Absorption spectra of Bi3+ and Fe3+ in Y3Ga5O12

The absorption spectra of Y₃Ga₅O₁₂:(Fe³⁺), Y₃Ga₅O₁₂:(Bi³⁺) and Y₃Ga₅O₁₂:(Bi³⁺, Fe³⁺) are presented to 40,000 cm^-1. Assignments are discussed and the transitions analysed in terms of their involvement in the large Faraday rotation observed in bismuth substituted iron garnets.     

A tin-119 Mössbaer spectroscopic study of tin-doped niobium titanium phosphate

¹¹⁹Sn Mössbauer spectroscopy shows that the reaction of metallic tin with niobium titanium phosphate, NbTiP₃O₁₂, results in the accommodation of Sn²⁺ in two types of sites within channels in the NbTiP₃O₁₂ structure. The Sn²⁺ absorptions are characterised by highly positive chemical isomer shifts which decrease as increasing concentrations of Sn²⁺ are incorporated within the NbTiP₃O₁₂ structure. At very high tin concentrations the Mössbauer spectra show the presence of some unreacted elemental tin. The¹¹⁹Sn Mössbauer data are endorsed by X-ray powder diffraction data and are discussed in terms of the incorporation of highly ionic Sn²⁺ species.     

Eu2+, Cr3+共掺杂的MAl12O19 (M=Ca, Sr, Ba) 的发光性质及能量传递

三基色荧光粉中, 红色荧光粉性能较差, 为获得性能优良的红色荧光粉, 本文采用高温固相法合成了Eu²⁺, Cr³⁺单掺杂及共掺杂的碱土金属多铝酸盐MAl₁₂O₁₉ (M =Ca, Sr, Ba) 发光体. 实验表明, 在以上三种基质中均存在Eu²⁺→Cr³⁺的能量传递, 利用能量传递可以有效将Eu²⁺的蓝光或绿光转换为红光. 三种碱土金属多铝酸盐基质的晶体结构相似,但Eu²⁺, Cr³⁺发光受晶体场影响,导致在不同的基质中Eu²⁺, Cr³⁺间能量传递效率不同.通过光谱分析及能量传递效率计算发现, 相同掺杂浓度下,CaAl₁₂O₁₉中Eu²⁺→Cr³⁺的能量传递效率最高,SrAl₁₂O₁₉次之, BaAl₁₂O₁₉最低.红光转换率在CaAl₁₂O₁₉中最高.     

Synthesis and electrical properties of new perovskite-like <Emphasis Type="Italic">A</Emphasis>Mn<Subscript>3</Subscript>V<Subscript>4</Subscript>O<Subscript>12</Subscript> (A = Ca,Ce, and Sm) compounds

AMn₃V₄O₁₂ (A = Ca, Ce, and Sm) compounds with a perovskite structure are synthesized at high pressures and temperatures. The crystalline structure of these compounds (space group \(Im\bar 3\)Z = 2) is determined via X-ray analysis. If ions in the A sublattice are changed in the order Ca²⁺–Sm³⁺–Ce³⁺, the valence is redistributed from Ca²⁺Mn₃²⁺V₄⁴⁺O₁₂ to Sm³⁺Mn₃²⁺V₄^3.75+O₁₂, and to Ce³⁺Mn₃²⁺V₄^3.75+O₁₂. The temperature dependences of the electrical resistivity are studied.     

Magnetic and transport properties of double distorted perovskites CaCuMn6O12 and CaCu2Mn5O12

Magnetic and transport properties of double distorted perovskites CaCuMn₆O₁₂ and CaCu₂Mn₅O₁₂ are studied in a range 2–300 K. The leading role in magnetism of these compounds belongs to antiferromagnetic exchange interaction of Cu²⁺ in square coordination with Mn³⁺/Mn⁴⁺ in octahedral coordination. The values of saturation magnetization indicate that Mn³⁺ ions in square coordination are coupled ferromagnetically with Mn³⁺/Mn⁴⁺ in octahedral coordination. The colossal magnetoresistance in the pellet samples is due assumingly to intergranular spin-polarized tunneling of current carriers.     

