Distribution Of Rare Earth Ions Research Articles

Mechanical Alloying and Concentration Quenching of the Luminescence of Pr3+ Ions in Chalcogenide Glass

The disadvantage of chalcogenide glasses containing rare earth ions as luminescent materials for the IR optical range is the strong concentration quenching of luminescence due to the non-uniform distribution of rare earth ions in the glass matrix. This study investigates the effect of grinding chalcogenide glass containing Pr3+ ions in a planetary ball mill on its luminescent properties in the near-IR range, as well as its optical properties and structure. The results indicate that milling, under certain conditions, leads to a decrease in the concentration quenching of the luminescence of Pr3+ ions. This finding suggests that milling can be used in the development of glassy materials with the increased efficiency of luminescence of rare earth ions. However, it is essential to consider that high-energy milling may result in the formation of areas with increased pressure in the obtained material, leading to structural changes in the glass.

Green Synthesis of Deep Ultraviolet Response Nanophosphors with Tunable Full-visible-spectra Emission for Luminescent Temperature Sensing

Background: Recently, the CaMoO4 nanocrystal has been viewed as one of the most promising substrates for rare-earth-doped nanophosphors due to its high density, stable chemical properties, and good deep-ultraviolet (DUV) responding characteristics. Aim: In this work, a green synthesis approach is proposed to obtain rare-earth-doped CaMoO4 nanodispersion with full-visible-spectra emission by using an ethanol-water mixed solvent in a rotating packed bed (RPB) reactor. Method: The obtained nanophosphors exhibited bright luminescent emission with tunable color in the range of full-visible-spectra via doping of Eu3+, Tb3+, and Dy3+, when they were excited by deepultraviolet (DUV) light. The RPB promoted the uniform distribution of rare-earth ions and the crystallinity of CaMoO4 particles, and the use of ethanol-water as solvents with no toxicity and less environmental pollution was beneficial for large-scale production. Result: The quantum yields for nanophosphors of CaMoO4: Na+, Eu3+, CaMoO4: Na+, Tb3+, and Ca- MoO4: Na+, Dy3+ were measured to be 46.96 %, 28.05 %, and 10.27 %, respectively, which were among the highest values ever reported for rare-earth-doped CaMoO4-based nanophosphors with similar morphology. The temperature-dependent luminescence of CaMoO4: Eu3+, Na+ nanophosphors was investigated in the range of 298 K - 498 K. Conclusion: The clear correlation between luminescence intensity and temperature indicates the potential novel application areas for CaMoO4: Na+, Eu3+ nanophosphor as a non-invasive thermometer. Upon regulating different nanophosphor material ratios, the obtained product shows a flexible fluorescence towards full-visible-spectra emission.

Influence of Boron anomaly on the NIR fluorescence concentration quenching of erbium ions in borate glasses

Constructing the glass matrix to avoid the concentration quenching is significant to obtain heavily doping and higher optical gain glasses. In this work, B2O3-Na2O binary glasses with different O/B were employed for discussing the relationship between the glass structure and erbium ions concentration quenching. The Raman spectra indicated that when the O/B was 0.16, the [BO3] would be mostly transformed into [BO4] in the glass network, and furtherly increased O/B, the [BO3] would not be transformed into [BO4] continuously. The critical doping concentration was highest when the O/B was 0.16, which suggested that the relative complete framework structure would be beneficial to obtain homogenously distribution of rare earth ions. Lower O/B, more diverse of the glass structure units, which would be favor to obtain broadband width of NIR fluorescence of Er3+ ions.

Enhanced up-conversion red light emission from rare earth titanium oxide nanocrystals with pyrochlore phase

A facile sol-gel method combined with the post-annealing process has been used to synthesize Yb3+/Er3+ co-doped TiO2 nanocrystals. It is found that the high Yb3+ concentrations can promote the formation of TiO2 nanocrystals with pyrochlore phase. An intense up-conversion (UC) red light emission (658 nm) has been achieved under 980 nm laser excitation, which is enhanced by 108 folds compared with the reference sample. Both the luminescence intensity and the red-to-green emission intensity ratio are dependent of the annealing temperature, which can be explained as the distribution of rare-earth ions and phase change of TiO2 nanocrystals.

