Eu2,3+/Tb3+ co-doped transparent glass ceramics containing α-Ca3(PO4)2 nanocrystals

Eu2,3+/Tb3+ co-doped transparent glass ceramics containing α-Ca3(PO4)2 nanocrystals were prepared through a phase-separation-controlled crystallization route. The XRD and TEM results revealed that α-Ca3(PO4)2 nanocrystals dispersed uniformly in the CaO–P2O5–SiO2–Al2O3–ZrO2 glass matrix, and grew gradually with increasing heat-treated temperature. Optical spectroscopy analysis confirmed the self-reduction of Eu3+ to Eu2+ in the Eu-doped samples, and the luminescence was tuned with increasing heat-treated temperature and doping concentration. Noticeably, Eu2+, Tb3+ and Eu3+ ions respectively behaved as the blue, green and red luminescent centers, and thus various emitting colors were easily obtained through adjusting the doping concentrations of rare earth ions. Besides, the energy transfer mechanism between Eu2+, Tb3+ and Eu3+ was discussed.

Adjustable multicolor emission from the combination of up-conversion in Tm3+/Tb3+/Yb3+ tri-doped Na5Lu9F32 single crystals

Cubic Na5Lu9F32 fluoride single crystals tri-doped with various Tm3+/Tb3+/Yb3+ concentrations were grown by an improved Bridgman method. The absorption spectra and fluorescence spectra of Tm3+/Tb3+/Yb3+ tri-doped Na5Lu9F32 single crystal were studied systematically. The colors of up-conversion (UC) luminescence could be tuned effectively by adjusting both the doing rare earth ion concentration and the excitation laser power. The chromaticity coordinate and correlated color temperature (CCT) of the emission from the combination of the above up-conversion lights vary from (0.248, 0.261) and 18250 K to (0.325, 0.400) and 5744 K as the Tm3+/Tb3+/Yb3+ doping concentration change from 0.3 mol% Tm3+/0.3 mol% Tb3+/1 mol% Yb3+ to 0.3 mol% Tm3+/0.8 mol% Tb3+/1 mol% Yb3+ excited by a 980 nm radiation. A favorable white light emission with chromaticity coordinates of (0.297, 0.322) could be obtained from Tm3+ (0.3 mol%)/Tb3+ (0.6 mol%)/Yb3+ (1 mol%) tri-doped Na5Lu9F32 single crystal. Two-photon and three-photon absorptions dominated in the conversion processes from the infrared to visual luminescence revealed with the help of the relationship between the up-conversion emission intensity and the excitation pump power. The probable mechanism in charge of the color change of UC in Tm3+/Tb3+/Yb3+ ion doped single crystal was investigated.

Tuning the defects and luminescence of ZnO:(Er, Sm) nanoflakes for application in organic wastewater treatment

A series of ZnO nanoflakes modified with rare earth ions of Er and Sm were prepared by a simple chemical solution deposition approach. It was found that the doping content of rare-earth ions was dominant for the defects in the nanoflakes and the ability of photocatalytic degradation for rhodamine B (RhB). The ZnO:(Er, Sm) nanoflakes exhibited a superior photocatalytic activity compared to undoped ZnO mainly due to the longer lifetime of photogenerated electrons-hole pairs in the process of photocatalytic reaction, and Zn0.98Sm0.01Er0.01O nanoflakes could degrade 96.5% RhB within 60 min under UV light irradiation. PL results provided a strong evidence for the existence of VO defect, which was also found to be responsive for the enhanced photocatalytic activity of ZnO:(Er, Sm) nanoflakes. And the peaks at 515 nm and 550 nm could be attributed to the transitions of $$^{2} H_{11/2} \to^{4} I_{15/2}$$ and $$^{4} S_{3/2} \to^{4} I_{15/2}$$ from Er3+ ions, indicating the realization of green luminescence.

Random laser in Nd:YBO3 nanocrystalline powders presenting luminescence concentration quenching

Enhancement of the random laser (RL) performance in crystalline nanopowders of vaterite-type orthoborate NdxY1.000-xBO3 (0.015 ≤ x ≤ 0.040) was investigated by exciting the trivalent neodymium ions (Nd3+) at 806 nm in resonance with the ground state transitions 4I9/2→ {4F5/2, 2H9/2}. RL emission at 1056 nm, due to the Nd3+ transition 4F3/2 → 4I11/2, was observed and characterized. Although luminescence concentration quenching was detected for x > 0.007, an improvement of the RL performance was demonstrated for large Nd3+ concentrations. This feature was understood considering that the RL onset time is shorter than the nonradiative relaxation time of the 4F3/2 emitting state. The experimental results are supported by numerical simulations based on coupled rate-equations for the excited ions density and the number of photons participating in the random lasing process. The present results can motivate further RL studies with large concentration of trivalent rare-earth ions in glassy, ceramics, and crystalline matrices, which are normally avoided due to the concentration quenching.

