Host Ions Research Articles

Creation of inverse population in the 229Th ground-state doublet by means of a narrowband laser

A new method for obtaining inverse population between quadrupole sublevels of the ground state 5/2+(0.0) and the isomeric state 3/2+(7.6 eV) of the 229Th nucleus in a dielectric crystal with a large band gap by means of an external source of VUV radiation is proposed. The method is based on an efficient depopulation of the upper sublevels of the ground state of 229Th by resonant photons from a narrowband laser or a broader tunable free electron laser. The sublevels of the isomeric state play the role of intermediate states. The proposed scheme of optical pumping (1) results in inverse population of nuclear sublevels without using extremely low temperatures, and (2) shows a new means of creating a gamma-ray laser of optical range at the nuclear transition in 229Th (a) in crystals with isovalent substitution of host ions (e.g. Si4+ ions in the SiO2 crystal replaced by the 229Th4+ ions) and (b) in crystals such as Na2ThF6, where the substitution is not necessary.

On the Location of Host Ca Atoms Responsible for Ferrimagnetism in the Layered Cobaltites YBaCo2O5.5

Recent studies have shown that the addition of Ca as host ion in the layered compounds RBaCo2O5+δ (with R a rare earth or yttrium) produces a dramatic effect on their magnetic properties, as well a...

Growth of Oxide Laser Crystals by Czochralski Method

The growth of series of actual laser crystals belonging to di erent structural types by the Czochralski method is presented. The primary attention is given to single crystalline compounds and their solid solutions with garnet structure (scandium-containing rare-earth garnets with general formula {LnSc}3[ScMe]2Me3O12, Me = Al, Ga) as well as with olivine (forsterite Mg2SiO4) and scheelite structure (double tungstates and molybdates with formula NaLn(TO4)2, where T = Mo or W). The broad bands of luminescence and absorption produced by activator ions in these laser hosts that appear either as a result of structural disorder (garnets, scheelites) or due to the doping by transition metal ions (chromium in forsterite) join together these representatives of di erent structural classes and determine their application in photonics. The paper considers the problems of growing of large crystals with uniform distribution of components and dopants, determination of congruently melting composition, especially in compounds with complex isomorphism. The mutual in uence of components and dopants, redistribution of ions along crystallographically non-equivalent sites in the structure, alteration of valency of transition metal ions accompanied with the change of their segregation coe cients under variation of redox conditions is discussed.

Infrared spectroscopic study of Rb2M(XO4)2·6H2O (M = Mg, Co, Ni, Cu, Zn; X = S, Se) and of [formula omitted] guest ions included in rubidium Tutton selenates

The solubility in the three-component systems Rb2SeO4–MSeO4–H2O (M=Mg, Ni, Cu) is studied at 25°C by the method of isothermal decrease of supersaturation. It has been established that double compounds, Rb2M(SeO4)2·6H2O (M=Mg, Ni, Cu), crystallize from the ternary solutions within wide concentration ranges.Infrared spectra of rubidium Tutton compounds, Rb2M(XO4)2·6H2O (X=S, Se; M=Mg, Co, Ni, Cu, Zn) (in the region of 1300–400cm−1) as well as those of SO42- ions included in selenate matrices (up to 15mol%) in the region of the stretching modes ν3 and ν1 are presented and discussed. The matrix-isolated SO42- ions exhibit three bands for ν3 and one band for ν1 in good agreement with the low site symmetry C1 of the SeO42- host ions. The extent of energetic distortion of the isomorphously included ions as deduced from the values of Δν3 (site group splitting) and Δν3/νc (where νc is the centro-frequency value of the asymmetric stretches) is discussed. The comparison of the vibrational behavior of the matrix-isolated SO42- ions (about 2mol%) in different Tutton selenate matrices show that the distortions of the sulfate guest ions increase on going from potassium selenates to ammonium ones. The stronger distortion of the SO42- guest ions in ammonium compounds as compared to that of the same ions included in the potassium and rubidium selenates is due to the formation of hydrogen bonds between the guest ions and the NH4+ host cations additionally to those with water molecules of the host compound. The matrix-isolated sulfate guest ions are stronger distorted in the case of the Rb2Cu(SeO4)2·6H2O, (NH4)2Cu(SeO4)2·6H2O, (NH4)2Zn(SeO4)2·6H2O, and (NH4)2Ni(SeO4)2·6H2O as compared to those in the respective magnesium, cobalt and nickel selenate matrices is due probably to the formation of stronger hydrogen bonds in the former compounds (strong synergetic effect of the copper, zinc and nickel ions) as well as to the formation of hydrogen bonds between the guest ions and the ammonium host ions. The water librations are also briefly discussed.