Blue to NIR down-conversion in Tm3+/Yb3+-codoped fluorozirconate glasses compared to Pr3+/Yb3+ ion-pair

Visible to near infrared down-conversion has been studied in Tm3+/Yb3+-codoped fluorozirconate glasses, namely ZBLA (57ZrF4-34BaF2-5LaF3-4AlF3 in mol%) and ZLAG (70.2ZrF4-23.4LaF3−0.6AlF3-5.8GaF3 in mol%). Upon blue excitation at 467nm, Tm3+ doped glasses yield weak red at 650nm and strong luminescence around 800nm. With the addition of Yb3+, emission between 950 and 1100nm from the Yb3+: 2F5/2 → 2F7/2 transition was observed. This emission well matched with the band gap of crystalline silicium. The mechanism responsible for down-conversion in the Tm3+/Yb3+ ion-pair is a down-shifting process. The highest energy transfer efficiency ηETE was 64.5% in ZBLA glasses doped with 0.75Tm3+/10Yb3+; this efficiency was mainly limited by the strong Yb3+ to Tm3+ back energy transfer. ηETE appeared to increase more rapidly with the addition of Yb3+ in ZLAG glasses, as already observed for the energy transfer in Pr3+/Yb3+ ion-pair. The origin of the difference between the two hosts is probably related to the distribution of rare-earth ions in the host matrix, as shown by molecular dynamics simulation.The Tm3+/Yb3+ system is found much less efficient that the Pr3+/Yb3+ one, because of less efficient quantum efficiency together with lower blue absorption of Tm3+ compared to Pr3+.

Upconversion luminescence of a transparent glass ceramics with hexagonal Na(Gd,Lu)F4 nanocrystals

Novel Er3+ doped transparent glass ceramics containing hexagonal Na(Gd,Lu)F4 nanocrystals were prepared from oxyfluoride glasses. The distribution of rare earth ions in the crystalline and glassy phase has been analyzed by X-ray diffraction and erbium luminescence decay kinetics measurement. A strong deviation of rare earth ion content in fluoride nanocrystals in comparison to the base glass has been observed. Preferential incorporation of Gd3+ over Lu3+ ions in the fluoride lattice leads to the stabilization of hexagonal Na(Gd,Lu)F4 structure and prevents the formation of cubic fluorite type solid solutions. A considerable enhancement of upconversion luminescence correlates with the formation of hexagonal solid solutions and is attributed to an efficient energy transfer between Er3+ ions.

Luminescent DNA- and agar-based membranes.

Luminescent materials containing europium ions are investigated for different optical applications. They can be obtained using bio-macromolecules, which are promising alternatives to synthetic polymers based on the decreasing oil resources. This paper describes studies of the DNA- and Agar-europium triflate luminescent membranes and its potential technological applications are expanded to electroluminescent devices. Polarized optical microscopy demonstrated that the samples are birefringent with submicrometer anisotropy. The X-ray diffraction analysis revealed predominantly amorphous nature of the samples and the atomic force microscopy images showed a roughness of the membranes of 409.0 and 136.1 nm for the samples of DNA10Eu and Agar1.11Eu, respectively. The electron paramagnetic resonance spectra of the DNA(n)Eu membranes with the principal lines at g ≈ 2.0 and g ≈ 4.8 confirmed uniform distribution of rare earth ions in a disordered matrix. Moreover, these strong and narrow resonance lines for the samples of DNA(n)Eu when compared to the Agar(n)Eu suggested a presence of paramagnetic radicals arising from the DNA matrix. The emission spectra suggested that the Eu3+ ions occupy a single local environment in both matrices and the excitation spectra monitored around the Eu emission lines pointed out that the Eu3+ ions in the Agar host were mainly excited via the broad band component rather than by direct intra-4f(6) excitation, whereas the opposite case occurred for the DNA-based sample.

Short- and medium-range structures of cerium aluminophosphate glasses: A molecular dynamics study

