Ions In Single Crystals Research Articles

Features of the pulsed cathodoluminescence kinetics of neodymium ion in yttrium-aluminum garnet and yttria

The kinetics of pulsed cathodoluminescence of Nd3+ ions in single crystals, ceramics, and nanopowders of Nd3+ : Y3Al5O12 (Nd3+ : YAG) and Nd3+ : Y2O3 under excitation by a 2 ns electron beam with average electron energies of 130, 150, and 170 keV was studied. In this case, the luminescence of these substances occurs after the termination of the electron beam. In Nd3+ : YAG, there are optical transitions from the 2F25/2 level of the neodymium ion in the ultraviolet and visible regions of the spectrum, as well as from the 4F3/2 level in the near infrared region. In Nd3+ : Y2O3, there are not transitions from the 2F25/2 level of the neodymium ion, but infrared luminescence occurs from the 4F5/2 and 4F3/2 levels. The luminescence kinetics is characterized by rise and decay and it is described by the difference of two exponential functions. It is found that the characteristic luminescence decay times are the lifetimes of the 2F25/2, 4F5/2 and 4F3/2 emissive levels, and the rise time is determined by their pumping in recombination and relaxation processes. The rise mechanisms of pulsed cathodoluminescence are substantially different from the mechanisms of "phosphor ignition", which occur during ionization and excitation of the phosphor by an external source. Keywords: pulsed cathodoluminescence, neodymium ion, yttrium-aluminum garnet, yttria, kinetics, rise time, decay time.

Специфика кинетики импульсной катодолюминесценции иона неодима в иттрий-алюминиевом гранате и оксиде иттрия

The kinetics of pulsed cathodoluminescence of Nd3+ ions in single crystals, ceramics, and nanopowders of Nd3+:Y3Al5O12 (Nd3+:YAG) and Nd3+:Y2O3 under excitation by a 2 ns electron beam with average electron energies of 130, 150, and 170 keV was studied. In this case, the luminescence of these substances occurs after the termination of the electron beam. In Nd3+:YAG, there are optical transitions from the 2F25/2 level of the neodymium ion in the ultraviolet and visible regions of the spectrum, as well as from the 4F3/2 level in the near infrared region. In Nd3+:Y2O3, there are not transitions from the 2F25/2 level of the neodymium ion, but infrared luminescence occurs from the 4F5/2 and 4F3/2 levels. The luminescence kinetics is characterized by rise and decay and it is described by the difference of two exponential functions. It is found that the characteristic luminescence decay times are the lifetimes of the 2F25/2, 4F5/2 and 4F3/2 emissive levels, and the rise time is determined by their pumping in recombination and relaxation processes. The rise mechanisms of pulsed cathodoluminescence are substantially different from the mechanisms of "phosphor ignition", which occur during ionization and excitation of the phosphor by an external source.

The binding of precipitant ions in the tetragonal crystals of hen egg white lysozyme

The bonds between lysozyme molecules and precipitant ions in single crystals grown with chlorides of several metals are analysed on the basis of crystal structure data. Crystals of tetragonal hen egg lysozyme (HEWL) were grown with chlorides of several alkali and transition metals (LiCl, NaCl, KCl, NiCl2 and CuCl2) as precipitants and the three-dimensional structures were determined at 1.35 Å resolution by X-ray diffraction method. The positions of metal and chloride ions attached to the protein were located, divided into three groups and analysed. Some of them, in accordance with the recently proposed and experimentally confirmed crystal growth model, provide connections in protein dimers and octamers that are precursor clusters in the crystallization lysozyme solution. The first group, including Cu+2, Ni+2 and Na+1 cations, binds specifically to the protein molecule. The second group consists of metal and chloride ions bound inside the dimers and octamers. The third group of ions can participate in connections between the octamers that are suggested as building units during the crystal growth. The arrangement of chloride and metal ions associated with lysozyme molecule at all stages of the crystallization solution formation and crystal growth is discussed.Communicated by Ramaswamy H. Sarma

Super-quadratic upconversion luminescence among lanthanide ions.

We explore the arguably most fundamental aspect of energy-transfer upconversion (ETU), namely the dependence of upconversion luminescence from a higher-energy level, following ETU excitation from a metastable lower-energy level, on direct luminescence from that metastable level. We investigate ETU among neighboring Nd3+ ions in single crystals of GdVO4 and LaSc3(BO3)4 with different doping concentrations by measuring, after short-pulse laser excitation with different pump energies, the infrared luminescence decay from the metastable 4F3/2 level and the yellow upconversion luminescence decay from the 4G7/2 level. We observe a highly super-quadratic dependence of upconversion on direct luminescence intensity. We conclude that the commonly assumed quadratic law of ETU, as proposed by Grant's model and frequently employed in rate-equation simulations, is inadequate to the description of ETU processes. Whereas Zubenko's model, which considers a finite migration rate, provides significantly better fits to the experimental luminescence-decay curves, also this model cannot accurately reproduce the measured decay curves, partly because it does not take the non-homogeneous distribution of active ions into account.

