Lanthanide Halides Research Articles

Homoleptic organolanthanide compounds supported by the bis(dimethylsilyl)benzyl ligand.

A β-SiH functionalized benzyl anion [C(SiHMe2)2Ph]- is obtained by deprotonation of HC(SiHMe2)2Ph with KCH2Ph or by reaction of KOtBu and (Me2HSi)3CPh; LnI3(THF)n and three equivalents of this carbanion combine to provide homoleptic tris(alkyl)lanthanide compounds Ln{C(SiHMe2)2Ph}3 (Ln = La, Ce, Pr, Nd) containing secondary metal-ligand interactions.

Unprecedented magnetic behaviour in lanthanide-based ionic liquids.

Ionic liquids containing lanthanide halide anions give the opportunity to investigate magnetic behaviour in non-ordered systems. Reported herein is the synthesis and characterization of ionic liquids containing a series of lanthanide halide anions, with the resulting materials displaying unusual behaviour below 50 K. Specifically, the ionic liquid structural glass formation appears to drive magnetic behaviour due to cluster formation of the anions during rapid cooling. This system presents a possible probe to study the dynamics of glass forming materials.

Medical imaging scintillators from glass-ceramics using mixed rare-earth halides

Recent years have seen greater interest in developing new luminescent materials to replace scintillator panels currently used in medical X-ray imaging systems. The primary areas targeted for improvement are cost and image resolution. Cost reduction is somewhat straightforward in that less expensive raw materials and processing methods will yield a less expensive product. The path to improving image resolution is more complex because it depends on several properties of the scintillator material including density, transparency, and composition, among others. The present study focused on improving image resolution using composite materials, known as glass-ceramics that contain nanoscale scintillating crystallites formed within a transparent host glass matrix. The small size of the particles and in-situ precipitation from the host glass are key to maintaining transparency of the composite scintillator, which ensures that a majority of the light produced from absorbed X-rays can actually be used to create an image of the patient. Because light output is the dominating property that determines the image resolution achievable with a given scintillator, it was used as the primary metric to evaluate performance of the glass-ceramics relative to current scintillators. Several glass compositions were formulated and then heat treated in a step known as “ceramization” to grow the scintillating nanocrystals, whose light output was measured in response to a 65 kV X-ray source. Performance was found to depend heavily on the thermal history of the glass and glass-ceramic, and so additional studies are required to more precisely determine optimal process temperatures. Of the compositions investigated, an alumino-borosilicate host glass containing 56mol% scintillating rare-earth halides (BaF2, GdF3, GdBr3, TbF3) produced the highest recorded light output at nearly 80% of the value recorded using a commercially-available GOS:Tb panel as a reference.

Recent advances in rare earth scintillation crystals

Rare earth scintillation crystals act as an important media of radiation detection that could convert high-energy rays or high-energy particles to ultraviolet/visible fluorescence pulse. From the perspective of the periodic table, the rare earth scintillation crystals can be divided into rare earth halide and rare earth oxide compounds. In this review, we summarize the basic scintillation properties and crystallographic structure characteristics of some typical rare earth scintillation crystals. Rare earth ions exhibit excellent luminescent properties due to their unique 4 f electronic structure. Among the lanthanide ions, Ce3+, Pr3+, Eu2+ are chosen as efficient activator ions since they usually show spin- and parity-allowed 5 d ® 4 f transitions. The 4 f orbits of rare earth ions are shielded by filled 5 s and 5 p shells, while 5 d orbits are strongly affected by the surrounding without any shielding effect. The scintillation properties are therefore determined by the composition and structure of rare earth scintillation crystals. On the other hand, some rare earth ions, such as Y3+, La3+and Lu3+, are optically inactive, which can be regard as the ideal chemical compositions of matrix materials. An insight into the rare earth scintillation crystals is provided from the view of composition design and bulk crystal growth. We also discuss the patent protection of rare earth scintillation crystals in China. Future prospects of rare earth scintillation crystals have been briefly mentioned.

White light emission and temperature dependent chromaticity shifts by modification of luminescent ZrO(FMN) nanoparticles with rare earth halides

White light emission of composite suspensions is achieved by functionalization of ZrO(FMN) nanoparticles with lanthanide chlorides resulting in core–shell systems and a temperature dependent chromaticity shift.