Properties of rare earth aluminophosphate glasses depend profoundly on the local coordination environments and the distribution of rare earth ions, as well as the glass-forming network structures that accommodate these rare earth ions. In this paper, we have studied the structure of a series of cerium aluminophosphate glasses with both Ce3 + and Ce4 + oxidation states using larger classical molecular dynamics (MD) simulations (with over 13,000 atoms) for a wide range of cerium oxide concentrations (1.8–23.8 mol%). The simulated structure models were validated by comparing with the structure factor and correlation function from high energy X-ray diffraction studies. The short- and medium-range structure characteristics of these glasses as a function of composition have been obtained. P5 + ions are found to be fourfold coordinated and their local structure remains unchanged in the entire series while the coordination environments around Al3 +, Ce3 +, and Ce4 + ions show composition dependence. Aluminum ions are mainly four-coordinated with considerable increase of five-coordinated with increasing alumina content. Cerium distribution was analyzed by clustering analysis, [CeOx] polyhedra connectivity analyses, and Ce–Ce pair distribution functions. It was found that relatively high cerium oxide concentration (~ 14 mol%) can be incorporated in the glasses while maintaining the desired cerium ion distribution. With higher cerium content, cerium cluster formation is inevitable and characterized by increasing cluster size by the formation of direct Ce–O–Ce linkages.

Europium environment and clustering in europium doped silica and sodium silicate glasses

The local environment and distribution of rare earth ions are important to the optical properties of rare earth doped oxide glasses. In this paper, we report studies of the structures of europium doped (around 1 mol% Eu 2O 3) silica and sodium silicate glasses using molecular dynamics simulations. By using effective partial charge potentials, systems with over 24,000 atoms were modeled in order to obtain better statistics of rare earth ion distribution. The simulated glass structures were validated by comparing the calculated neutron and X-ray structure factors with experimental data. It was found that europium ions have higher coordination number (5.9 versus 4.8) and more symmetric environments in sodium silicate glasses than in the silica glass. Rare earth ion clustering has been characterized in detail and it was found that the clustering probability of europium ions in sodium silicate glass is consistently less than that predicted from a random distribution, while the probability of clustering in pure silica glass is higher than that of random distribution at the 1 mol% doping level.

Magnetic properties of Er1−xDyxAl2 (≤x≤1) compounds in low applied fields

Low field magnetic properties of the Laves phase RAl2 compounds (where R is a mixture of Er and Dy, i.e., Er1−xDyx and x=0, 0.1, 0.14, 0.18, 0.25, 0.33, 0.5, and 1) have been studied. These compounds order ferromagnetically, and the middle members show both metastability in a narrow temperature window within the ferromagnetically ordered state and signatures of first order transitions in low applied fields. Results of first principles electronic structure calculations on Er0.75Dy0.25Al2 indicate a significant difference in the spin polarization in the 5d states of Er3+ and Dy3+ moments. In addition, anisotropic exchange and crystalline electric field effects arise from the random distribution of rare earth ions in the lattice. These and quadrupolar effects triggered by aspherical charge distributions of Er3+ and Dy3+ ions may compete and lead to the low temperature anomalies observed in low field magnetization data.

EPR and vibrational studies of YVO 4:Tm 3+, Yb 3+ single crystal

A well oriented YVO 4 single crystal, with 5% Yb 3+ and 2% Tm 3+ nominal doping, was investigated using the Raman and EPR techniques. The EPR measurements suggest that Yb 3+ ions occupy eight-coordinated Y 3+ sites forming bisdisphenoids of the D 2d symmetry. An inhomogeneous distribution of rare-earth ions leads to a significant distortion of the local point symmetry ( C 1). It seems that strong dipole–dipole interactions between Yb 3+ ions are responsible for the distortion. As a result, two types of ytterbium magnetic centers appear. They correspond to paired magnetic centers and distorted isolated paramagnetic centers that are strongly sensitive to the magnetic field directions and some imperfections of the crystal. Pair centers can be recorded through the rotation around the c-crystal axis, whereas isolated centers can be measured when the crystal is rotated around the a-crystal axis. With the increasing temperature, the ytterbium signal disappeared at about 23 K and a group of narrow lines became visible. These lines, observed in the range of 240–550 mT, correspond to the Gd 3+ ( S = 7/2) ions, doped to the structure unintentionally from the basic materials.