Stabilization of Eu2+in KLuS2crystalline host: an EPR and optical study

Electron paramagnetic resonance and luminescence spectroscopies were applied to study the incorporation and charge stability of Eu2+ luminescent ions in single crystals of KLuS2:Eu found in an earlier optical study [Jary et al., Chem. Phys. Lett. 574, 61 (2013)]. The location of Eu2+ in the structure was unambiguously determined and three different centers were identified and described. Two of these centers correspond to substitution of Eu2+ for K+ and Lu3+ ions providing thus effective mechanism for Eu2+ incorporation due to the charge self-compensation in the lattice. The observed luminescence spectra are consistent with the results of electron paramagnetic resonance experiment and can be decomposed accordingly. (© 2014 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Family of paramagnetic centers of Ce3+ ions in yttrium aluminum garnet

The electron paramagnetic resonance (EPR) spectra of Ce3+ ions in single crystals of yttrium aluminum garnet have been investigated. It has been found that, in addition to the usually observed EPR signals of Ce3+ ions located in the regular environment at dodecahedral sites of the crystal lattice, the spectra contain a group of less intense anisotropic lines with g-factors close to the corresponding parameters of Ce3+ ions in the regular environment. It has been concluded that the observed satellite lines belong to the family of Ce3+ ions in the immediate vicinity of which there are permutation defects that lead to a change in the strength and symmetry of the crystal field in the vicinity of the paramagnetic center.

Single-crystal rare earths manganites La1−x−yBixAyMnαO3±β (A = Ba, Pb): Crystal structure, composition, and Mn ions valence state. X-ray diffraction and XPS study

Single crystals of La1−xBixMnαO3±β and La1−x−yBixAyMnαO3±β (A=Ba, Pb) are grown, their crystal and electron structure is studied. Relative Mn3+/Mn4+ abundance in each single crystal is determined via fitting experimental Mn2p-spectra with weighted superposition of theoretical spectra of tri- and quadrivalent Mn, and, for barium-free samples, from energy splitting of the Mn3s-spectra components. Strong heterogeneousness of the crystals both in elemental composition and crystal structure is discovered. It is shown that the heterogeneousness displays itself in various oxygenic environments around Mn atoms which give rise to the appearance of Mn4+ ions. A simple model is proposed that allows understanding the nature of the appearance of Mn4+ ions in single crystals of lanthanum–bismuth manganites.

The influence of high magnetic field on electric-dipole emission spectra of Eu3+ in different single crystals

In this work, the effect of pulsed high magnetic field on the integral intensity of the electric-dipole emission spectrum of Eu3+ in YVO4:Eu3+ and GdVO4:Eu3+ single crystals was studied and the results showed magnetic field induced luminescence suppression in YVO4:Eu3+ and luminescence expansion in GdVO4:Eu3+. The single crystals were prepared by the optical floating zone method. The strong effect of the magnetic field on the splitting and emission of 5D0–7F2 and 5D0–7F4 transitions in Eu3+ was investigated. The integral luminescence intensities of Eu3+ are proportional to the magnetic field at higher than 15 T. For GdVO4:Eu3+, the integral intensity increases with the strengthening of magnetic field, and is completely opposite to that for YVO4:Eu3+. In this study, the dependence of luminescence integral intensity on the magnetic field was proposed to be the result of the structural change induced by high magnetic field which changes the symmetry of Eu3+ ions in single crystals.

Experimental measurements of ranges of swift heavy ions in single crystals by “cross-section” technique

By means of the “cross-section” technique with the use of optical and electron scanning microscopy, the projected ranges of swift heavy ions with an energy of ∼1 MeV/amu and more are measured in dielectric and semiconductor single crystals. Comparisons are made against tabular data and results of computer calculations using the E-DEP and SRIM codes.

EPR and Optical Absorption Studies of VO2+-Doped Diammonium Hexaaqua Magnesium(II) Sulfate

ABSTRACT Electron paramagnetic resonance (EPR) studies of VO2+ impurity ion in single crystals of diammonium hexaaqua magnesium(II) sulfate are carried out at 9.5 GHz (X-band) at room temperature. Different spin-Hamiltonian parameters are determined. VO2+ is expected to enter the lattice substitutionally. Superhyperfine splitting is also observed. An EPR study of a powder sample is done that supports the data obtained from single crystal studies. Optical absorption studies are also performed at room temperature. The crystal field parameter (Dq), tetragonal parameters (Ds and Dt), and various bonding parameters are evaluated to estimate the covalency and nature of bonding of VO2+ with its different ligands.

