The luminescence of Pr3+ in BaY4Si5O17

The cell constants of four new monoclinic compounds BaR₄X₅O₁₇ (R = Y, Gd; X = Si, Ge) are given. The luminescence of various RE activators in the silicates is reported. Pr³⁺-activated BaY₄Si₅O₁₇ shows efficient ultraviolet 5d → 4f emission and weak 4f → 4f emission (mainly red luminescence from the ¹D₂ level). The 5d → 4f emission is ascribed to Pr³⁺ on Y sites, the 4f → 4f emission to Pr³⁺ on Ba sites. Energy transfer from Pr³⁺ to Gd³⁺ has been observed. Gd³⁺ plays an intermediate role in the energy transfer from Pr³⁺ to Sm³⁺ and to Dy³⁺ in BaGd₄Si₅O₁₇. Upon activation with Tb³⁺ the silicates show characteristic green Tb³⁺ luminescence with a quantum efficiency of 75% for ultraviolet excitation.     

Magnetic Behavior of R2Ba2CuPtO8 Oxides (R=Ho, Er, Tm, Yb, Lu, and Y)

Magnetic properties of polycrystalline R₂Ba₂CuPtO₈ (R=Ho, Er, Tm, Yb, Lu and Y) oxides have been studied from magnetization and magnetic susceptibility measurements. The lutetium and yttrium oxides behave as antiferromagnets and the estimated Néel temperatures are 5.2 and 5.7 K, respectively. In the case of the remaining R₂Ba₂CuPtO₈ oxides, Cu²⁺ and R³⁺ become antiferromagnetically ordered simultaneously, with the exception of TmBa₂CuPtO₈, where the χ vs T plot exhibits two maxima at 8 and 5 K, which have been assigned to the Néel temperatures of Cu²⁺ and Tm³⁺ sublattices, respectively. Taking into account the structure, a superexchange mechanism of the type R-O-Cu-O-R has been proposed in which the Cu²⁺ sublattice plays an important role as promoter of the antiferromagnetic interactions of ferromagnetically R³⁺ coupled in the a-c plane of the structure. Field-induced metamagnetic transitions have been observed below the Néel temperature in all cases; however, different critical fields are achieved depending on the nature of R³⁺ ions.     

Alteration of rare-earth-metal cluster iodides R(R6I12Z) through cation substitution

Four examples of (A_xR_1−x)R₆I₁₂Z phases further illustrate the flexibility of the rhombohedral R₇X₁₂Z structure to substitution of heterocations for the isolated R^III atoms without destruction of the structure. The examples with R=La, Pr, Z=Fe, Co, Ir, and stoichiometric amounts of A=Na or Ca were prepared by traditional high temperature techniques and characterized by single crystal and Guinier powder X-ray diffraction techniques. Product compositions refined in the parent space group from reactions of stoichiometry AR₆I₁₂Z were (Na_0.90Pr_0.10)Pr₆I₁₂Ir, (Na_0.954La_0.046)La₆I₁₂Fe, and (Ca_0.801La_0.199)La₆I₁₂Co. More general characteristics of and trends in the family of R₇X₁₂Z structures are also considered, including distortions of the ideal motif as a function of extremes in the components.     

Ferrimagnetism in the rare earth titanium (III) oxides, RTiO3; R = Gd,Tb, Dy,Ho, Er,Tm

The series of compounds RTiO₃, R = Gd, Tb, Dy, Ho, Er, and Tm, were obtained as single-phase materials via solid state reaction between Ti₂O₃ and R₂O₃ at ca. 1500°C in welded molybdenum crucibles under argon; YbTiO₃ and LuTiO₃ could not be obtained as single-phase materials using this procedure. Lattice constants for all compounds were determined from powder X-ray data and are compared with previous results. All of these materials order magnetically between 30 and 70 K. From the appearance of the χ^?1_m vs T curve the type of order can be identified as ferrimagnetic. High-temperature susceptibility data have been fit to a two-sublattice molecular field model and the intra- and intersublattice interaction constants have been extracted. It is found that the TiTi interaction is ferromagnetic and relatively constant from R = Gd to R = Lu. Low-temperature magnetization field data suggest the existence of complex magnetic structures, large magnetocrystalline anisotropy, or both. The magnetic properties of the RTiO₃ series are compared to those of the chemically similar and better-known RMO₃ phases where M = Al, V, Cr, Mn, and Fe. The observed differences are shown to follow from the sign of the M-M interaction, which is ferromagnetic for M = Ti and antiferromagnetic for M = V, Cr, Mn, and Fe, together with the implications of the crystal symmetry for the R-M interaction.     

