RE Cations Research Articles

Synthesis and properties of anhydrous rare-earth phosphates, monazite and xenotime: a review.

The synthesis methods, crystal structures, and properties of anhydrous monazite and xenotime (REPO4) crystalline materials are summarized within this review. For both monazite and xenotime, currently available Inorganic Crystal Structure Database data were used to study the effects of incorporating different RE cations on the unit cell parameters, cell volumes, densities, and bond lengths. Domains of monazite-type and xenotime-type structures and other AXO4 compounds (A = RE; X = P, As, V) are discussed with respect to cation sizes. Reported chemical and radiation durabilities are summarized. Different synthesis conditions and chemicals used for single crystals and polycrystalline powders, as well as first-principles calculations of the structures and thermophysical properties of these minerals are also provided.

Effects of MgO-RE2O3 and SiO2-RE2O3 (RE = La, Nd, Gd, Ho and Lu) complex sintering additives on the phase composition, microstructure and mechanical properties of dual-phase Si3N4 ceramics

Dual-phase (α+β)-Si3N4 ceramics with MgO-RE2O3 and SiO2-RE2O3 (RE = La, Nd, Gd, Ho and Lu) complex sintering additives were prepared by SPS at 1650 and 1700 °C. The effect of sintering additives on the phase transition, microstructure evolution and mechanical properties of the Si3N4 ceramics were studied. For the MgO-RE2O3 samples, as the RE radius increased, the phase transition was decelerated, the percentage of rod-like grains and fracture toughness decreased and the hardness showed a hill-shape curve. It is proposed that the effect of RE radius is connected with the segregation behavior of RE cations on the surface of Si3N4 grains. For the SiO2-RE2O3 samples, as the RE radius increased, the phase transition was accelerated and the percentage of rod-like grains increased. It is suggested that the effect of RE radius is related with the liquid phase viscosity and nitrogen solubility.

Doping rare earth cations with an additional chemical reduction synergistically weakened the photocatalytic performance of ceria.

Chemical reducing or rare earth cations (RE) doping was normally employed to promote the photocatalytic performance of ceria, aimed to evaluate their cooperation influences, ceria was obtained by decomposing homogenously RE (RE = La, Sm, and Y)-doped CeCO3OH in H2. XPS and EPR results evidenced that the excess oxygen vacancies (OVs) were formed in RE-doped CeO2 compared to the un-doped ceria. However, all the RE-doped ceria unexpectedly showed an impeded photocatalytic activity towards to methylene blue (MB) photodegradation. The 5% Sm-doped ceria had the best MB photodegradation ratio of 81.47% after 2-h reaction in all RE-doped samples, which was lower than that of 87.24% for the un-doped ceria. After doping RE cations and chemical reducing, the band gap of ceria were almost narrowed, while the PL spectra and photo-electro characterizations indicated that the separation efficiency of photo-excited e-/h+ (electrons/holes) was reduced. The RE dopants and formed excess OVs including inner and surface OVs was proposed to promote the recombination of e-/h+ which further hindered the generation of active species of ·O2- and ·OH, and finally weakened the photocatalytic activity of ceria.

Thermochemistry of sodium rare earth ternary fluorides, NaREF4

Sodium rare earth fluorides, NaREF4 (RE = rare earth), are used as luminescent materials for light emission and biomedical applications and are important compositions for extracting and separating RE elements. Solution calorimetric measurements of a series of β-structured NaREF4 (Na1.5RE1.5F6) phases with various RE elements determined their heats of formation. Though the lattice contracts from light to heavy RE elements, NaREF4 compounds show more exothermic enthalpies of formation from binary components with the decrease of RE3+ radii, contrary to behavior seen in most RE oxide ternary compounds. By constructing Born–Haber cycles, the different slopes of lines relating lattice energies to lattice parameters in binary and ternary fluorides appear to be the reason for this reverse trend, which can be associated with changes in the coordination number of RE cations. These trends and the metastability of sodium light RE fluorides not only reveal the key role of ionic radius in RE compound stability, but also are significant for the design and synthesis of new materials and motivate the more effective utilization of RE.