Novel polyaryletherketones bearing pendant carboxyl groups and their rare earth complexes, Part I: Synthesis and characterization

A series of novel polyaryletherketones bearing pendant carboxyl groups were synthesized via solution nucleophilic polycondensation reaction, and the rare earth (Re3+=Sm3+, Eu3+, Dy3+ and Tb3+) coordinated polymers were prepared using the polymer as macromolecular ligand and 1,10-phenanthroline (Phen), dibenzoylmethane (DBM) or 8-hydroxyquinoline (HQ) as co-ligands. Their structures were confirmed by means of FT-IR, 1H NMR and WAXD methods. WAXD results showed that the rare earth-coordinated polymer had similar amorphous structure to the polymer matrix, whereas the diffraction peaks corresponding to rare earth salts were completely absent, indicating a homogeneous distribution of rare earth ions within the polymer hostess due to the formation of coordination bonds between rare earth ions and the carboxyl groups on the polymer backbone. The rare earth coordination polymers were soluble in polar solvents such as DMSO, DMAc, DMF and NMP, and could be easily cast into transparent tough thin films. The polyaryletherketones synthesized had high glass transition temperatures above 210°C, and showed fairly good thermal stability with 5% thermal decomposition loss above 402°C.

Rare earth ion distribution in sol–gel silicate glasses

Sol–gel glasses are porous networks that have been densified through chemical processing and heat treatment. Due to their relative insolubility in silica, rare earth (RE) ions in silicate glasses enter as network modifiers and compete for non-bridging oxygens in order to complete their coordination. Energy transfer between Tb 3+ ions is used here to study the distribution of RE ions in these porous glasses. The non-exponential decay of the 5D 3 fluorescence is due to cross relaxation. Using a model for energy transfer in fractional dimensions and fitting the decay profile to a stretched exponential, the number of nearby Tb 3+ ions and the dimensionality of the Tb 3+ ions in the pores could be determined. Analysis indicates that the observed fluorescence originates from relatively isolated ions. Samples annealed below 950 °C exhibit a dimensionality of ∼1.2.

Rare-earth ion distribution in sol–gel glasses co-doped with Al 3+

Terbium spectroscopy is used to probe clustering of rare earth (RE) ions in sol–gel glasses. We use pulsed laser experiments to study energy transfer among Tb 3+ dopants, and analyze the fluorescence decay curves using the Inokuti–Hirayama model. The analysis yields new insights about the role of Al 3+ co-doping. Assuming a multipolar interaction, we derive an effective Tb 3+ concentration for a series of samples with varying amounts of RE. When actual doping concentration is varied over 2 orders of magnitude, the effective Tb 3+ concentration of centers that emit light changes by only a factor of 10. The results indicate that Al 3+ co-doping is only effective at dispersing RE ions when the ratio of Al:RE is 10:1 or greater. At higher RE concentrations, most ions reside in clusters; 5D 3 fluorescence is observed from a minority of isolated ions. This interpretation contradicts earlier work that used fluorescence line narrowing to demonstrate that Al 3+ co-doping caused RE dispersal at high doping levels.

Spatial distribution of rare-earth ions in Se-based chalcogenide glasses with or without Ga

Measured lifetime of the ( 3F 3, 3F 4) level of Pr 3+ ions doped in representative Se-based chalcogenide Ge–Sb–Se glasses peaked at the mean coordination number of ∼2.67, indicating that inter-ionic distance between Pr 3+ dopants became maximized on the average at such particular host compositions. However, this phenomenon was not observed when Ga was further introduced. It has been verified from Ga K-edge EXAFS spectroscopic analysis that a Ga atom has four Se atoms as its nearest neighbors in the Ge–Sb–Se glasses doped with Pr. The Ga–Se bonds are less covalent than other heteropolar chemical bonds, and thereby positively ionized rare-earth elements would be located preferentially next to the GaSe 4 units, acting as charge compensators or network modifiers. We presume that there is a negligible structural and chemical correlation between a rare-earth ion and its next-nearest neighbors on their sites in the typical covalent chalcogenide glasses without Ga, and as a result spatial distribution of rare-earth ions would depend on changes of the free volume accompanied with the structural phase transitions on a medium-range scale from two-dimensional layers to three-dimensional networks. In selenide glasses with Ga, however, the empirical connection disappears due to the structural correlation between rare-earth ions and the GaSe 4 tetrahedra.

Structured diffuse scattering, local crystal chemistry and metal ion ordering in the (1 − x )MgS · x /3Yb2S3, 0 ≤ x ≤ ∼ 0.45, ‘defect’ NaCl system

Rare earth sulfide solid solutions of ‘defect’ NaCl average structure type exhibit excellent colour characteristics and thus represent good prospects for use in the paints and plastics industry. As the colour characteristics of such systems are closely related to the local distribution of rare earth ions, it is important to know as much as possible about the latter. In this contribution, the reciprocal space shape of a highly structured, diffuse intensity distribution observed in a (1 −x)MgS · xYb2/3S, x = 0.30, sample is used to show that the smallest polyhedral building blocks of the average NaCl structure type should each have, as far as possible, the same composition as the overall macroscopic composition. Local crystal chemical considerations suggest that both the Yb3+ ions and the vacancies □ would prefer to be opposite Mg2+ ions.