Photoluminescence of Eu-doped triple phosphate Ca8MgR(PO4)7 (R=La, Gd, Y)

Eu³⁺-doped triple phosphate Ca₈MgR(PO₄)₇ (R=La, Gd, Y) was synthesized by the general high-temperature solid-state reaction. Excitation and emission spectra as well as luminescence decay were used to characterize the phosphors. Photoluminescence excitation and emission spectra showed that the phosphor could be efficiently excited by UV-vis light from 260 to 450 nm to give bright red emission assigned to the transition (⁵D₀→⁷F₂) at 612 nm. The richness of the red color has been verified by determining their color coordinates (X, Y) from the CIE standard.     

R-site varied series of RBaCo2O5.5 (R2Ba2Co4O11) compounds with precisely controlled oxygen content

The entire family of carefully oxygen-adjusted RBaCo₂O_5.5 or R₂Ba₂Co₄O₁₁ (R=Y, Ho-La) double-perovskite oxides is systematically investigated for the lattice parameters, A-site cation disorder, and characteristic physical properties, i.e. the metal-insulator transition, ferromagnetic transition and so-called metamagnetic transition. With increasing size of the R constituent, the lattice parameters start to deviate from the linear behavior, indicating partial oxygen/vacancy and A-site cation disorder for the largest Rs of Nd, Pr and La. Both the metal-insulator transition and the two magnetic transitions are found to be highly sensitive to even minor deviations from the ideal 5.5 oxygen stoichiometry, thus underlining the importance of proper oxygen-content adjustment.     

Structure and magnetism of rare-earth-substituted Ca3Co2O6

Yttrium- and rare-earth-substituted derivatives of Ca_3−vR_vCo₂O₆ (RY, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb, and Lu) have been synthesized and structurally characterized by powder X-ray and neutron diffraction. All phases adopt the K₄CdCl₆-type structure with space group R3¯c), in which the trivalent R³⁺ substituents randomly occupy the Ca²⁺ site. The homogeneity range of Ca_3−vR_vCo₂O₆ extends to v≈0.90 for the substituents concerned. A significant increase in the Co2-O distances within the trigonal-prismatic Co2O₆ co-ordination polyhedra upon introduction of R³⁺ confirms that extra electrons from the R³⁺-for-Ca²⁺ substitution exclusively enter the Co2 site of the quasi-one-dimensional Ca_3−vR_vCo₂O₆ structure, thereby formally reducing its oxidation state. This is furthermore supported by magnetic susceptibility and low-temperature neutron diffraction measurements. The long-range ferrimagnetic ordering temperature is reduced upon R substitution and appears to vanish for v>∼0.30.     

Synthesis and VUV-UV spectroscopic properties of rare earth borosilicate oxyapatite: RE5Si2BO13:Ln (RE=La, Gd, Y; Ln=Eu, Tb)

Three rare earth borosilicate oxyapatites, RE₅Si₂BO₁₃ (RE=La, Gd, Y), were synthesized via wet chemical method, of which RE₅Si₂BO₁₃ (RE=Gd, Y) were first reported in this work. In the three oxyapatites, [BO₄] and [SiO₄] share the [TO₄] tetrahedral oxyanion site, and RE³⁺ ions occupy all metal sites. The differential scanning calorimetry-thermo gravimetry measurements and high temperature powder X-ray diffraction pattern revealed a vitrification process within 300-1200 °C, which was due to the glass-forming nature of borosilicates. From the VUV excitation spectra of Eu³⁺ and Tb³⁺ in RE₅Si₂BO₁₃, the optical band gaps were found to be 6.31, 6.54 and 6.72 eV for RE₅Si₂BO₁₃ (RE=La, Gd, Y), respectively. The emission and excitation bands of Eu³⁺ and Tb³⁺ are discussed relating with their coordination environments. Among the three hosts, Y₅Si₂BO₁₃ would be the best for Eu³⁺ and Tb³⁺-doped phosphors.     