Synthesis, Structural Characterization, and Chiroptical Studies of Bidentate Salen-Type Lanthanide (III) Complexes.

The salen-type ligand prepared with (R,R) diphenylethan-1,2-diamine and salicylaldehyde provides stable and inert complexes KLnL2 upon simple reaction with lanthanide halides or pseudohalides LnX3 (Ln = Tb(3+) -Lu(3+) ; X = Cl(-) or TfO(-) ) of its potassium salt. All the complexes were completely characterized through nuclear magnetic resonance (NMR), electronic circular dichroism (ECD) in the UV and some (Er(3+) , Tm(3+) , Yb(3+) ) also with Near-IR ECD (NIR-ECD) and luminescence (Tb(3+) , Tm(3+) ). Careful analysis of the NMR shifts demonstrated that the complexes are isostructural in solution and afforded an accurate geometry. This was further confirmed by means of Density Functional Theory (DFT) optimization of the Lu(3+) complex, and by comparing the ligand-centered experimental and time-dependent TD-DFT computed UV-ECD spectra. As final validation, we used the NIR-ECD spectrum of the Yb(3+) derivative calculated by means of Richardson's equations. The excellent match between calculated and experimental ECD spectra confirm the quality of the NMR structure.

Impact of low-energy photons on the characteristics of prompt fissionγ-ray spectra

In this paper we report on a new study of prompt $\ensuremath{\gamma}$-rays from the spontaneous fission of ${}^{252}\mathrm{Cf}$. Photons were measured in coincidence with fission fragments by employing four different lanthanide halide scintillation detectors. Together with results from a previous work of ours, we determined characteristic parameters with high precision, such as the average $\ensuremath{\gamma}$-ray multiplicity ${\overline{\ensuremath{\nu}}}_{\ensuremath{\gamma}}\phantom{\rule{0.16em}{0ex}}=(8.29\phantom{\rule{0.16em}{0ex}}\ifmmode\pm\else\textpm\fi{}\phantom{\rule{0.16em}{0ex}}0.13)$, the average energy per photon ${\ensuremath{\epsilon}}_{\ensuremath{\gamma}}\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}(0.80\phantom{\rule{0.16em}{0ex}}\ifmmode\pm\else\textpm\fi{}\phantom{\rule{0.16em}{0ex}}0.02)$ MeV, and the total $\ensuremath{\gamma}$-ray energy release per fission ${E}_{\ensuremath{\gamma},\text{tot}}\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}(6.65\phantom{\rule{0.16em}{0ex}}\ifmmode\pm\else\textpm\fi{}\phantom{\rule{0.16em}{0ex}}0.10)$ MeV. The excellent agreement between the individual results obtained in all six measurements proves the good repeatability of the applied experimental technique. The impact of low-energy photons, i.e., below 500 keV, on prompt fission $\ensuremath{\gamma}$-ray spectra characteristics has been investigated as well by comparing our results with those taken with the DANCE detector system, which appears to suffer from absorption effects in the low-energy region. Correction factors for this effect were estimated, giving results comparable to ours as well as to historical ones. From this we demonstrate that the different techniques of determining the average $\ensuremath{\gamma}$-ray multiplicity, either from a properly measured and normalized spectrum or a measured multiplicity distribution, give equivalent and consistent results.

Electrical conductivity of molten cesium chloride–dysprosium(III) chloride system

Electrical conductivity of the molten binary CsCl–DyCl3 system has been measured in the temperature range of 898–1233K. There were given equations of temperature dependences of specific and molar conductivities of melts for 0≤xDyCl3≤1. Dependence of the CsCl–DyCl3 system conductivity on the melt composition was compared with sodium and potassium analogues as well as CsCl–light lanthanide ones (La–Pr). It was found that the minimum of molar conductivity in the CsCl–DyCl3 system is at typical composition of the melt (xDyCl3=0.40–0.50) but further increase of the melt conductivity is apparently weaker. The results have been briefly commented in terms of literature findings on the lanthanide halides–alkali metal halide system structure.