Tunable colors and applications of Dy3+/Eu3+ co‐doped CaO‐B2O3‐SiO2 glasses

AbstractA series of Dy3+/Eu3+ single‐ and co‐doped calcium borosilicate luminescent glasses were prepared by the conventional high temperature melt‐quenching method. A compact glass structure is obtained by the addition of Dy3+/Eu3+ ions, which is verified by the physical properties of synthetic glasses. As network modifiers, Dy3+/Eu3+ fill in the interspaces of glass network and contribute to the conversion of [BO3] to [BO4]. Dy3+/Eu3+ co‐doped calcium borosilicate glasses can emit white light, which consists of blue, yellow, and red light under 387 nm excitation. The emission spectra and decay curves of the white‐emitting glasses have proved the existence of energy transfer. The average lifetime of Dy3+ decreases from 0.251 to 0.165 ms with the increasing Eu3+ concentration. Changing rare earth ions concentration, CIE color coordinates of Dy3+/Eu3+ co‐doped glass shifts from cyan to white with increasing excitation wavelength. A white‐light emission is obtained when the concentration of Dy3+ and Eu3+ equals to 4% and 2%, respectively. Moreover, the Dy3+/Eu3+ co‐doped calcium borosilicate glass shows high‐thermal stability and it may be applicable for high‐quality white LEDs based on high power near ultraviolet (n‐UV) LED chip in the future.

Influence of the rare earth ions concentration on luminescence properties of barium gallo-germanate glasses for white lighting

Barium gallo-germanate glasses co-doped with Ce3+ and Dy3+ were synthesized and their luminescence properties were studied using optical spectroscopy. The characteristic luminescence bands originating to electronic transitions of Ce3+ and Dy3+ ions were observed under direct excitation of Ce3+. Furthermore, the influence of rare earth ions concentration on luminescence properties of glass systems was examined. Luminescence lifetimes for the upper 4F9/2 excited state of Dy3+ ions were also evaluated and discussed in detail. The obtained experimental results indicate that energy transfer between these rare earth ions is possible. From the emission spectra, the Commission Internationale de I'Eclairage (CIE) chromaticity coordinates (x, y) are calculated in relation to potential application of germanate glass systems for white light emitting devices. It has been proved that our glass systems exhibit neutral/cool white emission originating from the simultaneous generation of several bands of Ce3+ and Dy3+ under the UV–visible light excitation.

Transparent Sol-Gel Oxyfluoride Glass-Ceramics with High Crystalline Fraction and Study of RE Incorporation.

Transparent oxyfluoride glass-ceramic films and self-supported layers with composition 80SiO2-20LaF3 doped with Er3+ have been successfully synthesized by sol-gel process for the first time. Crack-free films and self-supported layer with a maximum thickness up to 1.4 µm were obtained after heat treatment at the low temperature of 550 °C for 1 min, resulting in a LaF3 crystal fraction of 18 wt%, as confirmed by quantitative Rietveld refinement. This is the highest value reported up to now for transparent oxyfluoride glass-ceramics prepared by sol-gel. This work provides a new synthesis strategy and opens the way to a wide range of potential applications of oxyfluoride glass-ceramics. The characterization by a wide range of techniques revealed the homogeneous precipitation of LaF3 nanocrystals into the glass matrix. X-ray absorption spectroscopy and electron paramagnetic resonance confirmed that the Er3+ ions are preferentially embedded in the low phonon-energy LaF3 nanocrystals. Moreover, photoluminescence (PL) measurements confirmed the incorporation of dopants in the LaF3 nanocrystals. The effective concentration of rare-earth ions in the LaF3 nanocrystals is also estimated by X-ray absorption spectroscopy.