Homogenously Rare-Earth-Ion-Doped Nanoceria Synthesis in KOH-NaOH Molten Flux: Characterization and Photocatalytic Property

Homogeneously rare-earth (RE=La, Sm and Y) ions doped CeO2 nanoparticles (NPs) with enhanced photocatalytic performance were synthesized by a facile KOH-NaOH molten flux method. XRD, TEM, EDS mapping and XPS results demonstrate that RE cations have been successfully doped into the CeO2 lattice, which leads to the lattice expansion/shrinking, and more oxygen vacancies are generated after RE ions doping. The UV-Vis DRS and PL spectra indicate that RE-doped CeO2 samples have slightly narrower band gaps and significantly reduced photo-generated electron-hole recombination rates. 5% RE ions doped CeO2 NPs show excellent photocatalytic performances and the photodegradation ratio of methylene blue (MB) increases from 71.63% of undoped CeO2 to 76.35%, 77.51% and 77.37% for 5%-La, 5%-Sm and 5%-Y-doped CeO2 NPs, respectively. The obviously reduced recombination rate of e−/h+ pairs after RE ions doping may be the critical factor for the enhanced photocatalytic performance.

Rare-earth indium selenides RE3InSe6 (RE = La−Nd, Sm, Gd, Tb): Structural evolution from tetrahedral to octahedral sites

The ternary rare-earth indium selenides RE3InSe6 have been prepared by reactions of the elements at 850 ​°C and the range of rare-earth substitution has been determined to be RE ​= ​La−Nd, Sm, Gd, Tb. Single crystals of La3InSe6, Ce3InSe6, and Nd3InSe6, obtained in the presence of KBr flux, were analyzed by X-ray diffraction, which revealed an orthorhombic structure in space group Pnnm with Z ​= ​4 and cell parameters of a ​= ​14.4722(18)−14.2793(11) Å, b ​= ​17.636(2)−17.4401(14) Å, and c ​= ​4.2123(5)−4.1013(3) Å. The structure consists of two types of linear stacks built from In-centred polyhedra, which are separated by the RE cations in seven and eightfold coordination. Careful examination of the In sites shows that there is a gradual evolution from the noncentrosymmetric La3InS6-type (space group P21212, adopted by most of the sulfides RE3InS6) to the centrosymmetric U3ScS6-type structure (space group Pnnm, adopted by most of the selenides RE3InSe6). Diffuse reflectance spectroscopy showed that all members of RE3InSe6 are semiconductors with optical band gaps of 1.2–1.4 ​eV. Magnetic measurements indicated that La3InSe6 is diamagnetic and Nd3InSe6 is paramagnetic with no transitions occurring down to 2 ​K.

CoFe2-xRExO4 (RE=Dy, Yb, Gd) magnetic nanoparticles for biomedical applications

Nanoparticles with general formula CoFe2-xRExO4 (RE = Yb, Dy, Gd; x = 0.0–0.3) were synthesized by the co-precipitation and heat treated for potential application in magnetic hyperthermia. The influence of RE doping on structural, magnetic and thermal properties has been investigated. The RE cations enter the spinel lattice as detected by X-ray diffraction. Thermal treatment leads to thermodynamically stable and relaxed single-phase spinel structures only for lower RE content, x = 0.01–0.05. The annealed samples present higher mass magnetization values up to 83 Am2/kg. In the case of annealed samples saturation magnetization decreases linearly from 83 Am2/kg (x = 0.01) to about 60 Am2/kg (x = 0.30). Thermal treatment induces a reduction in coercivity from 60 to 100 mT for as-prepared samples to 18–33 mT for annealed samples. Heating efficiency, i.e., Specific Loss Power of all samples has been studied using both magnetometric and calorimetric method to examine the energy loss mechanisms.