Synthesis and crystal structure of RMgSi2 compounds (R=La, Ce, Pr, Nd), a particular example of linear intergrowth

A new series of rare earth compounds with stoichiometry RMgSi₂ (R=La, Ce, Pr, Nd) is reported. The single crystal X-ray diffraction showed that CeMgSi₂, which melts congruently at 1200 °C, crystallizes in a new tetragonal structure type (I4₁/amd, tI32, a=4.2652(4) Å, c=36.830(4) Å, Z=8; wR₂=0.042 (19 parameters, 393F₀²), R₁=0.018 (297F₀>4σF₀). The crystal structure of CeMgSi₂ can be formally built up by alternating along the z direction four CeMg₂Si₂-type CeMg₂Si₂ slabs with four AlB₂-type CeSi₂ slabs, one after the other. The structural model obtained from a CeMgSi₂ single crystal has been confirmed for the La, Pr and Nd homologous compounds by means of Rietveld refinement. The trend of the unit-cell parameters, plotted versus the R³⁺ ionic radius, shows a linear behaviour, which strongly suggests a trivalent state for the Ce atoms. An analysis of the features of this new structure is reported, in comparison with the other known CeMg₂Si₂/AlB₂-type linear intergrowth compounds.     

Synthesis and Spectroscopic [Electronic,IR, NMR (1H, 13C, 89Y)] Characterization of Hexaisopropoxoniobates and ‐Tantalates of Yttrium(III) and Lanthanides(III)

Hexaisopropoxoniobates/tantalates of lathanides of the type [Ln{(μ‐OPrⁱ)₂M(OPrⁱ)₄}₃] (M = Nb, Ln = Y( 1 ), La( 2 ), Nd( 3 ), Er( 4 ), Lu( 5 ); M = Ta, Ln = Y( 6 ), Gd( 7 )) have been prepared by the reactions of LnCl₃.3PrⁱOH with three equivalents of KM(OPrⁱ)₆ in benzene. Reactions in 1:2 molar ratio of LnCl₃.3PrⁱOH with KTa(OPrⁱ)₆ yielded derivatives of the type [{(PrⁱO)₃Ta(μ‐OPrⁱ)₃}Ln{(μ‐OPrⁱ)₂Ta(OPrⁱ)₄}(Cl)] (Ln = Y( 8 ), Gd( 9 )), which on interactions with one equivalent of KOPrⁱ afforded [{(PrⁱO)₃Ta(μ‐OPrⁱ)₃}Ln {(μ‐OPrⁱ)₂Ta(OPrⁱ)₄}(OPrⁱ)] (Ln = Y( 10 ), Gd( 11 )). All these derivatives have been characterized by elemental analyses and molecular weight measurements as well as by their spectroscopic [IR, ¹H and ¹³C NMR (Y, La, Lu), electronic (Nd, Er)] studies. ⁸⁹Y NMR studies have also been carried out on derivatives ( 6 ), ( 8 ), and ( 10 ).     

Photoluminescence of Ce, Pr and Tb activated Sr3Ln(PO4)3 under VUV-UV excitation

The spectroscopic properties in VUV-Vis range for the eulytite structural phosphors Sr₃Gd(PO₄)₃:Ln³⁺ (Ln³⁺=Ce³⁺, Pr³⁺, Tb³⁺), Sr₃Ce(PO₄)₃, Sr₃Gd(PO₄)₃ and Sr₃Tb(PO₄)₃ were investigated. The bands near 170 nm in VUV excitation spectra are assumed to connect with the host lattices related absorption. The f-d transitions of Ce³⁺, Pr³⁺ and Tb³⁺ in the host lattices are assigned and corroborated. A convenient experiment formulation on the relationship between the lowest f-d transition energies and n value for trivalent 4fⁿ-series rare earth ions in these host lattices is applied.     

