RbCl Crystals Research Articles

Electronic structure and optical spectra of Au− ions in RbCl

Ab initio wavefunction based quantum chemical calculations on the electronic structure and optical spectra of Au− ions in RbCl crystals are reported in this work. ns2 impurities in alkali halides are prototypical phosphor materials and have been extensively studied. In particular, RbCl:Au− has been recently studied experimentally, but some points of the interpretation of the spectra are still controversial. Our calculations, that include all the major interactions present in the system, show very good agreement with the experimental findings. The calculations show that the levels belonging to the 5d96s26p electron configuration lie relatively low in energy, and extensive mixing with some of the 6s6p levels is found. Large mixing of singlet and triplet states via spin-orbit coupling is found for most of the calculated levels. Due to this, band C in the absorption spectrum is found to consist of two transitions, to the 2 T1u and 3 T1u electronic levels, described as configurational mixtures of 6s6p-1P1 and 5d96s26p levels. Transitions to 5d96s26p levels are found to be responsible for the D absorption bands of the material. On the other hand, emission band C′ is assigned to a transition from the 1 A2u (5d96s26p) electronic level to the ground level, a transition that is electric dipole forbidden. This level lies just below the levels responsible of the C absorption (around 200 cm−1). These findings can justify the complex behavior of this C′ emission.

Formation of solid RbCl from aqueous solutions through membrane crystallization

Rubidium (Rb) is a very precious alkali metal with a high economic value. Of the rubidium compounds, RbCl is probably the most widely used. In the present work, RbCl crystals were obtained by vacuum membrane crystallization (V-MCr). Two different membranes were utilized: (i) one in polypropylene (PP) and (ii) one in poly(vinylidene fluoride)(PVDF). The membranes differ in material but have equal pore and porosity, and the experiments with the two membranes were conducted at the same temperature, vacuum pressure and flow rate values. While RbCl crystals were not obtained with the PVDF membrane due to wetting, good crystals were achieved from experiments with the PP membrane, with dispersion of crystal size distribution around of the average size of just 33.6 %. Another important result is that, in addition to the operating conditions, the membrane material is decisive for the success or failure of the membrane crystallization operation.

The influences of parabolic potential and magnetism on strongly coupled polaron characteristics within asymmetric Gaussian quantum wells

In this research, the effects of magnetism and parabolic potential on strongly coupled polaron characteristics within asymmetric Gaussian quantum wells (AGQWs) were investigated. To do so, the following six parameters were studied, temperature, AGQW barrier height, Gaussian confinement potential (GCP) width, confinement strengths along the directions of [Formula: see text] and [Formula: see text], as well as magnetic field cyclotron frequency. The relationships among frequency oscillation, AGQW parameters and polaron ground state energy in RbCl crystal were studied based on linear combination operator and Lee–Low–Pines unitary transformation. It was concluded that ground state energy absolute value was decreased by increasing GCP width and temperature, and increased with the increase of confinement strength along [Formula: see text] and [Formula: see text] directions, cyclotron frequency of magnetic field and barrier height of AGQW. It was also found that vibrational frequency was increased by enhancing confinement strengths along the directions of [Formula: see text] and [Formula: see text], magnetic field cyclotron frequencies, barrier height AGQW and temperature and decreased with the increase of GCP width.

Electronic states and relaxation dynamics of Au─ centers in RbCl crystals

We investigated the electronic states and nonradiative transitions among the relaxed excited states of Au− centers in RbCl crystals. To this end, we measured the temperature dependences of the luminescence intensities and decay time constants of the A′, B′, and C′ luminescence bands, which are attributed to the radiative transitions from the relaxed excited states of Au− centers. The intensities and decay time constants of these luminescence bands change with temperature, through the thermally activated nonradiative transitions among the relaxed excited states. The temperature dependences of the luminescence intensities and decay time constants were analyzed utilizing rate equations, except the decay time constant of the C′ luminescence. From the best fitting results, the activation energies of the relaxed excited states are estimated. The C′ luminescence has a longer decay time constant than that expected from the dipole-allowed transition. The temperature dependence of the decay time of the C’ luminescence is discussed by considering a trapped level.