EPR Study of VO2+ Doped Diammonium Tricadmium Tetrakis (Sulfate) Pentahydrate [(NH4)2Cd3(SO4)4 ∙ 5H2O] Single Crystals

Electron paramagnetic resonance (EPR) studies are carried out on vanadyl (VO2+) ions in diammonium tricadmium tetrakis (sulfate) pentahydrate single crystals at room temperature. The EPR spectra of a single crystal exhibit resonance signals characteristic to VO2+ ions. The analysis of EPR spectra indicates that the VO2+ ions in single crystals show two magnetically inequivalent VO2+ sites in distinct orientations occupying substitutional positions in the lattice and showing very high angular dependence. They form in octahedral coordination with tetragonal compression with C 4v symmetry. The spin Hamiltonian parameters are determined, and these parameters have been used to estimate the bonding coefficients of the VO2+ ion in a diammonium tricadmium tetrakis (sulfate) pentahydrate lattice. The parallel and perpendicular components of axially symmetric g and hyperfine (A) tensors are evaluated and the results are discussed and compared with previous reports.

Sidewall epitaxial piezoresistor process and characterisation for in-plane force sensing applications

A selective epitaxial fabrication method to form piezoresistors on the sidewalls of microfabricated cantilevers for in-plane force sensing applications and their preliminary characterisation results is reported. The piezoresistors were made of a doped silicon epitaxial layer using a selective deposition technique by tailoring the process conditions. Silicon oxide was used as a mask, dichlorosilane (DCS) was used as a source gas in a reduced pressure environment and HCl was used to improve selectivity. The authors found that the deposition rates were dependent on the trench widths. The authors further characterised the current- voltage behaviour, noise and sensitivity of these epitaxial sidewall piezoresistors. A typical cantilever had resistance of 0.6 kV ,1 /f coefficient, a ¼ 8, sensitivity of 1100 V/ N( 880 V/m) and resolution of 9.5 nN integrated over the band 10 Hz - 10 kHz. Its sensitivity and resolution are comparable to single-crystal ion implanted piezoresistors and better than most polysilicon or diffused piezoresistors.

EPR and optical absorption studies on Gd3+ ions in ammonium hydrogen malonate single crystals

X-Band electron paramagnetic resonance (EPR) studies of Gd 3+ ions in ammonium hydrogen malonate single crystals have been done at room temperature. Detailed EPR analysis indicates the presence of four physically equivalent but magnetically inequivalent sites. The zero-field splitting parameters and g factor are determined. The Gd 3+ ion is in 8 S state; its levels are split by the action of the crystalline electric field of monoclinic symmetry. The optical absorption spectra of Gd 3+ ions in single crystals of ammonium hydrogen malonate are also recorded at room temperature. The energy levels of the 4f 7 configuration are calculated and compared with those observed experimentally. The values of E 1 =5854±11, E 2 =31±0.36, E 3 =592±3.3 and ζ 4f =1595±25 cm −1 are found to give the best over-all agreement between experimentally observed and calculated levels.

Crystal-field energy level analysis forNd3+ ions at thelow symmetry C1 site in [Nd(hfa)4(H2O)](N(C2H5)4) single crystals

Optical absorption measurements ofNd3+ ions in singlecrystals of [Nd(hfa)4(H2O)](N(C2H5)4) (hfa = hexafluoroacetyloacetonate), denoted Nd(hfa) for short, have been carried out at 4.2 and 298 K.This compound crystallizes in the monoclinic system (space groupP 21/n). Each Nd ion is coordinated to eight oxygen atoms that originate from thehexafluoroacetylacetonate ligands and one oxygen atom from the water molecule.A total of 85 experimental crystal-field (CF) energy levels arising from theNd3+ (4f3) electronic configuration were identified in the optical spectra and assigned. A three-stepCF analysis was carried out in terms of a parametric Hamiltonian for the actualC1 symmetryat the Nd3+ ion sites. In the first step, a total of 27 CF parameters (CFPs) in the Wybourne notationBkq, admissible by group theory, were determined in a preliminary fitting constrained by theangular overlap model predictions. The resulting CFP set was reduced to 24 specificindependent CFPs using appropriate standardization transformations. Optimizations of thesecond-rank CFPs and extended scanning of the parameter space were employed in the secondstep to improve reliability of the CFP sets, which is rather a difficult task in the case of nosite symmetry. Finally, seven free-ion parameters and 24 CFPs were freely varied, yieldingan rms deviation between the calculated energy levels and the 85 observed ones of11.1 cm−1. Our approach also allows prediction of the energy levels ofNd3+ ions that are hidden in the spectral range overlapping with strong ligand absorption, whichis essential for understanding the inter-ionic energy transfer. The orientation of the axissystem associated with the fitted CF parameters w.r.t. the crystallographic axes isestablished. The procedure adopted in our calculations may be considered as a generalframework for analysis of CF levels of lanthanide ions at low (triclinic) symmetry sites.