RE/TiO2光催化剂的谱学特性与气相光催化性能的研究

采用改进的sol-gel法和浸渍法制备了TiO₂掺杂稀土离子La³⁺、Y³⁺、Gd³⁺、Er³⁺、Nd³⁺、Pr³⁺的RE/TiO₂光催化剂,运用FTIR、XRD、TEM、低温氮吸附/脱附、TG/DTA、UV-Vis DRS、表面光电压谱(SPS)等进行表征,以气相光催化降解乙烯、溴代甲烷作为探针反应,阐明了RE/TiO₂光催化剂的谱学特性与气相光催化性能的关系。结果显示,稀土离子掺杂后,TiO₂的锐钛矿含量增加,比表面积增大,粒径变小,吸收边发生蓝移,表面光电压的响应阈值增大,此外,Pr³⁺除外的其它稀土离子掺杂的TiO₂的表面光电压信号增强;光催化降解实验表明,与纯TiO₂相比,La³⁺、Y³⁺、Gd³⁺、Er³⁺、Nd³⁺掺杂TiO₂样品上乙烯、溴代甲烷的光催化活性均有不同程度的增强,而且表现出较强的矿化能力。但是,掺杂Pr³⁺的TiO₂的光催化性能降低恰好对应较弱的表面光电压信号。所以,本文认为提高光生电子-空穴对的分离效率是改善光催化性能的关键因素。     

Mossbauer Investigation of Fe-Doped Ni(III) Perovskites ANi0.98Fe0.02O3 (A=Pr, Nd, Sm, Y, Lu, Tl) versus Temperature

Nickelates ANiO₃ (A=Pr, Nd, Sm, Lu, Y, Tl) containing Mössbauer probe ⁵⁷Fe atoms were synthesized. In the case of nickelates with larger rare earth (A=Pr, Nd, Sm) the Mössbauer spectra confirm that ferric ions are located in single type of crystallographic positions. On the contrary, the spectra of ANi_0.98Fe_0.02O₃ with small cations (A=Lu, Y, Tl) can be described as a superposition of two sub-spectra which indicate that ⁵⁷Fe probe atoms are simultaneously stabilized in two non-equivalent crystallographic positions. These results have been interpreted in terms of partial charge disproportionation of Ni³⁺ cations associated with the electronic localization in monoclinic distorted Lu, Y, Tl nickelates. The modification of ⁵⁷Fe spectra for TlNi_0.98Fe_0.02O₃ as a function of temperature has shown that this charge disproportionation occurs in varying degrees, corresponding to the charge states Fe^(3+σ)+ and Fe^(3−σ′)+. On the contrary, the spectra for Lu and Y nickelates show that charge variation (σ,σ′) for dopant Fe(1) and Fe(2) cations does not depend on temperature.     

The crystal structure of the monohydrate R2Mo6O21·H2O (R=Pr, Nd, Sm, and Eu): a layer structure containing disordered [Mo2O7] groups

Although R₂O₃:MoO₃=1:6 (R=rare earth) compounds are known in the R₂O₃-MoO₃ phase diagrams since a long time, no structural characterization has been achieved because a conventional solid-state reaction yields powder samples. We obtained single crystals of R₂Mo₆O₂₁·H₂O (R=Pr, Nd, Sm, and Eu) by thermal decomposition of [R₂(H₂O)₁₂Mo₈O₂₇]·nH₂O at around 685-715 °C for 2 h, and determined their crystal structures. The simulated XRD patterns of R₂Mo₆O₂₁·H₂O were consistent with those of previously reported R₂O₃:MoO₃=1:6 compounds. All R₂Mo₆O₂₁·H₂O compounds crystallize isostructurally in tetragonal, P4/ncc (No. 130), a=8.9962(5), 8.9689(6), 8.9207(4), and 8.875(2) Å; c=26.521(2), 26.519(2), 26.304(2), and 26.15(1) Å; Z=4; R₁=0.026, 0.024, 0.024, and 0.021, for R=Pr, Nd, Sm, and Eu, respectively. The crystal structure of R₂Mo₆O₂₁·H₂O consists of two [Mo₂O₇]²⁻-containing layers (A and B layers) and two interstitial R(1)³⁺ and R(2)³⁺ cations. Each [Mo₂O₇]²⁻ group is composed of two corner-sharing [MoO₄] tetrahedra. The [Mo₂O₇]²⁻ in the B layer exhibits a disorder to form a pseudo-[Mo₄O₉] group, in which four Mo and four O sites are half occupied. R(1)³⁺ achieves 8-fold coordination by O²⁻ to form a [R(1)O₈] square antiprism, while R(2)³⁺ achieves 9-fold coordination by O²⁻ and H₂O to form a [R(2)(H₂O)O₈] monocapped square antiprism. The disorder of the [Mo₂O₇]²⁻ group in the B layer induces a large displacement of the O atoms in another [Mo₂O₇]²⁻ group (in the A layer) and in the [R(1)O₈] and [R(2)(H₂O)O₈] polyhedra. A remarkable broadening of the photoluminescence spectrum of Eu₂Mo₆O₂₁·H₂O supported the large displacement of O ligands coordinating Eu(1) and Eu(2).     