Vibrio effector protein, VopQ, forms a lysosomal gated channel that disrupts host ion homeostasis and autophagic flux

Defects in normal autophagic pathways are implicated in numerous human diseases--such as neurodegenerative diseases, cancer, and cardiomyopathy--highlighting the importance of autophagy and its proper regulation. Herein we show that Vibrio parahaemolyticus uses the type III effector VopQ (Vibrio outer protein Q) to alter autophagic flux by manipulating the partitioning of small molecules and ions in the lysosome. This effector binds to the conserved Vo domain of the vacuolar-type H(+)-ATPase and causes deacidification of the lysosomes within minutes of entering the host cell. VopQ forms a gated channel ∼18 Å in diameter that facilitates outward flux of ions across lipid bilayers. The electrostatic interactions of this type 3 secretion system effector with target membranes dictate its preference for host vacuolar-type H(+)-ATPase-containing membranes, indicating that its pore-forming activity is specific and not promiscuous. As seen with other effectors, VopQ is exploiting a eukaryotic mechanism, in this case manipulating lysosomal homeostasis and autophagic flux through transmembrane permeation.

Site‐Selective Functionalization of Periodic Mesoporous Organosilica (PMO) with Macrocyclic Host for Specific and Reversible Recognition of Heavy Metal

A novel kind of macrocyclic-host-functionalized periodic mesoporous organosilica (PMO) with excellent and reversible recognition of Pb(II) was developed. The macrocyclic host molecule cis-dicyclohexano[18]crown-6, with strong affinity to Pb(II), was carefully modified as a bridged precursor to build the PMO material. To break down the limit of the functionalization degree for PMOs incorporated with large-sized moieties, a site-selective post-functionalization method was proposed to further decorate the external surface of the PMO material. The selective recognition ability of the upgraded PMO material towards Pb(II) was remarkably enhanced without destroying the mesoporous ordering. Solid-state (13)C and (29)Si NMR spectroscopy, X-ray photoelectron spectroscopy (XPS), XRD, TEM, and nitrogen adsorption-desorption isotherm measurements were utilized for a full characterization of the structure, micromorphology, and surface properties. Reversible binding of Pb(II) was realized in the binding-elution cycle experiments. The mechanism of the supramolecular interaction between the macrocyclic host and metal ion was discussed. The synthetic strategy can be considered a general way to optimize the properties of PMOs as binding materials for practical use while preserving the mesostructure.

Thermally induced ionization of 5d1 state of Ce3+ ion in Gd3Ga3Al2O12 host

We studied the processes occurring in the 5d1 excited state of Ce3+ in Gd3Ga3Al2O12 (GGAG) host. Energy transfer from Gd3+ to Ce3+ was evidenced by photoluminescence excitation spectra of Ce3+ emission. We measured temperature dependences of prompt nanosecond decays and millisecond delayed recombination decays of Ce3+ in GGAG host. The decrease of nanosecond decay times above approximately 200K is due to thermally induced ionization of the 5d1 excited state of Ce3+. Thermal stimulated luminescence glow curve measurements after X-ray or UV (within 4f–5d1 absorption of Ce3+) irradiation at RT provide another support for the ionization effect around this temperature.

