Intraionic Transitions Research Articles

A theoretical investigation on the magneto-optical effect of CeF 3 and NdF 3

In this paper the calculations of magneto-optical Verdet constants and susceptibilities of CeF 3 and NdF 3 compounds in the temperature range 40–300 K are presented. It is found that the magneto-optical effects of these compounds are mainly caused by the intra-ionic electric dipole transitions between the 4f and 5d energy levels split by the crystal and magnetic fields. The mixed-valent behavior of the Ce ions in CeF 3 has an important effect on the Faraday rotation and susceptibility. The theoretical results are in agreement with experiments.

Magnetic circular dichroism in YBa 2Cu 3O x thin films

Magnetic circular dichroism (MCD) in superconducting and insulating YBa 2Cu 3O x thin films is studied. The MCD spectra in superconducting samples exhibit a linearly field dependent structure at 4–5 eV. The field and temperature dependences, the latter seeming to obey the Curie law, suggest that this structure is associated with the intraionic 3d-4p transitions of localized Cu ions at the Cu-O chains. These transitions are thought to be the origin of the peak at 4.1 eV observed in insulating ones. A comparison of the spectra of insulating YBa 2Cu 3O x dielectric function studies and this work is also given.

Auger Transitions as Luminescence Killers in lonic Solids

The role of the interionic and intraionic Auger transitions as crossluminescence killers in CsBr crystals is studied by Monte Carlo simulation procedure. It is shown that to undestand the essential features of the crossluminescence excitation spectrum near its threshold it is necessary to suppose for holes in the uppermost cation band the validity of the inequality τr ≫ τp > τa, τr being the time of their radiative relaxation (i.e. the crossluminescence decay time), τp, the time of their relaxation by scattering on phonons, and τa, the time of their intrrionic Auger relaxation, and the strong influence on τp and τa of the spin-orbit splitting of the valence and the cation bands. At higher photon energys, where the inner cation shells are ionized, the crossluminescence is partially killed by multiple Auger ionization of cation valence shell.

Photoluminescence Properties of Cu+ Centers in MgS, CaS, SrS and BrS

The detailed emission and excitation spectra and the temperature dependence of the excitation efficiency are obtained for MgS:Cu+, CaS:Cu+, SrS:Cu+ and BaS:Cu+ at various temperatures between 16 and 293 K. In the excitation spectra of all the powder phosphors, two bands assigned to the intraionic transitions in the Cu+ ion are observed. The luminescence mechanism is explained by the isolated Cu+ ion model. The temperature dependence of the excitation efficiency suggests that the Cu+ ion in CaS, SrS and BaS occupies an off-center position of the sulfur octahedron.

Origin of the forbidden transitions in diluted magnetic semiconductors

Mechanisms for the intraionic optical transitions in Mn-based diluted magnetic semiconductors are analyzed on the basis of two possible models. A simple model for these transitions based on a proposal by Lacueva and Overhauser does not seem to be tenable. We conclude that the transition 6S → 4G observed in Cd 1− x Mn x Te and Zn 1− x Mn x Te is due to electric-dipole interactions made possible by the lack of inversion symmetry and the presence of the spin-orbit interaction.

Excitonic mechanism of luminescence excitation of rare-earths and transition metals in solids

We review here some new aspects of the spectroscopic properties of solids doped with transition metal (TM) and rare earth (RE) ions. The main emphasis is given to the evidence of binding of excitons by these ions, and to the impact of such “external excited states” on the efficiency of intra-ion transitions of REs and TMs. It is concluded that TM-, RE-bound excitons are a common feature in solids, and due to the impurity Auger processes play an important role in intra-ion excitation.

High pressure studies of optical properties and crystal lattice stabilit of ZnFeSe

Abstract The presence of iron ions in the ZnSe crystal lattice influences strongly the optical absorption properties of this semiconductor. We observed three different mechanisms of the absorption: the intra-ion transitions, photoionisation transition, and interband transition. The first two mechanisms originate from the presence of iron ions in the crystal. The pressure coefficients of intra-ion transitions were determined. The pressure red shift of ionisation spectrum was attributed to the transition of an electron from the valence band to the iron level. The influence of iron on the critical pressure for the phase transition from zincblende to rocksalt structure was also established.

Pressure dependence of the optical absorption edge of Cd1-xMnxSe.