Crystal structures and thermal properties of some rare earth alkoxides with tertiary alcohols Possible precursors for atomic layer deposition of rare earth oxides

Rare earth (RE) alkoxides of Y, La, Pr, and Gd were synthesized using three tertiary alcohols namely 2,3-dimethyl-2-butanol, 2,2-dimethyl-3-ethyl-3-pentanol, and 3-isopropyl-2,4-dimethyl-pentan-3-ol. ¹H and ¹³C NMR, elemental analysis (CHN) and MS were used to characterize the complexes. New crystal structures of dimeric [Y(OCEt₂ ^t Bu)₃]₂, [La(OCEt₂ ^t Bu)₃]₂, [Gd(OC ⁱ Pr₃)₃]₂, and [La(OC ⁱ Pr₃)₃]₂ were solved. Thermal properties of these compounds were studied with TG/SDTA and vacuum sublimation experiments. With all the cations Y, La, Pr, and Gd, the compounds with smallest ligand ⁱ PrMe₂CO⁻ seem to be the most volatile. The compounds with larger alkoxo ligands have lower volatility but their thermal stability is better. Atomic layer deposition experiments showed that RE oxide thin films could be grown from these alkoxides using water as the oxygen precursor.     

Über Sauerstoffperowskite mit fünf- und vierwertigem Iridium Verbindungen vom Typ Ba2B3+Ir5+O6 und Ba3B3+Ir4,5+2O9

Perovskites with pentavalent iridium of type Ba₂B³⁺Ir⁵⁺O₆ are for B³⁺ = La, Nd, Sm, Gd, Dy, Y cubic and with B³⁺ = In hexagonal (6 L structure of BaTiO₃ type; sequence (hcc)₂). According to the intensity calculations of powder patterns for Ba₃SmIr₂O₉ and Ba₃YIr₂O₉ the new series Ba₃B³⁺Ir₂O₉ (B³⁺ = Sm, Eu, Gd, Dy, Ho, Yb, Sc, Y, In; mean oxidation state of iridium + 4.5) crystallize in a hexagonal 6 L structure of BaTiO₃ type (space group $\text{P6}{}_3\text{mmc}$; sequence (hcc)₂). The intensity-related R′ value is 8.6% for B³⁺ = Sm and 10.0% for Y. In the octahedral net the double groups of face-connected octahedra are occupied by the iridium atoms, which are dislocated from their ideal positions such that the IrIr distance has increased (2.72₀ Å (Sm) or 2.63₂ Å (Y)). The ir spectra are reported and discussed in connection with the corresponding factor group analysis.     

Field-Induced Magnetic Properties in RCrO4 Oxides (R=Pr, Gd, Tb, Tm, and Yb)

RCrO₄ oxides (R=Pr, Gd, Tb, Tm, and Yb) have been synthesized at 773 K using the corresponding nitrates as precursors. X-ray diffraction data reveal that these samples are single phases and crystallize with the zircon-type structure, showing tetragonal symmetry, space group I4₁/amd. All the compounds are antiferromagnetic and the Néel temperature, which depends on the R³⁺ ion, takes values lower than 30 K. The presence of a canting appears to be responsible for the negative values of the magnetic susceptibility found below the compensation temperature. This uncommon phenomenon is named reversal of magnetization. It is field-dependent, being suppressed at 500 Oe for the TmCrO₄ compound. The highest value of the compensation temperature (24 K) corresponds to the YbCrO₄ oxide. A metamagnetic transition has been observed in all cases at critical fields ranging from 225 Oe (GdCrO₄) to 1600 Oe (YbCrO₄).     