Persistence Mechanisms and Applications of Long Afterglow Phosphors

This article presents a broad review of long persistence (LP) materials that are a special kind of photon energy storage and conversion materials. They are also known as long afterglow phosphors or long decay phosphors (LDP). These phosphors can be readily excited by any ordinary household lamp, sunlight and/or ambient room lights and glow continuously in the dark for hours together without involving any radioactive elements. It is the modifications that are made to crystalline host lattice that exhibit these unusual properties related to persistence due to effective doping of some transition or rare-earth ions. A slight variation in the processing parameters such as type of reducing atmosphere, stoichiometric excess of one or more constituents, the nature of fluxes, and the intentional addition of carbon or rare-earth halides can drastically shift the emission colors and persistence times of the LP phosphors in the visible spectrum. Historically, Cu-doped ZnS phosphor had been a traditional LP material with its afterglow time less than an hour. The emission color of these LP phosphors was confined between green and yellow-green region only. However, synthesis of blue and red-emitting phosphors with long persistence times had been always a challenging task. This review article covers the recent advances in the blue, green and red-emitting LP phosphors/nanophosphors, persistence mechanism involved and the basic problems associated with their luminescence efficiency and persistence times. Modifications to existing nanosynthesis protocols to formulate a nontoxic Green Chemistry Route are also presented.Contents of Paper1. Long Afterglow Phosphors

In situ synthesis of lanthanide complexes supported by a ferrocene diamide ligand: extension to redox-active lanthanide ions

The scope of an in situ method to prepare rare-earth alkyl and halide precursors was extended to cerium, praseodymium, samarium, terbium, thulium, and ytterbium.

Does the 4f-shell contribute to bonding in tetravalent lanthanide halides?

Lanthanide tetrahalide molecules LnX4 (Ln = Ce, Pr, Tb; X = F, Cl, Br, I) have been investigated by density functional theory at the levels of the relativistic Zero Order Regular Approximation and the relativistic energy-consistent pseudopotentials, using frozen small- and medium-cores. The calculated bond lengths and vibrational frequencies are close to the experimental data. Our calculations indicate 4f shell contributions to bonding in LnX4, in particular for the early lanthanides, which show significant overlap between the Ln 4f-shell and the halogen np-shells. The 4f shells contribute to Ln-X bonding in LnX4 about one third more than in LnX3.

Gold nanoparticles and their alternatives for radiation therapy enhancement.

Radiation therapy is one of the most commonly used treatments for cancer. The dose of delivered ionizing radiation can be amplified by the presence of high-Z materials via an enhancement of the photoelectric effect; the most widely studied material is gold (atomic number 79). However, a large amount is needed to obtain a significant dose enhancement, presenting a challenge for delivery. In order to make this technique of broader applicability, the gold must be targeted, or alternative formulations developed that do not rely solely on the photoelectric effect. One possible approach is to excite scintillating nanoparticles with ionizing radiation, and then exploit energy transfer between these particles and attached dyes in a manner analogous to photodynamic therapy (PDT). Doped rare-earth halides and semiconductor quantum dots have been investigated for this purpose. However, although the spectrum of emitted light after radiation excitation is usually similar to that seen with light excitation, the yield is not. Measurement of scintillation yields is challenging, and in many cases has been done only for bulk materials, with little understanding of how the principles translate to the nanoscale. Another alternative is to use local heating using gold or iron, followed by application of ionizing radiation. Hyperthermia pre-sensitizes the tumors, leading to an improved response. Another approach is to use chemotherapeutic drugs that can radiosensitize tumors. Drugs may be attached to high-Z nanoparticles or encapsulated. This article discusses each of these techniques, giving an overview of the current state of nanoparticle-assisted radiation therapy and future directions.

Application of the quasi-random lattice model to rare-earth halide solutions for the computation of their osmotic and mean activity coefficients

This work dealt with the computation of the mean activity coefficients of rare-earth halide aqueous solutions at 25°C, by means of the Quasi Random Lattice (QRL) model. The osmotic coefficients were then calculated consistently, through the integration of the Gibbs-Duhem equation. Using of QRL was mainly motivated by its dependence on one parameter, given in the form of an electrolyte-dependent concentration, which was also the highest concentration at which the model could be applied. For all the electrolyte solutions here considered, this parameter was experimentally known and ranged from 1.5 to 2.2 mol/kg, at 25 °C. Accordingly, rare-earth halide concentrations from strong dilution up to 2 mol/kg about could be considered without need for best-fit treatment in order to compute their osmotic and mean activity coefficients. The experimental knowledge about the parameter was an advantageous feature of QRL compared to existing literature models. Following a trend already observed with low charge electrolytes, a satisfactory agreement was obtained with the experimental values for all the investigated rare-earth chlorides and bromides. For the sake of compactness, in this work the considered rare-earth halides were all belonging to the P63/m space group in their crystalline (anhydrous) form.