High field Mössbauer effect study of LaFe12O19

Mössbauer effect measurements on ⁵⁷Fe in LaFe₁₂O₁₉ at room temperature and at 4.2 K in an external magnetic field of 10 T confirm the suggestion of Lotgering[2] that the replacement of Ba²⁺ in BaFe₁₂O₁₉ by La³⁺ is accompanied by a valence change of Fe³⁺ to Fe²⁺ in the 2a-sublattice. The corresponding Fe²⁺-subspectrum has been detected. The increased hyperfine fields of the 12k- and 2b-sites in LaFe₁₂O₁₉ are discussed in terms of the different exchange paths between the iron sublattices.     

Reversible photochromic effects in doped single crystals of bismuth germanium (Bi12GeO20) and bismuth silicon oxide (Bi12SiO20)

Absorption of Bi₁₂GeO₂₀ and Bi₁₂SiO₂₀ single crystals doped with Mn and Cr were investigated before and after illumination with visible light. Pronounced photochromic effects were found. The effects are explained in terms of light induced charge transfer Mn⁴⁺→Mn⁵⁺ and Cr³⁺→Cr²⁺.     

Luminescent properties and energy transfer of Y3Al5O12:Ce3+, Ln3+ (Ln=Tb,Pr) prepared by polymer-assisted sol–gel method

Y₃Al₅O₁₂:Ce³⁺, Pr³⁺ and Y₃Al₅O₁₂:Ce³⁺, Tb³⁺ nano-particles have been synthesized by polymer-assisted sol–gel method. Crystal structure, luminescent properties and energy transfer of the phosphors are analyzed. XRD study of polycrystalline powders shows that all the samples are of YAG phase without impurity. Photoluminescence (PL) emission and excitation spectra illustrate that in YAG:Ce, Pr phosphors, energy transfer occurs mutually between Ce³⁺ and Pr³⁺, while in YAG:Ce, Tb systems, only one-way path energy transfer of Tb³⁺→Ce³⁺ is observed.     

Preparation and characteristics of Li4Ti5O12 with various dopants as anode electrode for hybrid supercapacitor

Spinel-Li₄Ti₅O₁₂ is successfully synthesized by a solid phase synthesis. The Li₄Ti₅O₁₂ powders with various dopants (Al³⁺, Cr³⁺, Mg²⁺) synthesized at 800 °C are in accordance with the Li₄Ti₅O₁₂ cubic spinel phase structure. The dopants are inserted into the lattice structure of Li₄Ti₅O₁₂ without causing any changes in structural characteristics. In order to study the effect on various dopants, the hybrid supercapacitor is prepared by using un-doped Li₄Ti₅O₁₂ and doped Li₄Ti₅O₁₂ in this work. The electrochemical performance of the hybrid supercapacitor is characterized by impedance spectroscopy and cycle performance. The results show Cr³⁺ and Mg²⁺ dopants enhance the conductivity of Li₄Ti₅O₁₂. Also, Al³⁺ substitution improves the reversible capacity and cycling stability of Li₄Ti₅O₁₂. It is found that effect of dopant on the electrochemical performance of Li₄Ti₅O₁₂ as electrode material for hybrid supercapacitor where the EDLC and the Li ion secondary battery coexist in one cell system.     

Mössbauer effect in LaFe12O19

Mössbauer spectra of ⁵⁷Fe in LaFe₁₂O₁₉ show that the substitution of La³⁺ for Ba²⁺ or Sr²⁺ in XFe₁₂O₁₉ is associated with a valency change of Fe³⁺ to Fe²⁺ at the 2a or 4f₂ site. Temperature dependences of the hyperfine fields at the various sublattices are given.     

Y3Al5O12∶Ce3+的余辉和热释光特性

高温固相法合成了Ce³⁺掺杂的Y₃Al₅O₁₂ (YAG)样品,研究了样品的结构、光致发光和热释发光性质. X射线衍射分析结果表明合成样品为YAG纯相,稀土离子的少量掺杂不改变基质YAG的结构. 荧光光谱测试表明在高温空气气氛下Y_2.95Al₅O₁₂ ∶Ce⁴⁺_0.05制备过程中存在Ce⁴⁺关键词： 长余辉 高温热释光 缺陷     

Enhanced superhyperfine interaction on Ru3+ in Tm3Al5O12 and on Ru3+ and Yb3+ in Tm3Ga5O12

Measurements of the enhanced superhyperfine interaction linking the electron spin of an impurity EPR ion and the nuclear moments of Van Vleck host lattice ions are reported for Ru³⁺ in Tm₃Al₅O₁₂ and for Ru³⁺ and Yb³⁺ in Tm₃Ga₅O₁₂. The Ru³⁺ results appear to be the first reported where this interaction is large enough to give rise to a well resolved superhyperfine structure. For Yb³⁺ the observed temperature dependent line narrowing evidences the role of Tm spin fluctuations.     