Sputtering of LiF and other halide crystals in the electronic energy loss regime

Sputtering experiments were performed by irradiating LiF, NaCl, and RbCl crystals with various swift heavy ions like S, Ni, I, Au with energies between 60 and 210 MeV, C60 clusters between 12 and 30 MeV or Pb ions between 730 and 6040 MeV. Sputtered species are collected on arc-shaped catchers and subsequently analyzed by elastic recoil detection analysis or Rutherford backscattering analysis. The study focuses on angular distributions and total yields for LiF and covers a broad range of experimental parameters including cleaved or rough sample surfaces, ion fluence, beam incident angles, and different ion velocities leading to electronic energy loss (Se) values from 5 to 45 keV/nm. In most cases, the angular distribution has two components, a jet-like peak perpendicular to the surface sample superimposed on a broad isotropic cosine distribution whatever is the beam incident angle. The observation of the jet depends mainly on the surface flatness and angle of ion incidence. However, the jet does not appear clearly when irradiated with C60 cluster. The sputtering yield is stoichiometric and characterized by huge total yields of up to a few 105 atoms per incident ion. The yield follows a power law as function of electronic energy loss, Y follows an exponential law with Sen with n ~ 4. While the azimuthal symmetry for sputtering is observed at low ion velocity (~1 MeV/u), it seems to be lost at high velocity (>4 MeV/u). The data provide a comprehensive overview how the angular distribution and the total sputtering yield scale with the energy loss, beam incidence angle and ion velocity. Complementary experiments have been done with NaCl and RbCl targets confirming the observation made for LiF.

Effect of hydrogen-like impurity on a qubit in quantum pseudodot at finite temperature

Influences of temperature on the qubit's properties in a quantum pseudodot (QPD) are studied by using the variational method of Pekar type (VMPT) and quantum statistics theory (QST). The formation of qubit requires two special conditions: One is the strong-coupling between the electron and the bulk longitudinal optical (LO) phonon, and the other is the hydrogen-like impurity (HLI) locating at the center of the QPD. So, we choose strong-coupling RbCl crystal as an example and calculate the electron probability density (EPD) and the oscillating period (OP) of the QPD qubit changing with the temperature and the Coulombic impurity potential (CIP).

The properties of an asymmetric Gaussian potential quantum well qubit in RbCl crystal**Project supported by the National Natural Science Foundation of China (No. 11464033) and the Mongolia University for Nationalities Fund (No.NMDYB1445).

With the circumstance of the electron strongly coupled to LO-phonon and using the variational method of Pekar type (VMPT), we study the eigenenergies and the eigenfunctions (EE) of the ground and the first excited states (GFES) in a RbCl crystal asymmetric Gaussian potential quantum well (AGPQW). It concludes: (i) Two-energy-level of the AGPQW may be seen as a qubit. (ii) When the electron located in the superposition state of the two-energy-level system, the time evolution and the coordinate changes of the electron probability density oscillated periodically in the AGPQW with every certain period fs. (iii) Due to the confinement that is a two dimensional x−y plane symmetric structure in the AGPQW and the asymmetrical Gaussian potential (AGP) in the AGPQW growth direction, the electron probability density presents only one peak configuration located in the coordinate of z > 0, whereas it is zero in the range of z < 0. (iv) The oscillatory period is a decreasing function of the AGPQW height and the polaron radius. (v) The oscillating period is a decreasing one in the confinement potential R < 0.24 nm, whereas it is an increasing one in the confinement potential R > 0.24 nm and it takes a minimum value in R = 0.24 nm.

The Properties of the Polaron in Semiconductor Quantum Dots Induced by Influence of Rashba Spin-Orbit Interaction

The properties of the effective mass of polaron in semiconductor quantum dots by influence of Rashba spin-orbit (SO) interaction are studied. The relations of the strength of confinement ω0, the interaction energy and the effective mass of the polaron in the electron-LO phonon strong coupling region in a parabolic quantum dot on the vibration frequency is derived by using improved liner combination operator method. Numerical calculations for RbCl crystal are performed and the results show that the Rashba SO interaction makes the ground state energy and the effective mass of polaron split into two branches; the ground splitting energy and the effective mass will increase with the vibration frequency increasing. Whereas the interaction energy is sharply increased until the confinement strength reaches a certain value, then it will sharply decrease.