Effect of isovalent ion substitution on electrical and dielectric properties of LaCrO3

In the present investigation, the effect of isovalent doping on the electrical and the dielectric properties of the system, La1−xGdxCrO3 was studied. A few compositions of Gd doped lanthanum chromite, La1−xGdxCrO3 (x = 0.00, 0.01, 0.05, 0.10, 0.15 and 0.20) were synthesised via auto-combustion route. The XRD patterns of all the compositions showed single phase formation having crystal structure similar to that of undoped LaCrO3. The Rietveld refinement of the XRD data of all the compositions indicated orthorhombic structure with space group Pnma at room temperature. The SEM micrographs revealed spherical, oval and irregular morphologies of all compositions having low porosity. The FTIR spectra of the investigated compositions showed various structural modes of vibrations. Real part of electrical conductivity exhibited frequency independent behaviour in the frequency range 20 Hz–1 MHz and in the temperature range 40–400 °C. The DC conductivity of the system was found to show Arrhenius behaviour up to 300 °C. The DC conductivity increased with x up to x = 0.01, the trend was reversed in the range 0.01 ⩽ x ⩽ 0.10 and thereafter it again increased with x up to x = 0.20. The temperature and composition dependent conduction mechanism was explained in terms of defects created due to change of concentration of dopant ion and the size difference between the host and dopant ions. The XPS analysis showed that the concentration of Cr6+ sites increased with the increase in Gd concentration, supporting the proposed conduction mechanism. The orientational and the space charge polarisation processes have been attributed to the total dielectric behaviour of the system in the measured frequency and temperature ranges.

Growth and characterization of group-II-alloyed ZnAlO UV-range transparent conductive films prepared by RF magnetron sputtering

ZnAlO films alloyed with various group-II elements (Be, Mg, Ca, Sr) were sputter grown and its effects on the optical and electrical properties of the films were studied. It was observed that addition of Be most efficiently increases the Eg (∼3.8 eV) but results in high resistivity (0.5 Ωcm), while an addition of Mg resulted in a relatively low resistivity (∼7 × 10−4 Ωcm) and moderate increase in Eg (3.7 eV). Other films showed high resistivity (∼1 Ωcm) and relatively low Eg (3.5 eV for ZnSrAlO). It was proposed that the difference in the ionic radii between the alloying elements and the Zn host ion resulted in lattice strain and formation of non-conductive clusters, which would act as the trap centers and scattering centers, reducing the carrier density and the mobility.

On the mechanisms of radiation damage and prospects of their suppression in complex metal oxides

AbstractThe influence of some impurity ions on the increase/decrease in the resistance against irradiation of metal oxides with X‐rays and electrons (low‐dense excitation) or ∼2 GeV Au198 and U238 ions providing a superhigh density of electronic excitations along cylindrical tracks (LET > 30 keV nm−1) has been investigated for fcc MgO single crystals with close ion masses or Lu3Al5O12 and Gd2SiO5 with large unit cells and heavy cations. The radiation effects have been studied using the methods of low‐temperature vacuum ultraviolet spectroscopy (up to 40 eV), cathodoluminescence and thermoactivation spectroscopy. The step‐by‐step annealing of the radiation‐induced absorption, scattering, and luminescence has been performed at the heating of irradiated crystals up to ∼70% of a melting point. Possible experimental manifestations of the temperature‐stable nanosize 3D defects created, according to theoretical predictions, via rearrangement of many host ions at the collapse of discrete solitons (breathers) are detected in Lu3Al5O12 and Gd2SiO5 crystals irradiated with swift heavy ions (fluence of 1012 ions cm−2).