Direct spectroscopic observation of the atomic-scale mechanisms of clustering and homogenization of rare-earth dopant ions in vitreous silica

Structural aspects of clustering of rare earth ions in oxide glasses have been studied for the last several years in relation to their applications in photonics. However, the mechanism of homogenization of the spatial distribution of rare earth ions by codoping, typically with Al or P, is still not well understood. In this work we report direct experimental determination of the homogenization mechanism of ${\mathrm{Yb}}^{3+}$ ion clusters in silica glasses doped with $0.1\phantom{\rule{0.3em}{0ex}}\mathrm{wt}.\phantom{\rule{0.2em}{0ex}}%$ ${\mathrm{Yb}}_{2}{\mathrm{O}}_{3}$ and codoped with Al or P, using two-dimensional HYSCORE-EPR spectroscopy. The results lead us to conclude that Yb creates its coordination environment via formation of $\mathrm{Yb}\text{\ensuremath{-}}\mathrm{O}\text{\ensuremath{-}}\mathrm{Si}$ and $\mathrm{Yb}\text{\ensuremath{-}}\mathrm{O}\text{\ensuremath{-}}\mathrm{Yb}$ bonds in a Yb-doped silica glass and even the light codoping with Al starts replacing these bonds with $\mathrm{Yb}\text{\ensuremath{-}}\mathrm{O}\text{\ensuremath{-}}\mathrm{Al}$ linkages. Heavy codoping with P replaces all $\mathrm{Yb}\text{\ensuremath{-}}\mathrm{O}\text{\ensuremath{-}}\mathrm{Si}∕\mathrm{Yb}$ linkages with $\mathrm{Yb}\text{\ensuremath{-}}\mathrm{O}\text{\ensuremath{-}}\mathrm{P}$ linkages. The formation of a next-nearest neighbor shell of Al or P creates suitable structural pockets, which ultimately leads to homogenization.

Investigation on the Distribution of Rare Earth Ions in Strontium Aluminate Phosphors.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Investigation on the distribution of rare earth ions in strontium aluminate phosphors

Long afterglow pigment SrAl 2O 4:Eu,Dy was synthesized by a solid-state reaction method, the effects of flux B 2O 3 on the sintering dynamic process and the distribution of the rare earth ions Eu and Dy in strontium aluminate phosphors were investigated. It is shown that most of the rare earth ions are precipitated in the grain boundary phase, which is formed by the addition of B 2O 3 flux, therefore the amount of rare earth activator to be added is larger than the practically necessary amount. B 2O 3 promotes the growth of the SrAl 2O 4 matrix strongly as well as decreases the synthesis temperature of SrAl 2O 4 remarkably. The rare earths ions diffuse into the SrAl 2O 4 host lattice rapidly through grain boundary diffusion, therefore, the afterglow time of SrAl 2O 4:Eu,Dy can be increased from 1000 min to above 6000 min.

Improving the photoluminescence of thin films by nanostructuring the rare-earth ion distribution

Pulsed laser deposition has been used to prepare nanostructured rare-earth-doped films. Alternate deposition from the host (Al 2O 3) and dopant (Er, Yb) targets has been used to obtain artificially structured films in which the rare-earth ion–ion separation is controlled in the nanometer scale (0.5–9 nm). In the case of Er 3+–Er 3+ interactions, it has been found that self-quenching is greatly reduced for separations larger than 3 nm. The control of the laser fluence used for Er ablation is also important, and higher fluences lead to higher luminescence efficiencies. The Er and Yb co-doped films have been designed with the Er 3+ and Yb 3+ ions distributed either in the same layer or in different layers separated from 1 to 3 nm. The emission intensity in these co-doped films can be up to two orders of magnitude higher than that reported for films doped only with Er. The results evidence that structuring the rare-earth distribution in the nanometer scale is a very efficient means to reduce rare-earth clustering. Finally, it will also be shown that nanostructuring offers a valuable method to analyze ion–ion interactions such as energy transfer mechanisms.