Influence of Er3+ ions on the physical, structural, optical, and thermal properties of ZnO–Li2O–P2O5 glasses

Er3+ doped zinc lithium phosphate glass samples were synthesized by the very simple melt quenching method. The obtained X-ray diffraction patterns specify that the prepared glass samples exhibit glassy nature. The physical properties like packing density, molar volume, density, oxygen packing density, interionic distance, field strength, rare earth ion concentration, and polaron radius were calculated using appropriate formulae. DTA curve was analysed to evaluate the crystallization temperature, melting temperature, and glass transition temperature and hence study the thermal properties. Fourier transform infrared spectrum was recorded to examine the functional groups in the glass and study the structural characteristics of the glass. It showed the presence of symmetrical and asymmetrical stretching vibration modes of P–O–P linkages, bending modes of P–O in PO4, bending and stretching vibrations of OH groups and P–O–H water absorbance in the glasses. The absorption spectra of the prepared glasses in the UV–visible region (wavelength 200–1100 nm) were taken to study the optical properties of the glasses. The urbach energy and optical energy bandgap values are determined using Davis–Mott method. The refractive index of all the prepared glass samples is also measured and these values are used to determine the corresponding molar refraction, the molecular polarizability of oxide ions, dielectric constant, reflection loss, metallization criterion, electronic polarizability of the oxide ions, interaction parameter, electronegativity, optical basicity, and electric susceptibility of all the glass samples using appropriate formulae.

Optical activity induced by rare-earth ions in As2S3 glasses and KCl crystals

Optical transmission spectra of As2S3 glass-like plates and nanolayers, undoped and doped with Sm and Pr ions have been investigated. The spectral dependences of the refractive index and glass transmission spectra, registered in the configuration of crossed polarizers, were studied. The concentration of rare-earth ions in the matrix influences on the magnitude of refractive indices (n−, n+) of polarized light. The emission spectra of As2S3 glasses, doped with rare-earth ions (Sm and Pr) and KCl crystals doped by Sm ions have been investigated for different temperatures in the range 300–10 K. A broad luminescence band associated with recombination transitions of charge carriers from 5D0 levels to 7F0-6 levels or from 4G5/2 levels to 6H5/2…15/2 levels of samarium ions (Sm2+ and Sm3+, respectively) was registered. A number of narrow absorption bands were registered on this broad photoluminescence band, which can be attributed to self-absorption process, determined by electronic transitions between the levels (7F0-6 ⟶ 5D0 or 6H5/2…15/2 ⟶ 4G5/2) of samarium ions.

Characterization and multicolor upconversion emission properties of BaMoO4: Yb3+, Ln3+ (Ln = Tm, Ho, Tm/Ho) microcrystals

Hydrothermal process was employed to synthesize the Yb3+/Tm3+, Yb3+/Ho3+ and Yb3+/Tm3+/Ho3+ doped BaMoO4 octahedron microcrystals (0.50–5.0 µm). The synthesized phosphors have scheelite tetragonal structure. The elemental mapping suggests the uniform distribution of elements in the samples. The oxidation state of samples were investigated by X-ray photoelectron spectroscopy (XPS) which indicates the existence of Ba2+, Mo6+, O, Yb3+, Tm3+ and Ho3+ in samples. The presence of rare earth ions was also verified by observation of specific absorption peaks in diffuse reflectance spectra (DRS). The tunable multicolor upconversion (UC) emissions were successfully obtained under 980 nm NIR excitation by precisely adjusting the concentration of rare earth ions. The as prepared sample exhibits blue, green and red emission as a result of energy transfer from the Yb3+ to Tm3+ and Ho3+ ions. The power dependent UC emission spectra show the two photonic processes. The energy transfer mechanism from Yb3+ to Tm3+ and Ho3+ was explained via an energy level analysis.

Heavily Tb3+ doped multi-component phosphate glass fibers for green fiber lasers

Heavy rare earth (RE) ion doped glass fibers make it possible to obtain high gain and high output power per unit length. It is known that high concentration of RE ions can be incorporated into multi-component phosphate glasses, which are usually used to fabricate high performance gain fibers. However, the increasing doping concentration of RE ions is mainly limited by the concentration quenching effect and crystallization during the fiber drawing process by the conventional rod-in-tube technique. In this work, no fluorescence quenching was observed in the prepared multi-component phosphate glasses even when Tb3+ doping concentration reached 16 mol %. Then, heavily Tb3+ doped multi-component phosphate glass fibers with silicate glass cladding were successfully drawn by a molten core method, which can effectively solve the crystallization problem caused by heavily RE ions doping. To the best of our knowledge, 16 mol % is the record high Tb3+ ion in phosphate glass fibers for green laser. An intense 540 nm green emission with fluorescence lifetime as long as 1.85 ms was obtained from the as-drawn fibers, showing promising applications for green fiber lasers.

Carbon quantum dot-sensitized and tunable luminescence of Ca19Mg2(PO4)14:Ln3+ (Ln3+ = Eu3+ and/or Tb3+) nanocrystalline phosphors with abundant colors via a sol–gel process

Efficient carbon quantum dot-sensitized luminescence of Ca19Mg2(PO4)14:Ln3+ (Ln3+ = Eu3+ and/or Tb3+) nanocrystalline phosphors with abundant colors.