Highly efficient and well-resolved Mn2+ ion emission in MnS/ZnS/CdS quantum dots

We demonstrate a strategy for the growth of Mn2+ ion doped cadmium based II–VI semiconductor quantum dots (QDs) with a designed buffer layer of ZnS (MnS/ZnS/CdS or Mn:CdS QDs), which aims to meet the challenge of obtaining highly efficient and well-resolved Mn2+ ion emission. First, small, high quality MnS cores are obtained by using thiols to replace conventional alkyl amines as capping ligands. Then a buffer layer of ZnS with a tailored thickness is introduced to the QDs before the growth of CdS shells to reduce the size mismatch between the Mn2+ (dopant) and Cd2+ (host) ions. The fabricated MnS/ZnS/CdS core/shell QDs exhibit a high PL QY of up to 68%, which is the highest ever reported for any type of Mn2+ ion doped cadmium based II–VI semiconductor QD. The photoluminescence (PL) of the QDs consists of well-resolved Mn2+ ion emission without any detectable emission from the CdS band edge or surface defects. In addition, our MnS/ZnS/CdS QDs cannot only be made water-soluble, but can also be coated by ligands with short carbon chain lengths, nearly without cost to the PL QY, which could make them strong candidates for practical applications in biology/biomedicine and opto/electronic devices.

Sol-hydrothermal synthesis and optical properties of Eu3+, Tb3+-codoped one-dimensional strontium germanate full color nano-phosphors

Novel near-UV and blue excited Eu(3+), Tb(3+)-codoped one dimensional strontium germanate full-color nano-phosphors have been successfully synthesized by a simple sol-hydrothermal method. The morphologies, internal structures, chemical constitution and optical properties of the resulting samples were characterized using FE-SEM, TEM, HRTEM, EDS, XRD, FTIR, XPS, PL and PLE spectroscopy and luminescence decay curves. The results suggested that the obtained Eu(3+), Tb(3+)-codoped strontium germanate nanowires are single crystal nanowires with a diameter ranging from 10 to 80 nm, average diameter of around 30 nm and the length ranging from tens to hundreds micrometers. The results of PL and PLE spectra indicated that the Eu(3+), Tb(3+)-codoped single crystal strontium germanate nanowires showed an intensive blue, blue-green, green, orange and red or green, orange and red light emission under excitation at 350-380 nm and 485 nm, respectively, which may attributed to the coexistent Eu(3+), Eu(2+) and Tb(3+) ions, and the defects located in the strontium germanate nanowires. A possible mechanism of energy transfer among the host, Eu(3+) and Tb(3+) ions was proposed. White-emission can be realized in a single-phase strontium germanate nanowire host by codoping with Tb(3+) and Eu(3+) ions. The Eu(3+), Tb(3+)-codoped one-dimensional strontium germanate full-color nano-phosphors have superior stability under electron bombardment. Because of their strong PL intensity, good CIE chromaticity and stability, the novel 1D strontium germanate full-color nano-phosphors have potential applications in W-LEDs.

Calcium Selectivity in Liquid Membrane Transport using Anthraquinone Derived Redox Switched Synthetic Ionophores

Selective recognition of alkali and alkaline earth metal ion pairs viz.Li+, Na+, K+, Mg2+ and Ca2+ is of great biological importance. Design and synthesis of ionophores and receptor molecules capable of selectively binding and transporting substrates (neutral and ionic) are based on molecular recognition and used to develop membrane separation systems. This has potential applications in analytical, environmental, and biomimetic chemistry. We have designed and synthesized new series of anthraquinone derived single and double armed ionophores. Supermolecules have been isolated with these synthetic podands as host and metal ions as guest. Interaction has been confirmed by melting point (m.p.), infrared red (IR), and proton nuclear magnetic resonance (1H NMR) spectral analysis and cyclic voltammetric studies. Further, the liquid liquid extraction, bulk liquid membrane (BLM) transport, and supported liquid membrane (SLM) transport studies using polytetrafloroethylene membrane, cellulose nitrate membrane, onion membrane and egg shell membrane, have been done to find out the selectivity of these ionophores for various metal ions. Among the two liquid membrane systems used SLMs is more efficient than BLMs. It is found that double armed and bridged ionophores (A3 to A8) show better extraction ability than single armed ionophores (A1, A2) and ionophore A3 is calcium selective.