Thermochemistry of Sodium Rare Earth Ternary Fluorides, NaREF <sub>4</sub>

Sodium rare earth fluorides, NaREF4 (RE = rare earth), are used as luminescent materials for light emission and biomedical applications and are important compositions for extracting and separating RE elements. Solution calorimetric measurements of a series of β-structured NaREF4 (Na1.5RE1.5F6) phases with various RE elements determined their heats of formation. Though the lattice contracts from light to heavy RE elements, NaREF4 compounds show more exothermic enthalpies of formation from binary components with decrease of RE3+ radius, contrary to behavior seen in most RE oxide ternary compounds. By constructing Born–Haber cycles, the different slopes of lines relating lattice energies to lattice parameters in binary and ternary fluorides appear to be the reason for this reverse trend, which can be associated with changes in the coordination number of RE cations. These trends and the metastability of sodium light RE fluorides not only reveal the key role of ionic radius in RE compound stability, but also are significant for the design and synthesis of new materials and motivate the more effective utilization of RE.

Crystal structures and comparisons of potassium rare-earth molybdates KRE(MoO4)2 (RE = Tb, Dy, Ho, Er, Yb, and Lu).

Six potassium rare-earth molybdates KRE(MoO4)2 (RE = Tb, Dy, Ho, Er, Yb, and Lu) were synthesized by flux-assisted growth in K2Mo3O10. The crystal structures were determined using single-crystal X-ray diffraction data. The synthesized molybdates crystallize with the ortho-rhom-bic Pbcn space group (No. 60). Trendlines for unit-cell parameters were calculated using data from the current study. The unit-cell parameters a and c increase linearly whereas b decreases with larger RE cations, based on crystal radii. The unit-cell volumes increase linearly and the densities decrease linearly with larger RE cations. The average distances between the RE cations and the nearest O atoms increase with larger cations whereas the average distances of Mo-O and K-O do not show specific trends.

Syntheses and Crystal Structures of Rare-Earth Oxyapatites Ca2RE8(SiO4)6O2 (RE = Pr, Tb, Ho, Tm)

Four different rare-earth oxyapatites of Ca2RE8(SiO4)6O2 (RE = Pr, Tb, Ho, Tm) were synthesized using a solution-based method followed by drying, calcination, and high-temperature sintering in air. X-ray powder diffraction and Raman spectroscopy were performed on the synthesized oxyapatites. The RE oxyapatites crystallize in the hexagonal space group P63/m with similar unit cell parameters, increasing linearly with larger RE cations. The unit cell volumes increase linearly whereas the densities decrease nonlinearly with larger RE cations. Raman spectra showed intense bands of the symmetric bending and stretching modes of SiO4 at ~ 400 and 860 cm−1 regions, respectively. The bands generally shifted to higher frequencies with smaller RE cations in the structures. Rare-earth oxyapatites Ca2RE8(SiO4)6O2 (RE = Pr, Tb, Ho, Tm) crystallize in the hexagonal space group P63/m, and their unit cell parameters increase linearly with larger RE cations.

Rare‐earth titanate melt structure and glass formation

AbstractThe structure of rare‐earth titanate melts and glasses of composition 17RE2O3.83TiO2 have been investigated in situ by aerodynamic levitation with laser heating. Ti K‐edge X‐ray absorption near‐edge structure (XANES) spectroscopy reveals an effect of RE cation size on mean Ti‐O coordination numbers (nTiO), which increase from ∼4.8(2) in glass‐forming La titanate to ∼5.1(2) in non‐glass‐forming Sc titanate liquids. We suggest that the associated increase in OTi3 triclusters in melts bearing smaller RE cations tends to inhibit glass formation. Both XANES and high‐energy X‐ray diffraction indicate increases in nTiO as the liquids supercool and vitrify. Results are discussed in the context of alkali and alkaline‐earth titanate glasses, extending the observed dependence of nTiO on structural basicity (modifier content divided by potential) to trivalent modifiers and the molten state. We suggest that the most stable titanate glasses form close to compositions where, on average, two oxygen anions bond to each titanium, allowing a continuous, disordered Ti‐O network of bridging oxygen (OTi2), or with equal numbers of OTi3 triclusters and OTi1 non‐bridging oxygen in charge‐balance. We report on new glasses formed from praseodymium, europium, and gadolinium titanate melts, the latter being the smallest rare‐earth for which binary titanate glasses have been obtained.