The effect of pressure on the absorption edge of ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Se with different compositions has been measured. A pinninglike behavior has been observed for the mixed crystal with x=0.45, that is, the pressure coefficient decreases from about 6\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ eV/kbar at low pressures to almost zero at pressures Pg10 kbar. The pinning is attributed to the effect of the intraionic transitions of ${\mathrm{Mn}}^{2+}$. Furthermore, the energy of the absorption edge becomes independent of the polarization of incident light for the same sample at pressures at which the absorption edge is pinned, which confirms the above interpretation. The relation between phase-transition pressure and composition in ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Se is also presented.

Optical-absorption studies of wurtzite-phase Zn1-xMnxSe.

Optical-absorption results on single-crystal samples of ${\mathrm{Zn}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Se are presented. Dichroism associated with the fundamental edge is established for x\ensuremath{\ge}0.35, consistent with the onset of the wurtzite phase. Up to four absorption bands associated with ${\mathrm{Mn}}^{2+}$ intraion transitions are seen at x\ensuremath{\sim}0.50; the shifts of the three lowest transitions with x are analyzed with use of ligand-field theory applied to localized ${\mathrm{MnSe}}_{4}$ clusters. Consistent polarization in the Mn absorption spectrum occurs in the wurtzite region. Possible mechanisms leading to such polarizations are considered.

Pressure dependence of intra-ionic transitions of Mn2+ for the semimagnetic semiconductor Cd1-xMnxSe and Zn0.7Mn0.3Se under different temperatures

Using DAC high-pressure equipment, the optical absorption spectra of the ternary semimagnetic semiconductor alloy Zn0.7Mn0.3Se and Cd1-xMnxSe have been studied at room temperature, 77 K and under hydrostatic pressures of 0-45 kbar. Some absorption peaks are observed at the low-energy side of the absorption edge for Zn0.7Mn0.3Se and a pinning effect of the absorption edge is observed with increase of the pressure in Cd1-xMnxSe. The transition mechanism and the pressure coefficients are discussed in the light of crystal field theory and the pressure effect of their optical absorption edges is also discussed. The pressure dependences of the absorption edge for two polarisations of light with E//C and E perpendicular to C have been measured and discussed in connection with the transition mechanism.

Intraionic transition of d electrons for Mn 2+ ions in semimagnetic semiconductor Zn 0.7Mn 0.3Se under high pressure

The absorption spectra of ternary semimagnetic semiconductor alloy Zn 0.7Mn 0.3Se have been studied at 77K and under hydrostatic pressure in range of 0–45kbar by use of DAC high pressure equipment. Three absorption peaks associated with Mn 2+ are observed at low energy side of the absorption edge of Zn 0.7Mn 0.3Se and shift to lower energy with increasing pressure at the rates of −1.7, −1.5 and −2.7 × 10 −3eV/kbar, respectively. These peaks are attributed to the transitions of 6A 1→ 4T 2, 6A 1→ 4A 1+ 4E as well as 6A 1→ 4T 2(D), respectively, and their pressure behavior is discussed in the light of crystal field theory together with the pressure dependence of the absorption edge.

XANES and EXAFS studies on K-shell absorption in K 1−xNa xCl solid solutions

X-ray absorption measurements were made for Na K-edge on K 1−xNa xCl solid solutions at room and at low temperatures using synchrotron radiation. The prominent peak can be assigned as the exciton associated with intra-ionic transition of Na + ion. The small structure appearing in the edge is assigned as the exciton associated with the dipole-forbidden s-s transition. From the analysis of EXAFS spectra, it was concluded that the first shell distance around the sodium ion in the solid solution holds the value of the pure NaCl, and is insensitive to the concentration of NaCl in KCl.

Intra-manganese absorption and luminescence in Zn 1- xMn xSe semimagnetic semiconductor

Optical absorption and luminescence of Zn 1- x Mn x Se (0 < x < 0.53) is measured at T = 10, 77 and 300 K below fundamental absorption edge. Three absorption and one luminescence bands are observed and are attributed to the intra-ion transitions of Mn 2+ in 3 d 5 configuration. Crystal field parameter Dq and Racah parameters B and C are derived as well as stabilization energy.