Colour centres and nanostructures on the surface of laser crystals

This paper presents a study of structural and radiationinduced colour centres in the bulk and ordered nanostructures on the surface of doped laser crystals: sapphire, yttrium aluminium garnet and strontium titanate. The influence of thermal annealing, ionising radiation and plasma exposure on the spectroscopic properties of high-purity materials and crystals containing Ti, V and Cr impurities is examined. Colour centres resulting from changes in the electronic state of impurities and plasma-induced surface modification of the crystals are studied by optical, EPR and X-ray spectroscopies,scanning electron microscopy and atomic force microscopy. X-ray line valence shift measurements are used to assess changes in the electronic state of some impurity and host ions in the bulk and on the surface of oxide crystals. Conditions are examined for the formation of one- and two-level arrays of ordered crystallites 10-10 to 10-7 m in size on the surface of crystals doped with irongroup and lanthanoid ions. The spectroscopic properties of the crystals are analysed using ab initio self-consistent field calculations for Men+ : [O2-]k clusters.

Dielectric properties and phase transitions of La2O3- and Sb2O3-doped barium strontium titanate ceramics

The dielectric properties and phase transition characteristics of La2O3- and Sb2O3-doped barium strontium titanate ceramics prepared by solid state route were investigated. The microstructure was identified by X-ray diffraction method and scanning electron microscope was also employed to observe the surface morphologies. It is found that (La, Sb)-codoped barium strontium titanate ceramics exhibit typical perovskite structure and the average grain size decreases dramatically with increasing the content of Sb2O3. Both La3+ ions and Sb3+ ions occupy the A-sites in perovskite lattice. The dielectric constant and dielectric loss of barium strontium titanate based ceramics are obviously influenced by La2O3 as well as Sb2O3 addition content. The tetragonal-cubic phase transition of La2O3 modified barium strontium titanate ceramics is of second order and the Curie temperature shifts to lower value with increasing the La2O3 doping content. The phase transition of (La, Sb)-codoped barium strontium titanate ceramics diffuses and the deviation from Curie-Weiss law becomes more obvious with the increase in Sb2O3 concentration. The temperature corresponding to the dielectric constant maximum of (La, Sb)-codoped barium strontium titanate ceramics decreases with increasing the Sb2O3 content, which is attributed to the replacement of host ions by the Sb3+ ions.

A Theoretical Study on the Structural and Energy Spectral Properties of Ce3+ Ions Doped in Various Fluoride Compounds

Geometry optimization and wave function-based complete-active-space self-consistent field-embedded cluster calculations have been performed for a series of Ce3+-doped fluoride compounds (CaF2, YF3, LaF3, KMgF3, LiYF4, K2YF5, and KY3F10) to investigate local coordination structures, crystal field parameters, and 5d1 energy-level structures of doping Ce3+ ions. The crystal-field parameters of Ce3+ are extracted from the calculated energies and wave functions. The calculated crystal-field parameters and 5d1 energy-level structures show excellent consistency with the experimental results. Our calculations show that the onset of 4f → 5d absorption, which is important in phosphors and scintillators, can be well-predicted. Apart from that, the distortion of local structure due to doping, the wave functions, and the crystal-field parameters of 4f1 and 5d1 states of Ce3+ in the hosts can be obtained. Those can seldom be obtained by fitting empirical crystal-field Hamiltonian to experimental data but are required by some detailed theoretical analysis, such as the calculation of transition intensities and hyperfine splittings. The obtained crystal-field parameters of Ce3+ may also be useful for other lanthanide ions in the same hosts.