Luminescence of Ce3+ ion in aluminate based phosphors for scintillator

Ce³⁺ activated aluminate based phosphors prepared by combustion synthesis are reported here. The emission of Ce³⁺ ion is observed around 321–354 nm in the ultraviolet region of the spectrum. The intensity of strong photoluminescence emission peak of Ce³⁺ ion increases when Mg is added to CaAl₁₂O₁₉ phosphor. The Ce³⁺ emission in CaAl₁₂O₁₉:Ce,Mg phosphor may be useful for scintillation application.     

Optical spectroscopy of Ca3Sc2Si3O12, Ca3Y2Si3O12 and Ca3Lu2Si3O12 doped with Pr

The silicates Ca₃Sc₂Si₃O₁₂, Ca₃Y₂Si₃O₁₂ and Ca₃Lu₂Si₃O₁₂, both undoped and doped with Pr³⁺ ions, have been synthesized by solid-state reaction at high temperature. The luminescence spectroscopy and the excited state dynamics of the materials have been studied upon VUV and X-ray excitation using synchrotron radiation. All doped samples have shown efficient 5d-4f emission upon direct VUV excitation of 5d levels, but only Ca₃Sc₂Si₃O₁₂:Pr³⁺ shows luminescence upon interband VUV or X-ray excitation. The VUV excited emission spectra of Ca₃Y₂Si₃O₁₂:Pr³⁺ and Ca₃Lu₂Si₃O₁₂:Pr³⁺ show features attributed to emission from two distinct sites accommodating the Pr³⁺ dopant. The decay kinetics of the Pr³⁺ 5d-4f emission in Ca₃Sc₂Si₃O₁₂:Pr³⁺ upon VUV excitation across the band gap are characterized by decay times in the range 25-28 ns with no significant rise after the excitation pulse. They appear to be faster upon X-ray irradiation than for VUV excitation. Weak afterglow components are attributed to defect luminescence.     

Density functional investigation of metal encapsulated X@C12Si8 heterofullerene (X=Li, Na, K, Be, Mg, Ca, Al, Ga)

The stability and the possible application of our recently reported SiC heterofullerenes inspire the investigation of their further stabilization through ion encapsulation. The endohedral complexes X@C₁₂Si₈, where X=Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, Ca²⁺, Al³⁺, and Ga³⁺, are probed at the MPWB1K/6-311G? and B3LYP/6-311G* levels of theory. The optimized geometries show the expanding or contracting capability of C₁₂Si₈ in order to accommodate metal ion guests. The inclusion energies indicate the stability of the complexes compared to the components. Meanwhile, the calculated binding energies show the stabilization of C₁₂Si₈ through the inclusion of Be²⁺, Mg²⁺, Al³⁺, and Ga³⁺. The host-guest interaction that is probed through NBO atomic charges supports the obtained results. This study refers to “metal ion encapsulation” as a strategy for stabilization of SiC heterofullerenes.     

Measurement of spin-alignment of excited12C2+ nuclei in interactions of16O with12C usingγ-decay in flight

Measuring energy spectra of nuclei afterγ-decay of excited states in flight the spin alignment of¹²C₂₊ states has been measured. Inelastic scattering,¹⁶O(¹⁶C,¹²C₂₊)¹⁶O and the reaction¹²C(¹⁶O,¹²C₂₊)¹⁶O leading to¹²C₂₊ (4.43 MeV) state have been studied. Characteristic line shapes of the¹²C₂₊ peak were observed using a Q3D magnetic spectrometer. The magnetic substate (m-states) population has been deduced from the spectra as function of reaction angle. A comparison of the measuredm-state population with reaction models shows that the first reaction is consistent with inelastic scattering although discrepancies remain. Discrepancies are also obtained if the reaction¹²C(¹⁶O,¹²C₂₊)¹⁶O is interpreted using a FRDWBA transfer calculation. At least 1/3 of the cross section can be attributed toα-transfer. A calculation which couples transfer and inelastic scattering channels seems to be necessary.     