Self-template construction of honeycomb-like mesoporous YPO4:Ln3+ (Ln = Eu, Tb) phosphors with tuneable luminescent properties

Rare earth (RE)-based phosphors with mesoporous structure that can improve the absorption and utilization of light have attracted much attention recently. Herein, we develop a novel and facile self-template strategy to synthesize honeycomb-like mesoporous YPO4:Ln3+ (Ln = Eu, Tb) phosphors using Y4O(OH)9NO3: Ln3+ as the precursor through a simple H3PO4 etching process. The maximum specific surface area of the mesoporous YPO4:Ln3+ phosphors can reach 406 m2 g−1. The influence of mesoporous structure, crystallinity, and the concentration of rare earth ions on the photoluminescence performance of mesoporous YPO4:Ln3+ phosphors was investigated. The results of fluorescence measurements indicate the mesoporous YPO4:Ln3+ phosphors exhibit better photoluminescence performance after calcination at 900 °C due to the large surface area and high crystallinity. The optimum doped concentrations of Eu3+ ions and Tb3+ ions are 0.12 and 0.08, respectively, and the concentration quenching occurs among nearest-neighbor ions. This work provide a new sight on preparation of phosphors for white light-emitting diodes lamps.

Influence of the Tb3+ concentration on the luminescent properties of high silica glass

Tb3+- doped high silica glass was prepared by sintering porous glass. The density, valence state and amount of Tb, transmittance, photoexcitation spectra, photoluminescence spectra, and cathodoluminescence spectra (CL) were recorded and the luminescence decay kinetics analyzed in details. These results show that the doping concentration in high silica glass is in direct proportion to the concentration in solution, and the density increases with the increasing concentration of rare earth ions as well as the intensity of emission spectrum. The largest emission intensity of 0.2 mol/L is more than 2 times higher than the intensity of the 0.05 mol/L. Besides, the “red” shift phenomenon could be distinguished clearly in the transmittance spectra. There is a broad band at the “red” region in the CL spectra. The decay time which is in the millisecond range in different spectral range were measured and analyzed revealing that the decay time of 5D3 is shorter than that of 5D4.

Insights Into the Sunlight-Driven Water Oxidation by Ce and Er-Doped ZrO 2.

In the present work, the activity of Ce and Er-doped ZrO2 nanopowders for sun-driven photocatalytic water oxidation has been investigated. ZrO2 powders with tunable amounts of tetragonal, monoclinic and cubic polymorphs have been synthesized by introducing Ce and Er (from 0.5 to 10 mol % on an oxide basis) through hydrothermal method. The aim of this work is to investigate the role of rare earth (RE) ions rich of electrons (Er3+) and with entirely empty levels (Ce4+) in the ZrO2 matrix for the sun-driven photocatalytic water oxidation reaction. The samples have been characterized by means of UV-Vis spectroscopy, X-Ray diffraction (XRD), N2 adsorption, X-ray photoelectron spectrophotometry (XPS) and transmission electronic microscopy (TEM) with energy dispersive spectroscopy (EDS). With respect to the bare ZrO2 mainly containing monoclinic (m-) phase, an increasing amount of rare-earth (RE) dopant was found to improve the specific BET surface area and to stabilize the tetragonal (t-) or cubic (c-) polymorphs of ZrO2 at room temperature. XRD data confirmed that dopants were mainly inserted in the t-ZrO2 phase. The photocatalytic O2 evolution from water under AM 1.5 G simulated sunlight illumination of the prepared samples have been correlated with their optical, structural and chemical properties. The effect of the dopant concentration on the chemical-physical and photocatalytic properties of the Er- and Ce-doped ZrO2 materials was elucidated. The samples with 5% of RE oxide were the most active, i.e., three times more than pure zirconia. Their superior photocatalytic activity was found to be mainly correlated to two factors: (i) an optimal surface concentration of RE ions of about 3.7%, which increased charge carriers separation in the photocatalysts surface due more superficial defects of the t-ZrO2 and a higher surface area, thus enhancing the reaction kinetics, (ii) a controlled amount of monoclinic vs. tetragonal (or cubic) polymorphs of zirconia with an optimum ratio of about 70/30 of t-ZrO2/m-ZrO2. Instead, the increased ability of the RE-doped ZrO2 to harvest visible light was found to have a secondary role on the photocatalytic activity of the Ce-doped ZrO2 material.