Three Types of Mixed Alkali‐Metal‐, Transition‐Metal‐, or Rare‐Earth‐Substituted Sandwich‐Type Arsenotungstates with Supporting Rare‐Earth Pendants

Three types of mixed alkali‐metal‐, transition‐metal‐, or rare‐earth‐substituted sandwich‐type arsenotungstates with supporting rare‐earth pendants, namely, [La(H2O)8]2H[K2LaCu3(H2O)9][B‐α‐AsW9O33]2·17H2O (1), Na2K0.5RE0.5[RE(H2O)8][K3Cu2WO(H2O)10][B‐α‐AsW9O33]2·14H2O [RE = Pr3+ (2), Nd3+ (3), Sm3+ (4), Eu3+ (5)], and K2H[Pr(H2O)6][Pr(H2O)7][K2NaCu3(H2O)7][B‐α‐AsW9O33]2·18H2O (6), were synthesized in aqueous solution. The utilization of different alkali‐metal cations led to the formation of three structural types. If only K+ cations were utilized in the system, 1 was obtained, whereas 2–6 formed when Na+ and K+ cations were used. In addition, the common characteristic of 1–6 is that they consist of hexanuclear heterometal‐substituted sandwich‐type arsenotungstate structural units, and the hexanuclear heterometallic clusters in the central belt are distributed in a triangular fashion. The solid‐state photoluminescence spectra of 2, 3, 4, and 5 at ambient temperature are mainly derived from the f–f electron transitions of the RE cations. The drug activities of 4 and 5 were measured through 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assays, and the results demonstrate that 4 can induce the apoptosis of HepG2 cells and HCT‐116 cells through the activation of caspase‐3 and the autophagy of HepG2 cells and HCT‐116 cells through the involvement of lysosomes. The coexistence of apoptosis and autophagy leads to the death of cancer cells.

Electronic phase diagram of half-doped perovskite manganites on the plane of quenched disorder versus one-electron bandwidth

For half-doped manganese oxides that have a perovskite structure, $R{E}_{1\ensuremath{-}\mathrm{x}}A{E}_{\mathrm{x}}\mathrm{Mn}{\mathrm{O}}_{3}$ ($x=0.5$) (RE and AE are rare-earth and alkaline-earth elements, respectively), the phase competition (stability) between the antiferromagnetic charge- or orbital-ordered insulator (CO/OO AFI), ferromagnetic metal (FM), layered (A-type) antiferromagnetic phase [AF(A)], and spin-glass-like insulator (SGI), have been studied using single crystals prepared by the floating zone method. The CO/OO AFI, FM, AF(A), and SGI are displayed on the plane of the disorder (the variance of the RE and AE cations) versus the effective one-electron bandwidth (the averaged ionic radius of the RE and AE). In the plane of the disorder versus the effective one-electron bandwidth, similar to the phase diagram of $R{E}_{1\ensuremath{-}\mathrm{x}}A{E}_{\mathrm{x}}\mathrm{Mn}{\mathrm{O}}_{3}$ ($x=0.45$), the CO/OO AFI, FM, and SGI dominate at the lower-left, right, and upper regions, respectively. However, the CO/OO AFI for $x=0.5$ is more stable than that for $x=0.45$, and it expands to the plane points that correspond to the $R{E}_{0.5}\mathrm{S}{\mathrm{r}}_{0.5}\mathrm{Mn}{\mathrm{O}}_{3}$ ($RE=\mathrm{Nd}$ and Sm) specimens as the hole concentration is commensurate with the ordering of $\mathrm{M}{\mathrm{n}}^{3+}$/$\mathrm{M}{\mathrm{n}}^{4+}$ with a ratio of 1/1. The $y$-dependent electronic phases for $R{E}_{0.5}{(\mathrm{S}{\mathrm{r}}_{1\ensuremath{-}\mathrm{y}}\mathrm{B}{\mathrm{a}}_{\mathrm{y}})}_{0.5}\mathrm{Mn}{\mathrm{O}}_{3}$ ($0\ensuremath{\le}y\ensuremath{\le}0.5$) ($RE=\mathrm{Sm}$, $\mathrm{N}{\mathrm{d}}_{0.5}\mathrm{S}{\mathrm{m}}_{0.5}$, Nd, and Pr) show that the AF(A) intervenes between the CO/OO AFI and FM. Besides the region around ${(\mathrm{L}{\mathrm{a}}_{1\ensuremath{-}\mathrm{y}}\mathrm{P}{\mathrm{r}}_{\mathrm{y}})}_{0.5}\mathrm{S}{\mathrm{r}}_{0.5}\mathrm{Mn}{\mathrm{O}}_{3}$ ($0\ensuremath{\le}y\ensuremath{\le}1$) that has a smaller disorder, the AF(A) also exists at the regions around $R{E}_{0.5}{(\mathrm{S}{\mathrm{r}}_{1\ensuremath{-}\mathrm{y}}\mathrm{B}{\mathrm{a}}_{\mathrm{y}})}_{0.5}\mathrm{Mn}{\mathrm{O}}_{3}$ ($0lyl0.3$) ($RE=\mathrm{Sm}$ and $\mathrm{N}{\mathrm{d}}_{0.5}\mathrm{S}{\mathrm{m}}_{0.5}$) that have a relatively larger disorder. This indicates that the AF(A) is rather robust against the increased disorder, even though an ordering of the (${x}^{2}\ensuremath{-}{y}^{2}$) orbital occurs. This study has comprehensively investigated the effects of the disorder on the AF(A) as well as on the competition between the CO/OO AFI, FM, and AF(A) that is unique to $x=0.5$. The comparison of phase diagrams between $x=0.45$ and 0.5 brings further insights into the understanding of the rich electronic phases of manganites.