An EPR study of Er3+ impurities in RbTiOPO4 single crystals

An electron paramagnetic resonance (EPR) study of Er3+ ions in single crystals of RbTiOPO4 (RTP) is presented. The EPR spectra show the existence of six different Er3+ centres. The g-matrix has been determined for these centres from the analysis of the angular dependences of the spectrum in three planes of the crystal. The study supports that erbium can enter the Rb+ and Ti4+ low-symmetry sites of RTP. This conclusion differs from those for KTP:Er3+ and RTP codoped with Nb and Er. The different occupancies found for Er in these various crystals is suggested to be due to the differences in Er concentration.

Analysis of hyperfine structure of Rare‐Earth Ions in Single Crystals by Electron Paramagnetic Resonance Spectroscopy

Electron paramagnetic spectroscopy of rare‐earth ions in single crystals is an interesting tool to analyze the hyperfine structure of the ground state of the rare‐earth. This can be useful for coherent spectroscopy and quantum information applications where the hyperfine structure of the electronic levels is used. Moreover, in some cases, the electron paramagnetic resonance hyperfine structure of interacting rare‐earth ions allows us to retrieve the isotropic exchange interaction between the two interacting ions. We illustrate these points with the hyperfine structure of Yb3+ ions in vanadate crystals, the hyperfine structure of Er3+ ions in Y2SiO5, and the hyperfine structure of Yb3+ pairs in CsCdBr3.

Energy transfer and cooperative processes in Yb 3+-doped cubic sesquioxide laser ceramics and crystals

A comparative discussion of the spectroscopic and energy transfer properties of the Yb 3+ ion in single crystals and transparent ceramics of cubic sesquioxide materials is presented. The spectroscopic studies of Yb 3+ and of other rare earth ions co-doped with Yb 3+ in transparent ceramic sesquioxides with ceramic grains of tens of microns show that the variety of structural centres of the doping ions and the distribution of the doping ions in these centres as well as the crystal field interaction, the electron–phonon interaction and the energy transfer processes in these materials are similar to those from single crystals. The cooperative absorption and emission of Yb 3+ in transparent Sc 2O 3 ceramics, facilitated by the very suitable packing of the cationic sites, corresponds to the trends observed in the crystalline materials, showing that no obvious agglomeration of Yb 3+ in these ceramics takes place.

Er3+ impuritiesin KTiOPO4 studied by electron paramagnetic resonance

An electron paramagnetic resonance (EPR) study ofEr3+ ions in singlecrystals of KTiOPO4 (KTP) is presented. The EPR spectra show the existence of eight differentEr3+ centres.The g-matrix has been determined for all eight centres from the analysis of theangular dependences of the spectrum in three planes of the crystal. This studyprovides strong evidence about incorporation of erbium in the low-symmetryK+ sites of KTP. Possible reasons for the appearance of such a large number ofEr3+ centres are discussed.

Hole burning study of Tm 3+:YAG hyperfine structure for quantum storage applications

Quantum storage, which aims at transferring photon quantum states into matter, can be obtained by using an ensemble of atoms whose levels form a three level Λ system. In these systems, two optical transitions couple two levels to a third one. This quantum storage scheme could be obtained with rare-earth ions in single crystals, since their optical and ground-state hyperfine transitions can exhibit long coherence lifetimes and their hyperfine structures could be used to build a three level Λ system. Tm 3+ ions in Y 3Al 5O 12 are especially interesting since the 3H 6– 3H 4 transition can be driven by ultra-stable laser diodes. However, the selection rules on the nuclear spin projection can forbid the simultaneous coupling of two levels to a third one. In this paper, the hyperfine structure of Tm 3+ is investigated by hole burning spectroscopy under a magnetic field and compared to theoretical calculations based on crystal field calculations. The experimental results are found to be in good agreement with theory and show that some magnetic field orientations are able to relax the selection rules on the nuclear spin projection.

The D2h Distortion around the Cu2+ Center in Cu0.5Zr2(PO4)3 Single Crystals

A formula for the calculation of the three g factors of 3d9 ions in an orthorhombic field D2h has been derived. Using it to investigate the EPR g factors of the Cu2+ ions in single crystals of Cu0.5Zr2(PO4)3, the variation of the g factors on changing the angle α between the x- and y-axis has been explained. According to that, it can be confirmed that the angle α of the D2h distortion is about 62.6°. PACS: 71.70C; 76.30F