XPS study of rare earth dodecaborides: TmB12, YbB12 and LuB12

Single phase TmB₁₂, YbB₁₂ and LuB₁₂ were successfully obtained by the arc-melting and floating zone methods. The XPS measurements of these compounds have indicated that (1) only YbB₁₂ is a valence fluctuating compound with the valency of +2.9 at room temperature, (2) the correlation energy between Yb²⁺ and Yb³⁺ ions is about 6.0 eV, (3) Tm and Lu ions in the dodecaborides are in a trivalent state, and (4) the binding energy of the 4f level in TmB₁₂ and LuB₁₂ is 5.0 and 7.7 eV, respectively.     

Luminescence properties of phosphors based on Tb<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript> (TbAG) terbium-aluminum garnet

The processes of excitation energy transfer in phosphors based on single-crystal Tb₃Al₅O₁₂:Ce (TbAG:Ce) and Tb₃Al₅O₁₂:Ce,Eu (TbAG:Ce,Eu) garnet films have been investigated. These films are considered to be promising materials for screens for X-ray images and luminescence converters of blue LED radiation. The conditions for excitation energy transfer from the matrix (Tb³⁺ cations) to Ce³⁺ and Eu³⁺ ions in TbAG:Ce and TbAG:Ce,Eu phosphors have been analyzed in detail. It is established that a cascade process of excitation energy transfer from Tb³⁺ ions to Ce³⁺ and Eu³⁺ ions and from Ce³⁺ ions to Eu³⁺ ions is implemented in TbAG:Ce,Eu via dipole-dipole interaction and through the Tb³⁺ cation sublattice.     

Iron-57, tin-119, and antimony-121 mössbauer spectroscopic investigations of metal atom incorporation into the oxide NbTiP3O12

Tin-119 and iron-57 Mössbauer spectroscopy show that the incorporation of tin and iron into the white oxide NbTiP₃O₁₂ to form black compounds of composition Sn_0.5NTiP₃O₁₂ and Fe_0.33NbTiP₃O₁₂ involves the accomodation of Sn²⁺ and Fe²⁺ in two types of sites in the NbTiP₃O₁₂ host lattice. The change in colour is associated which charge transfer arising from the transfer of electrons from the incorporated metal to the host lattice and the partial reduction of Nb⁵⁺ to a lower oxidation state.The compound SbTiP₃O₁₂ has been synthesised and shown by antimony-121 Mössbauer spectroscopy to contain Sb⁵⁺. The resistance of the SbTiP₃O₁₂ structure to the incorporation of tin and iron is associated with the reluctance of Sb³⁺ to adopt octahedral coordination.     

Effect of different doped elements on visible light absorption and ultraviolet light emission on Er3+:Y3Al5O12

In this progress report, seven kinds of novel carefully designed and fabricated up-conversion luminescence agents, Er³⁺:Y₃Al₅O₁₂, Er³⁺:Yb_nY_3?nAl₅O₁₂, Er³⁺:Y₃B_aAl_5?aO₁₂, Er³⁺:Y₃Ga_bAl_5?bO₁₂, Er³⁺:Y₃Al₅N_xO_12?x, Er³⁺:Y₃Al₅F_yO_12?y and Er³⁺:Yb_nY_3?nB_aGa_bAl_5?a?bN_xF_yO_12?x?y, are successfully synthesized using sol–gel methods. After that, their corresponding photocatalysts, Er³⁺:Y₃Al₅O₁₂/TiO₂, Er³⁺:Yb_nY_3?nAl₅O₁₂/TiO₂, Er³⁺:Y₃B_aAl_5?aO₁₂/TiO₂, Er³⁺:Y₃Ga_bAl_5?bO₁₂/TiO₂, Er³⁺:Y₃Al₅N_xO_12?x/TiO₂, Er³⁺:Y₃Al₅F_yO_12?y/TiO₂ and Er³⁺:Yb_nY_3?nB_aGa_bAl_5?a?bN_xF_yO_12?x?y/TiO₂, are also prepared by sol–gel coating process. The obtained up-conversion luminescence agents and photocatalysts were characterized by using XRD, XPS, SEM, UV–vis and fluorescence spectrophotometer. Synchronously, several kinds of organic dyes are used to test their photocatalytic degradation using prepared photocatalysts. It indicates that the up-conversion luminescence ability of Er³⁺:Y₃Al₅O₁₂ can be improved obviously through doping of some elements. And then, the photocatalytic activity of TiO₂ is markedly enhanced by modified up-conversion luminescence agents which can transform much visible light into ultraviolet light.