Influence of the concentration and lanthanoide type on the phase transitions in Ln2O3-MO2 system (Ln = La, Gd, Y; M = Zr, Hf)

Influence of the concentration and type of rare-earth oxide on the chemical composition and structure of the compounds formed in the “Ln2O3-MO2” system has been investigated by X-ray powder diffraction and Raman spectroscopy. It was found that crystallization temperature of synthesized powders rises with an increase in the concentration of Ln2O3. Besides, it was revealed that the efficiency of stabilization of high-temperature phases (tetragonal and cubic) in Ln2O3-ZrO2 systems increases with the introduction of RE cations in the La3+ → Gd3+ → Y3+ series in accordance with the increase in the solubility of Ln2O3 in ZrO2. A similar behavior was also observed for the Ln2O3-HfO2 systems. Finally, we established that the compounds formed in Ln2O3-HfO2 systems have a greater ability to crystallize in the monoclinic phase.

Rare-Earth-Incorporated Tellurotungstate Hybrids Functionalized by 2-Picolinic Acid Ligands: Syntheses, Structures, and Properties.

A series of organic-inorganic rare-earth-incorporated tellurotungstate hybrids, Na4[RE2(H2O)4(pica)2W2O5][(RE(H2O)W2(Hpica)2O4)(B-β-TeW8O30H2)2]2·38H2O (RE = LaIII (1), CeIII (2), NdIII (3), SmIII (4), EuIII (5); Hpica = 2-picolinic acid), were prepared via a one-step assembly reaction of Na2WO4·2H2O, RE(NO3)3·6H2O, K2TeO3, Hpica, and triethylamine (tea). Notably, the solubilization of tea toward Hpica and the solubilization of Hpica toward RE cations in the reaction system play an important role in the formation of 1-5. The most significant feature of 1-5 consists of an intriguing tetrameric [RE2(H2O)4(pica)2W2O5][(RE(H2O)W2(Hpica)2O4)(B-β-TeW8O30H2)2]24- polyoxoanion constructed from two tetravacant Keggin sandwich-type [(RE(H2O)W2(Hpica)2O4)(B-β-TeW8O30H2)2]5- entities linked by a RE-W-Hpica {RE2(H2O)4(pica)2W2O5}6+ cluster, in which Hpica ligands not only play a key bridging role in linking RE and W centers by carboxylic groups in an irregular N-O-RE-O-W-O six-membered-ring motif but also can directly chelate with W centers via N and O atoms in a stable N-O-C-O-W five-membered-ring fashion. 1-5 represent rare organic-inorganic hybrid RE-substituted tellurotungstates. Moreover, the solid-state photoluminescence properties of 3-5 have been deeply investigated, and these compounds exhibit the characteristic emission stemming from intra-4f transitions of RE ions. The energy transfer of the O → W transitions sensitizing the emission of SmIII centers in 4 is convincingly proved by time-resolved emission spectra (TRES); the increase in the strongest typical emission of SmIII ions at a decay time of 17 μs is accompanied by the decline of O → W emission, and the CIE 1931 diagram was obtained from the corresponding TRES. Furthermore, a comparison of the luminescence behaviors of 5 in the solid state and in solution reveals the structural skeletal integrity of 5 in solution and a shorter decay lifetime in the solution caused by the high-frequency O-H oscillators.