Can a simple ionic model provide useful enthalpies of formation values?

A simple ionic model is revisited. The model starts with the calculation of lattice energy and thus the thermochemical radii of the ions. These radii allow the calculation of other lattice energies and through a Born–Haber cycle to obtain the enthalpy of formation. By using literature available for experimental data, the model was tested to see if it can provide reliable enthalpies of formation values. As presented in this contribution, the method only applies to binary compounds with both simple and complex ions. As examples of the usefulness of this approach, enthalpies of formation of unmeasured crystalline ionic liquids (Hmim+, C2mim+, C4mim+ and NH4+ families) and lanthanide (II) halides were determined. The latter ones were used to address the stability of lanthanide halides in states II and III.

Influence of Ce doping concentration on the luminescence properties of LaCl3：Ce scintillation crystals

LaCl3:Ce is an excellent rare earth halide scintillation crystal discovered in the beginning of this century. Pure LaCl3 crystal and LaCl3 crystal doped with several different Ce concentrations were grown by vertical Bridgman method. Their transmission and luminescence as well as decay time were measured and compared with each other. It was found that the cut-off edge, emission wavelength as well as decay time for pure LaCl3 crystals are respectively 215 nm, 405 nm and 1 s. This emission is explained by the self trapped exciton (STE) of LaCl3. However, with the increase of Ce concentration in the crystal, the cut-off edge of LaCl3:Ce crystal shifts to about 300 nm, and the luminescence is dominated by the emission originating from 5d-4f transition of Ce ions. Meanwhile, the increase of the luminescence intensity of Ce3+ ion emission is accompanied with the expense of STE emission, this anti-correlation between the Ce3+ and STE luminescence intensity is interpreted by the energy transfer from STE to Ce ions in LaCl3:Ce scintillation crystals.

Synthesis and luminescence properties of transparent nanocrystalline GdF3:Tb glass-ceramic scintillator

Transparent glass-ceramic containing rare-earth doped halide nanocrystals exhibits enhanced luminescence performance. In this study, a glass-ceramic with Tb doped gadolinium fluoride nanocrystals embedded in an aluminosilicate glass matrix is investigated for X-ray imaging applications. The nanocrystalline glass-ceramic scintillator was prepared by a melt-quench method followed by an anneal. The GdF3:Tb nanocrystals precipitated within the oxide glass matrix during the processing and their luminescence and scintillation properties were investigated. In this nanocomposite scintillator system, the incorporation of high atomic number Gd compound into the glass matrix increases the X-ray stopping power of the glass scintillator, and effective energy transfer between Gd3+ and Tb3+ ions in the nanocrystals enhances the scintillation efficiency.

Effect of host glass matrix on structural and optical behavior of glass–ceramic nanocomposite scintillators

Composite scintillator systems have received increased attention in recent years due to their promise for merging the radioisotope discrimination capabilities of single crystal scintillators with the high throughput scanning capabilities of portal monitors. However, producing the high light yield required for good energy resolution has proven challenging as scintillation photons are often scattered by variations in refractive index and agglomerated scintillator crystals within the composite. This investigation sought to mitigate these common problems by using glass–ceramic nanocomposite materials systems in which nanoscale scintillating crystallites are precipitated in a controlled manner from a transparent glass matrix. Precipitating crystallites in situ precludes nanoparticle agglomeration, and limiting crystallite size to 50nm or less mitigates the effect of refractive index mismatch between the crystals and host glass. Cerium-doped gadolinium bromide (GdBr3(Ce)) scintillating crystals were incorporated into sodium-aluminosilicate (NAS) and alumino-borosilicate (ABS) host glass matrices, and the resulting glass–ceramic structures and luminescence behavior were characterized. The as-cast glass from the ABS system displayed a highly ordered microstructure that produced the highest luminescence intensity (light yield) of the samples studied. However, heat treating to form the glass–ceramic precipitated rare-earth oxide crystallites rather than rare-earth halides. This degraded light yield relative to the unaged sample.