Luminescence of Li6Gd(BO3)3 crystals upon ultraviolet and inner-shell excitations

The paper presents the results of the study on luminescence and electronic excitations in Li6Gd(BO3)3 single crystals. The optical and luminescence spectroscopy with a sub-nanosecond time resolution upon selective photoexcitation in the energy range from 3.0 to 650eV was used to investigate in detail the luminescence of both the Gd3+ host ions and Ce3+ impurity ions as well as the processes of energy transfer between them. The intrinsic ultraviolet emission at 3.95–3.97eV due to Pj6→S7/28 transitions in the Gd3+ host ion and the fast luminescence at 2.8–3.0eV due to 5d→4f1 dipole-allowed transitions in the Ce3+ impurity ion were studied upon excitations through the intracenter, charge transfer, band-to-band, and inner-shell transitions. The specificity of the energy transfer upon excitation of photoluminescence in the energy range of absorption of the inner shells of different atoms of the crystal, as well as in the energy region of the giant resonance of 4d–4f transitions was revealed. On the basis of the experimental data, the bandgap Eg=9.3eV, the minimum energy of the 5d→4f1 and charge transfer transitions were determined. The expected positions of the ground states of the 4fn and 4fn−15d levels of trivalent lanthanide ions as well as the 4fn+1 and 4fn5d levels of divalent ions were calculated for all the lanthanide ions in Li6Gd(BO3)3 host crystal.

Sequence Alignment of Viral Channel Proteins with Cellular Ion Channels

Sequence alignment is an important tool for identifying regions of similarities among proteins and for, thus, establishing functional and structural relationships between different proteins. Here, alignments of transmembrane domains (TMDs) of viral channel forming proteins with host ion channels and toxins are evaluated. The following representatives of polytopic viral channel proteins are chosen: (i) p7 of HCV and 2B of Polio virus (two TMDs) and (ii) 3a of SARS-CoV (three TMDs). Using ClustalW2, each of the TMDs of the viral channels is aligned, and the overlap is mapped onto structural models of the host channels and toxins focusing on the pore-lining TMDs. The analysis reveals that p7 and 2B TMDs align with the pore-facing TMD of MscL, and 3a-TMDs align with those of ligand-gated ion channels. Possible implications concerning the mechanism of function of the viral proteins are discussed.

Growth and spectroscopic characterization of Pb2+:CaF2 crystals

CaF2 crystals doped with various concentrations of PbF2 (0.4, 0.5, 1 and 2 mol%) were grown in vacuum, in a shaped graphite furnace using the vertical Bridgman method. The optical absorption spectra reveal the four characteristic UV absorption bands (labeled A, B, C and D) of the Pb2+ ions. As the PbF2 concentration increases, the structure of the bands become clearly visible, that is characteristic for the ns2 ions in various hosts. High intensity emission bands in the near UV spectral region have been observed. The dependence on the Pb2+ concentration of the optical absorption and emission of the Pb2+:CaF2 crystals were not reported before.

Intensity of emission from intracenter 4f-transitions in a-Si:H, ZnO, and GaN films doped with rare-earth ions

It is shown that the intensity of emission from intracenter 4f-transitions in amorphous a-Si:H films and crystalline (GaN, ZnO) films doped with rare-earth ions is governed by the local environment of doping impurity ions. In the case of a-Si:H, a pseudo-octahedron with the C4V point group is present due to nanocrystallites, which provides a local environment for rare-earth ions. In the case of a hexagonal crystal lattice in crystalline GaN and ZnO films, the local symmetry of rare-earth ions introduced into the semiconductor matrix by diffusion, with a pseudo-octahedron with the C4V point group, is formed by stresses due to rare-earth ion-oxygen complexes with a radius exceeding that of host ions incorporated at crystal lattice sites. In contrast to GaN films, ZnO films exhibit, on being doped with Tm, Sm, and Yb, both high-intensity emission in the long-wavelength spectral region, characteristic of intracenter 4f transitions in rare-earth ions, and a substantial increase in intensity in the short-wavelength spectral region (λ = 368–370 nm). GaN films doped with rare-earth ions exhibit in this spectral range only an inhomogeneously broadened emission spectrum due to the presence of an emission band characteristic of donor-acceptor recombination.