Two Families of Rare-Earth-Substituted Dawson-type Monomeric and Dimeric Phosphotungstates Functionalized by Carboxylic Ligands

Two series of novel organic–inorganic hybrid carboxylated rare-earth-substituted monolacunary Dawson-type phosphotungstate monomers [Hdap]4[RE(H2O)(Hpic)3][RE(Hpic)2 (α2-P2W17O61)]·21H2O [RE = GdIII (1), TbIII (2), DyIII (3), HoIII (4), ErIII (5), TmIII (6), YbIII (7), YIII (8); Hpic = 2-picolinic acid, dap = 1,2-diaminopropane] and dimers [H2dap]8[RE2(H2ox)2(ox)(α2-P2W17O61)2]·25H2O [RE = HoIII (9), ErIII (10), TmIII (11), YbIII (12), YIII (13); H2ox = oxalic acid] have been hydrothermally synthesized and characterized by elemental analyses, IR spectra, thermogravimetric measurements, and X-ray single-crystal diffraction. The monomeric polyoxoanion skeleton of isomorphic 1–8 is constructed from a monolacunary Dawson-type phosphotungstate implanted by a [RE1(Hpic)2]3+ cation in the polar position and supported by the other [RE2(H2O)(Hpic)3]3+ cation on the equatorial belt. Interestingly, two kinds of RE cations separately coordinate to two or three Hpic ligands in the form of N–C–C–O–RE containing five-me...

Investigation on the cation location, structure and performances of rare earth-exchanged Y zeolite

A series of Y zeolites exchanged with different amount of cerium and lanthanum cations were investigated. Comprehensive routine analysis tools including X-ray photoelectron spectroscopy (XPS), X-ray fluorescence (XRF), X-ray diffraction (XRD) and Py-Fourier transform infrared spectroscopy (Py-FTIR) were used to identify the cation location, and the result was verified via XRD Rietveld study. The results revealed that almost all the RE cations in RE-4, most cations in RE-8 to RE-14 and part of cations in RE-16 were located in the sodalite cage. The AlIV/(AlV+AlVI) values revealed by 27Al MAS NMR spectra, the silicon aluminum ratio of the framework (SARF) values deduced from 29Si MAS NMR spectra and XRD, and hydroxyl amount were reasonably in accordance with the location and content of rare earth cations. The hydrothermal stability derived from in situ XRD investigation and catalyst activity provided by micro-activity test manifested that samples RE-8 to RE-14 exhibited better performances than RE-4 and RE-16, among which RE-12 had the best properties. The phenomena were interpreted by the cation location and structural properties.

Syntheses, structural characterization and photophysical properties of two series of rare-earth-isonicotinic-acid containing Waugh-type manganomolybdates