R12Pt7In (R=Ce, Pr, Nd, Gd, Ho)—new derivatives of the Gd3Ga2-type

A new compound Ce₁₂Pt₇In was synthesized and its crystal structure at 300 K has been determined from single crystal X-ray data. It is tetragonal, space group I4/mcm, Z=4, with the lattice parameters: a=12.102(1) Å and c=14.542(2) Å, wR2=0.1102, 842 F² values, 33 variable parameters. The structure of Ce₁₂Pt₇In is a fully ordered ternary derivative of the Gd₃Ga₂-type. Isostructural compounds has been found to form with Pr (a=11.976(1) Å, c=14.478(2) Å), Nd (a=11.901(1) Å, c=14.471(2) Å), Gd (a=11.601(3) Å, c=14.472(4) Å), and Ho (a=11.369(1) Å, c=14.462(2) Å). Magnetic properties of Ce₁₂Pt₇In, Pr₁₂Pt₇In and Nd₁₂Pt₇In were studied down to 1.7 K. All three ternaries order magnetically at low temperatures with complex spin arrangements. The electrical resistivity of Ce₁₂Pt₇In and Nd₁₂Pt₇In is characteristic of rare-earth intermetallics.     

Structural and magnetic study of RFe0.5V0.5O3 (R=Y, Eu, Nd, La) perovskite compounds

B-site disordered RFe_0.5V_0.5O₃ compounds, with R=La, Nd, Eu and Y, have been prepared by solid-state reaction technique and their structures and magnetic properties have been investigated through X-ray powder diffraction, time-of-flight neutron powder diffraction and magnetization measurements at temperatures ranging from 5 to 700 K. The four compounds can be described as distorted perovskites with space group symmetry Pbnm and a⁺b⁻b⁻ tilt system. The studied compounds also show antiferromagnetic ordering with Neel temperatures of 299, 304, 304, and 335 K respectively. The magnetic structures of R=La, Nd and Y compounds were determined from the neutron powder diffraction as G_z with observed magnetic moments of 2.55, 2.54 and 2.69μ_B at 30, 40 and 40 K, respectively.     

Oxygen permeability, thermal expansion and mixed conductivity of GdxCe0.8−xPr0.2O2−δ, x=0, 0.15, 0.2

The non-linear thermal expansion behaviour observed in Ce_1−yPr_yO_2−δ materials can be substantially controlled by Gd substitution. Coulometric titration shows that the charge compensation mechanism changes with increasing x, in the system Gd_xCe_0.8−xPr_0.2O_2−δ. For x=0.15, charge compensation is by vacancy formation and destabilises the presence of Pr⁴⁺. At x=0.2, further Gd substitution is charge compensated by additionally raising the oxidation state of Pr rather than solely the creation of further oxygen ion vacancies. Oxygen concentration cell e.m.f. measurements in an oxygen/air potential gradient show that increasing Gd content decreases ionic and electronic conductivities. Ion transference numbers measured under these conditions show a positive temperature dependence, with typical values t_o=0.90,0.98 and 0.80 for x=0,0.15 and 0.2, respectively, at 950 °C. These observations are discussed in terms of defect association. Oxygen permeation fluxes are limited by both bulk ambipolar conductivity and surface exchange. However, the composition dependent trends in permeability are shown to be dominated by ambipolar conductivities, and limited by the level of electronic conductivity. At the highest temperatures, oxygen permeability of composition x=0.2 approaches that of composition x=0, Ce_0.8Pr_0.2O_2−δ, with specific oxygen permeability values approximately 2×10⁻⁹ mol s⁻¹ cm⁻¹ at 950 °C, but offering much better thermal expansion properties.