Pulsed laser-induced photopotentials at the cobalt-photosensitized ZnO/electrolyte interface

The time-resolved photoelectrochemical behavior of Co 2+-photosensitized ZnO electrodes is investigated in the 10 −8−10 −2 s time domain using the pulsed laser-induced photopotential technique. The influence of various parameters, such as the excitation wavelength (365 or 640 nm), the open-circuit prepolarization potential, the presence of hydroquinone as a reducing agent in the electrolyte, as well as the electrode surface pretreatment is analysed qualitatively. Although the Co 2+:3 d 7 ions extend the ZnO photoresponse to the whole visible range when they occupy the tetrahedral position inside the lattice, they are shown to induce e −- h + recombinations which develop within multiple successive time domains and originate from either the surface or the depletion region of the electrode. The similar kinetic behavior of the ZnO:Co/electrolyte interface when excited in the UV (band-to-band transitions) or the visible (Co 2+:3 d 7 intra-ionic transitions) range, suggests that the photocarriers are always under control of the ZnO structure.

Excited state absorption of Ag --centres in RbBr

The induced absorption of Ag --centres in RbBr pumped by a strong excimer laser pulse is measured over a wide spectral range (250 to 950 nm) using a weak cw probe beam (Xe-lamp). A strong transient absorption around 510 nm is observed and is attributed to the intraionic transition from the relaxed excited 5 3P 1 state to upper S- or D-levels.

Potential material for electroluminescence devices in the visible region

High intensity photoluminescence response has been observed in the visible region (λ=600 nm) in a diluted magnetic semiconductor system Zn1−xMnxS (0.05≤x≤0.4) at 300 and 77 K for the first time. The temperature and concentration independent position of the observed peak can be attributed to the intraionic transition of Mn++. Considering the crystal field splitting parameter and Racah’s coefficient and using the diagram proposed by Y. Tanabe and S. Sugano [J. Phys. Soc. Jpn. 9, 753 (1954)], the luminescence transition responsible for the observed peak was found to be 4T1–6A1. On the basis of high luminescence response, Zn1−xMnxS could be a promising material for electroluminescence devices in the range where photopic response of the human eye is nearly maximum.

X-ray induced luminescence, photoluminescence and thermoluminescence of Bi4Ge3O12

X-ray induced luminescence, photoluminescence and thermoluminescence of nominally pure Bi4Ge3O12 crystals are studied within the 12K-295K temperature range. The broad emission band reported by other workers for radio- and photoluminescence is observed to present some structure. thermoluminescence spectra exhibit eight major glow peaks whose wavelength spectra present a structure similar to that of radio-and photoluminescence emissions. This structure is discussed in terms of Bi3+ intra-ionic transitions.

Identification of new absorption bands in Zn 1-xMn xTe

We report optical absorption measurements on Zn 1-xMn xTe at 300K, 77K, and LHe temperatures. In an x ∼ 0.6 sample, new absorption bands are found at 2.605 eV and 2.745 eV, together with two lower energy bands seen also in an x ∼ 0.1 sample. All bands are attributed to intra-ion transitions of Mn 2+ in the 3d 5 configuration.

Photoluminescence bands related to localized Mn2+ transitions in diluted magnetic semiconductors

Photoluminescence excitation measurements have been carried out on the diluted magnetic semiconductors Cd1−xMnxTe and Cd1−xMnxSe. The temperature dependence of the known 2.0 eV and 1.2 eV PL bands is discussed in terms of a configuration coordinate model involving Mn2+ intra-ion transitions. Two broad band emissions in Cd1−xMnxSe, at 2.13 eV and 1.35 eV, are reported which appear to be the analogies to the PL bands seen in Cd1−xMnxTe.

Surface photovoltage spectroscopy with cleaved GaAs (110) surfaces: Spectroscopy of Cr2+

Surface photovoltage spectra of clean (110) surfaces cleaved from n-type GaAs crystals doped with Te or Si exhibit two narrow peaks at 0.72 and 0.89 eV superimposed on a broad shoulder extending from h/ω≊0.7 eV to Eg. Both peaks are strongly increased by chemisorption of oxygen and by increasing the band bending. The peak at 0.89 eV is attributed to intra-ion 3d transitions of deep Cr2+ impurities, with the ground state 0.72 eV below the conduction band edge. The presence of chromium in the samples was proven by AES after anneals at 800 K, causing an enrichment of chromium near to the surface. The growth of the 0.89 eV peak proportional to the square of the surface potential is explained by an increase of the net escape probability from the excited state into the conduction band via tunneling.