EFFECTIVE MASS OF STRONG-COUPLED BOUND POLARON IN AN ASYMMETRIC QUANTUM DOT INDUCED WITH RASHBA EFFECT

In this paper, on the basis of Huybrechs' strong-coupled polaron model, the Tokuda-modified linear-combination operator method and the unitary transformation method are used to study the properties of the strong-coupled bound polaron considering the influence of Rashba effect, which is brought by the spin-orbit (SO) interaction, in an asymmetric quantum dot (QD). The expression for the effective mass of the polaron as functions of the transverse and longitudinal bound strengths, velocity, vibration frequency, and the bound potential has been derived. After a simple numerical calculation on the RbCl crystal, we found that the total effective mass of the bound polaron is composed of three parts. The interaction between the orbit and the spin with different directions has different effects on the effective mass of the bound polaron.

Ultrviolet absorption spectra of Eu &lt;sup&gt;+2&lt;/sup&gt; ions in RbCl and RbI single crystals

Ultrviolet absorption spectra of Eu &lt;sup&gt;+2&lt;/sup&gt; ions in RbCl and RbI single crystals

THE EFFECTIVE MASS OF STRONG-COUPLING MAGNETOPOLARON IN QUANTUM DOT

The properties of the strong-coupling magnetopolaron in a parabolic quantum dot are studied for the first time using an improved linear combination operator method. The relation between the vibration frequency, the interaction energy and the effective mass of the strong-coupling magnetopolaron in a parabolic quantum dot with the magnetic field, the confinement strength and the electron-phonon coupling strength were derived. Numerical calculations for the RbCl crystal, for example, are performed and the results show that the vibration frequency, the effective mass and the interaction energy of the strong-coupling magnetopolaron in a parabolic quantum dot will increase quickly with decreasing effective confinement length of the quantum dot. Those attributed to interesting quantum size effects will appear.

Strain rate sensitivity of flow stress under superimposition of ultrasonic oscillatory stress during plastic deformation of RbCl doped with Br − or I −

Strain rate cycling tests were carried out under superimposition of ultrasonic oscillation during plastic deformation of RbCl single crystals doped with Br − or I −. The relation between the strain rate sensitivity λ ( = d τ / d ln ⁡ ε ˙ ) of flow stress and stress decrement Δ τ due to application of oscillation has a stair-like shape and is divided into three regions, two plateaus at low and high Δ τ and the decreasing λ region between them. The stress decrement τ p at the first bending point is considered to be the effective stress due to an impurity and the value of λ p, the difference in λ between the first and second plateau regions is also a part of λ due to an impurity. Values of τ p and λ p were measured from 77 K to room temperature. Assuming the Cottrell–Bilby relation for RbCl crystals doped with Br − or I −. The interaction energies between dislocation and Br − or I − were determined to be 0.50 or 0.58 eV in RbCl, respectively.

Alkali Metal NMR Chemical Shielding as a Probe of Local Structure: An Experimental and Theoretical Study of Rb+ in Halide Lattices

When Rb+ is incorporated into different cubic halide lattices at very low concentrations, the 87Rb NMR chemical shift becomes more shielded by as much as 282 ppm when the cation is changed from Na+ to Cs+. Similarly, in mixed crystals of KCl and RbCl, the average resonance frequency shifts with the degree of incorporation. The 87Rb chemical shift data for each halide show a near-linear correlation with the average alkali metal−halide interionic distance in the different crystals studied, in good agreement with ab initio calculations which show that indeed the chemical shielding has a strong dependence on the nearest neighbor shell of halide anions and their distance from the Rb+. When the Rb concentration is increased as in KCl/RbCl solid solutions, the 87Rb NMR spectra are influenced by a large distribution of K/Rb configurations in the next-nearest-neighbor shell of 12 cations. While the total shift is still largely dependent on the Rb−Cl distance, shells containing both K and Rb atoms give rise to seco...

Luminescence of OH − impurities in crystals of rubidium halides

Photoluminescence of crystals of RbCl, RbBr, RbI doped with OH − ions was systematically investigated as a function of dopant concentration and temperature. The emission spectra show the occurrence in all three systems of three emission bands due to hydroxyl impurities, whose features are in good agreement with previous findings in potassium halides and partial data on RbCl and RbBr. The luminescence of OH − ions in RbI was identified and characterized for the first time. Emission bands caused by other kinds of oxygen-related centers, such as O 2 − molecular ions and perhaps O 2- ions, were revealed.