Two classes of rare-earth-organic-containing Waugh-type manganomolybdates (NH4)8{[RE(Hina)(ina)(H2O)2][MnIVMo9O32]}2·12H2O [RE = La3+ (1), Pr3+ (2), Nd3+ (3)] and (NH4)3[RE(Hina)2(H2O)6][MnIVMo9O32]·7H2O [RE = Sm3+ (4), Eu3+ (5), Gd3+ (6), Tb3+ (7), Dy3+ (8), Ho3+ (9), Er3+ (10), Tm3+ (11), Yb3+ (12), Y3+ (13)] (Hina = isonicotinic acid) were prepared by means of a step-by-step synthetic strategy and further characterized by IR spectroscopy, elemental analyses, UV-visible spectroscopy and single-crystal X-ray diffraction. X-ray diffraction indicates that 1–3 consist of an organic–inorganic hybrid dimeric {[RE(Hina)(ina)(H2O)2][MnIVMo9O32]}28− core constituted by two [MnMo9O32]6− units linked via a dinuclear {[RE(Hina)(ina)(H2O)2]2}4+ cation whereas 4–13 are composed of an organic–inorganic hybrid [RE(Hina)2(H2O)6]3+ fragment and one [MnMo9O32]6− polyoxoanion. It should be pointed out that the nature of RE cations controls these two structure types. As far as we know, 1–13 represent the first examples of Waugh-type manganomolybdates including rare-earth-organic subunits so far. Furthermore, their photocatalytic activities for the degradation of azophloxine were probed in aqueous medium and 3 and 8 as representatives were systematically investigated involving the influence of the optimal pH, catalyst dosage and the doping amount of VK-TA18 nanometer titanium dioxide on the photocatalytic activities. The solid-state photoluminescence properties and lifetime decay behaviors of 3, 4 and 5 in UV-visible or near-infrared regions were also examined at ambient temperature.

Band-Gap and Band-Edge Engineering of Multicomponent Garnet Scintillators from First Principles

Complex doping schemes in RE$_3$Al$_5$O$_{12}$ (RE=rare earth element) garnet compounds have recently led to pronounced improvements in scintillator performance. Specifically, by admixing lutetium and yttrium aluminate garnets with gallium and gadolinium, the band-gap was altered in a manner that facilitated the removal of deleterious electron trapping associated with cation antisite defects. Here, we expand upon this initial work to systematically investigate the effect of substitutional admixing on the energy levels of band edges. Density functional theory was used to survey potential admixing candidates that modify either the conduction band minimum (CBM) or valence band maximum (VBM). We considered two sets of compositions based on Lu$_3$B$_5$O$_{12}$ where B = Al, Ga, In, As, and Sb; and RE$_3$Al$_5$O$_{12}$, where RE = Lu, Gd, Dy, and Er. We found that admixing with various RE cations does not appreciably effect the band gap or band edges. In contrast, substituting Al with cations of dissimilar ionic radii has a profound impact on the band structure. We further show that certain dopants can be used to selectively modify only the CBM or the VBM. Specifically, Ga and In decrease the band gap by lowering the CBM, while As and Sb decrease the band gap by raising the VBM. These results demonstrate a powerful approach to quickly screen the impact of dopants on the electronic structure of scintillator compounds, identifying those dopants which alter the band edges in very specific ways to eliminate both electron and hole traps responsible for performance limitations. This approach should be broadly applicable for the optimization of electronic and optical performance for a wide range of compounds by tuning the VBM and CBM.

Synthesis and structural characterization of the new rare-earth borosilicates Pr3BSi2O10 and Tb3BSi2O10

Abstract The rare-earth borosilicates RE 3BSi2O10 (RE = Pr, Tb) were synthesized under high-temperature conditions of 1600 °C in a radio frequency furnace from praseodymium oxide, terbium oxide, silicon dioxide, silicon nitride, boron trioxide, and boric acid. The structure determinations based on powder diffraction data revealed that both phases RE 3BSi2O10 (RE = Pr, Tb) are isotypic to Gd3BSi2O10 [L. Chi, H. Chen, X. Lin, H. Zhuang, J. Huang, Jiegou Huaxue 1998, 17, 297]. The compounds crystallize in the orthorhombic space group Pbca (no. 61) with eight formula units and the lattice parameters a = 982.9(2), b = 714.2(2), c = 2314.4(4) pm, V = 1.6247(4) nm3, R p = 0.0231, and R wp = 0.0354 (all data) for Pr3BSi2O10 and a = 960.5(5), b = 692.1(3), c = 2272.4(1) pm, V = 1.5106(2) nm3 for Tb3BSi2O10. The lattice parameters of Tb3BSi2O10 could be determined, but a final refinement of the powder data has not proved satisfactory. The structure of Pr3BSi2O10 exhibits eight- (Pr1) and ninefold coordinated rare-earth cations (Pr2 and 3). Layers of ortho-silicate anions [SiO4]4– and borosilicate anions [BSiO6]5– are arranged alternatingly along the c axis and the RE cations are located in between.