Large-Area Crystalline Microcolumnar LaBr$_{3}$:Ce for High-Resolution Gamma Ray Imaging

Novel fabrication methods for cost-effective and large-volume production of important lanthanide halide scintillators are currently being explored. Here we report on the growth of LaBr :Ce scintillator films in a novel light conserving morphology known as Crystalline Microcolumnar StructureTM (CMSTM), using Hot Wall Evaporation (HWE) technique. This method produces specimens which preserve the response uniformity over the area of the film, and low attenuation of light throughout its thickness. Using this approach, we have produced LaBr :Ce film samples measuring 3-7 cm in diameter and approaching 2 cm in thickness, with densely packed microcolumns averaging ~15 μm in diameter. Some of these films show bright light emissions compared to their crystalline counterparts, demonstrating energy resolution of ~9.4% at 122 keV ( Co emission) and uniformity in light response across the area of the scintillator. Imaging data acquired using the University of Arizona Bazooka SPECT detector incorporating our CMS LaBr :Ce film demonstrated m spatial resolution ~138 μm at 122 keV in single-photon counting imaging mode. This technique permits fabrication of thick films that can simultaneously provide the high absorption efficiency and high spatial resolution required for small-animal SPECT imaging and other medical and non-medical applications.

New cerium-based metal–organic scintillators for radiation detection

We have previously shown that a new class of scintillating materials can be developed based on the synthesis and crystal growth of rare-earth metal–organic compounds. The first scintillator of this type consisted of single crystals of CeCl3(CH3OH)4 that were grown from a methanol solution. These crystals were shown to be applicable to both gamma-ray and fast neutron detection. Subsequently, metal–organic scintillators consisting of the compound LaBr3(CH3OH)4 activated with varying levels of Ce3+ and of CeBr3(CH3OH)4 were grown in single crystal form. We have now extended the development of this new class of scintillators to more complex organic components by reacting rare-earth halides such as CeCl3 or CeBr3 with different isomers of propanol and butanol—including 1-propanol, isobutanol, n-butanol, and tert-butanol. The reaction of CeCl3 or CeBr3 with these organics results in the formation of new and relatively complex molecular crystals whose structures were determined using single-crystal X-ray diffraction. These new metal–organic scintillating materials were grown in single crystal form from solution, and their scintillation characteristics have been investigated using X-ray-excited luminescence plus energy spectra obtained with gamma-ray and alpha-particle sources. If the reactions between the inorganic and organic components are not carried out under very dry and highly controlled conditions, molecular structures will be formed that incorporate waters of hydration. The present observation of scintillation in these hydrated rare-earth metal–organic compounds is apparently an original finding, since we are not aware of any previous reports of scintillation being observed in a material that incorporates waters of hydration.

Identifying a Structural Preference in Reduced Rare-Earth Metal Halides by Combining Experimental and Computational Techniques

The structures of two new cubic {TnLa(3)}Br(3) (Tn = Ru, Ir; I4(1)32, Z = 8; Tn = Ru: a = 12.1247(16) Å, V = 1782.4(4) Å(3); Tn = Ir: a = 12.1738(19) Å, V = 1804.2(5) Å(3)) compounds belonging to a family of reduced rare-earth metal halides were determined by single-crystal X-ray diffraction. Interestingly, the isoelectronic compound {RuLa(3)}I(3) crystallizes in the monoclinic modification of the {TnR(3)}X(3) family, while {IrLa(3)}I(3) was found to be isomorphous with cubic {PtPr(3)}I(3). Using electronic structure calculations, a pseudogap was identified at the Fermi level of {IrLa(3)}Br(3) in the new cubic structure. Additionally, the structure attempts to optimize (chemical) bonding as determined through the crystal orbital Hamilton populations (COHP) curves. The Fermi level of the isostructural {RuLa(3)}Br(3) falls below the pseudogap, yet the cubic structure is still formed. In this context, a close inspection of the distinct bond frequencies reveals the subtleness of the structure determining factors.