Hole-electron mechanism of F-H pair generation in RbCl crystals with impurity electron traps

Production of F, Cl 3 − , Ag0, and Tl0 centers in RbCl:Ag and RbCl:Tl crystals by photons having energies ranging from 5 to 10 eV has been studied at 295 and 180 K. It is shown that creation of near-impurity excitations is accompanied by formation of F centers localized in the vicinity of Ag+ and Tl+ ions. F centers are produced in direct optical generation of self-trapped excitons. In addition to the well-known mechanism of F-H pair production in nonradiative recombination of electrons with self-trapped holes, a hole-electron process has been revealed for the first time to operate in RbCl:Ag having deep electron traps. By this mechanism, F-H pairs appear in the following sequence of stages: thermally stimulated unfreezing of hopping diffusion of self-trapped holes (V K centers), tunneling electron transfer from Ag0 to the approaching V K centers, and subsequent nonradiative decay of triplet self-trapped excitons near Ag+ ions.

Peculiarities of stable Frenkel defect formation in RbCl crystals

Low creation efficiency of stable F–H and α–I pairs in RbCl is determined by the microstructure of H centres (Cl 2 − molecule is not interacting with neighbouring anions). The spectrum of F-centre creation has been measured for RbCl : Tl using synchrotron radiation 6–20 eV. At 295 K the creation efficiency is especially high in the regions 14.5–15.7 and 15.7–17.0 eV where the energy of hot photoelectrons is sufficient for the formation of near-impurity excitations or secondary excitons, respectively. A new mechanism of F–H pair creation has been revealed in RbCl : Ag. The heating of an irradiated crystal up to 210–240 K provides the tunnel recharging of V K and Ag 0 centres with the creation of Frenkel defects.

Metastable one-halide self-trapped excitons in alkali halides

Fast (τ < 2 ns) short-wavelength emissions have been detected overlapping the continuous intraband luminescence on exciting KBr, RbBr, KCl and RbCl crystals by an electron beam. These emissions are attributed to the radiative decay of metastable one-halide self-trapped excitons. The weak 5.8 eV emission can effectively be excited in a KBr crystal in the region of the formation of excitons (6.73-7.3 eV).

Relaxation of excitons in wide-gap CsCl crystals

Optical characteristics of free and self-trapped excitons are investigated in simple cubic CsCl crystals of high purity. The reflection, photoluminescence, cathodoluminescence and X-ray luminescence spectra, as well as the excitation spectra for intrinsic, impurity and near-defect emissions and spectra of the anion Frenkel defect creation by radiation are measured in CsCl crystals at 5-80 K in the spectral region of 2 to 10 eV. A weak emission at 8.3 eV and pi -emission of self-trapped excitons (2.82 eV) are detected in CsCl at 5 K. The energy gap is estimated as Eg=8.4 eV at 5 K. Some peculiarities of the radiative and non-radiative decay of excitons in SC CsCl in comparison with those of FCC KCl and RbCl crystals are discussed.

Diffusion of Cl2Molecules in NaCl and RbCl Crystals Doped with OH-Ions

Diffusion measurements have been made for Cl 2 in NaCl and RbCl crystals doped with OH - ions. Diffusion front was detected by observing the blue coloration with electron irradiation or the yellow fluorescence due to O 2 - ions. The solution of the diffusion equation with a chemical reaction permits the evaluations of diffusion coefficient and Henry's constant of Cl 2 in these crystals. Activation energies of the diffusion are 1.61±0.11 eV with D 0 =5.8×10 -5 m 2 s -1 in NaCl and 1.84±0.24 eV with D 0 =7.1×10 -2 m 2 s -1 in RbCl. These results are compared with theoretical results by Diller. Temperature dependence of the Henry's constant indicates that dissolution of Cl 2 molecules at the surface is the exothermic reaction.

Investigations of Defect Centres in Alkali Halides Doped with Trivalent Cations. Part 1: Bismuth in NaCl, KCl and RbCl Crystals

A correlated set of experiments was performed with a view to study the effect of trivalent bismuth upon some properties of NaCl, KCI and RbCI crystals. For NaCI the effect of BiO+ ions was also investigated. It was stated that: 1. The hydrolytic properties of bismuth are responsible for the formation of BiO+ centres also in crystals doped with BP+ ions. 2. During all experiments performed, the dopant remains in the form of trivalent cations. 3. Optical absorption spectra of bismuth are similar to those characteristic of other heavy metal ions with the s 2 electronic configuration. 4. The charge excess of BP+ ions is compensated by cation vacancies whereas for BiO+ ions the preferential bonding between Iii and O 2— serves for the charge compensation.