Centers In KCl Research Articles

On the growth of Z1centres in microcrystalline powders of γ-irradiated KCl:Ca: the effect of particle size

The effect of particle size on the growth of Z1 centres in KCl:Ca is studied with the help of thermoluminescence measurements. The Z1 centres are more easily formed than F centres at higher concentration; this formation is achieved by reducing the particle size. It is argued that the dislocation densities and mobilities are the primary factors governing the growth of Z1 centres.

Efficient CW color center laser operation in the 1.7 to 2.2 μm range based on F +2 -like centers in KCl:Na +:O −2 crystals

A new color center laser is described which is based on F + 2 -like centers in additively colored KCl:Na +:O - 2 crystals. Pumped by the 1.32/1.34 μm lines of a Nd 3+:YAG laser, cw laser operation has been obtained with a wide tuning range from ≈ 1.71 to 2.15 μm. At 3W pump power the laser output power is ≈270 mW at 1.9 μm in the peak of the tuning curve. In order to maintain nonfading laser operation at 77 K the crystal has to be irradiated with auxilliary F band light.

An Impurity Center in KCl and NaCl Crystals Grown in Nitrogen Gas

An Impurity Center in KCl and NaCl Crystals Grown in Nitrogen Gas

Application of lasers withFA(II) color centers in KCl:Li crystals in intracavity laser spectroscopy

It was found that lasers utilizing color centers in KCl:Li can be employed in intracavity laser spectroscopy. The intracavity absorption spectrum of the atmosphere was recorded in the 3788–3793 cm−1 range.

Dislocation motion in photomechanical effects and the lifetime of photochemical products of the F-center in alkali halides

A simple theory describing photomechanical effects in colored alkali halides was proposed based on statistical dislocation dynamics. From the present theory together with empirical data on photomechanical measurements, the lifetime of the F --center in KCl is found to be about 2 s at around RT and the relevant activation energy is 0.29 eV.

Effects of the off-center position of the Li+ ion on the optical properties of the FA center in KCl.

The off-axis symmetry of the ${F}_{A}$ center in KCl:${\mathrm{Li}}^{+}$ has been investigated by optical experiments. We have studied static and dynamic reorientational properties of the ${F}_{A}$ center by measurements of absorption and emission. The off-axis model of the center has been confirmed. A theoretical treatment, which takes into account the small deviation of the center with respect to the crystal axes, is in good agreement with the experimental results. Best fittings of the theory to the experimental data yield a value of the off-axis angle theta=8\ifmmode^\circ\else\textdegree\fi{}.

Effects of pressure on the VK center in KCl.

The effects of isotropic pressure on the relaxation and optical-absorption spectra of ${\mathrm{Cl}}_{2}$${\mathrm{}}^{\mathrm{\ensuremath{-}}}$ in KCl are presented. This study is based on an extended Mott-Littleton relaxation calculation for KCl:${\mathrm{Cl}}_{2}$${\mathrm{}}^{\mathrm{\ensuremath{-}}}$ as a function of lattice constant using the hades program. The calculations show relatively little effect of pressure on the properties of the ${V}_{K}$ center (${\mathrm{Cl}}_{2}$${\mathrm{}}^{\mathrm{\ensuremath{-}}}$) until the lattice constant drops below \ensuremath{\sim}3.0 A\r{}. Below this value of the lattice constant, there are substantial changes in the relaxation effects and optical spectrum predicted. Comparisons with normal MCl:${\mathrm{Cl}}_{2}$${\mathrm{}}^{\mathrm{\ensuremath{-}}}$ ${V}_{K}$ centers and hybrid KX:${\mathrm{Cl}}_{2}$${\mathrm{}}^{\mathrm{\ensuremath{-}}}$ ${V}_{2}$ centers are also presented. We conclude that in KCl, the optical and spin-resonance spectra should show a clear change in their pressure dependence beyond a threshold. This threshold is not related to the phase transition in crystal structure.

On the deformation effect on Z1 centres in KCl:Sr

On the deformation effect on Z₁ centres in KCl:Sr

Formation of charged N1 centers in KCl and KBr

This paper reports the results of studies on charged N1 centers, produced using a technique in which additively colored KCl and KBr crystals are exposed to near ultraviolet excitation at low temperatures. In undoped crystals, absorption and emission data are presented showing several new charged N1 transitions along with information relating to the nature of the defects. In addition, this work demonstrates that in sodium-doped crystals, N1 centers can be ionized through electron transfer to FA centers. This technique has already been used in stabilizing (F+2)A centers in laser-active crystals and may have future application for lasing ionized N1 centers.

Site-switched Tl0 atoms in Tl+-doped NaCl and KCl.

The properties of two new ${\mathrm{Tl}}^{0}$-atom defects with orthorhombic symmetry ([11\ifmmode\bar\else\textasciimacron\fi{}0], [001], [110]) and which occur together with the well-known ${\mathrm{Tl}}^{0}$(1) center are studied in KCl:TlCl and NaCl:TlCl using electron-spin-resonance and optical-absorption techniques. On the basis of their production and their thermal and optical properties and taking into account the results of the hyperfine-interaction analysis it is concluded that these centers consist essentially of a ${\mathrm{Tl}}^{0}$ atom on an anion site (possibly perturbed by one or more cation vacancies), and that their production involves a site switching of the ${\mathrm{Tl}}^{0}$ atom in the ${\mathrm{Tl}}^{0}$(1) center. A Jahn-Teller distortion determines the symmetry of these defects and yields a ground-state p orbital oriented along a 〈110〉 direction. Similar site-switched models were proposed earlier for orthorhombic ${\mathrm{In}}^{0}$ and axial ${\mathrm{Ga}}^{0}$ centers in KCl, and it is shown that these centers possess many features in common with the orthorhombic ${\mathrm{Tl}}^{0}$ centers. One of the latter centers is optically very stable and forms the dominant defect in NaCl:TlCl while it is not produced in KCl. Optical-absorption bands at 430 and 560 nm are attributed to this center.

Optimization of FA(II) and FB(II) color-center lasers

We have studied the performance of color-center lasers based on FA(II) and FB(II) centers in KCl and RbCl with the intent of simultaneously maximizing their output power and tuning range. We have achieved a combined tuning range of 2.22–3.64 μm and slope efficiencies as high as 10%. We also find these centers to be totally free of photodegradation effects during laser operation and to be storable without deterioration at temperatures below 0°C.

Formation of the Tl°(1) Center in KCl

Analyse des spectres d'absorption visible et IR de KCl:Tl, a la temperature de l'azote liquide apres irradiation gamma et irradiation a 460 nm. Mise en evidence du role des centres Tl 2 + dans la formation des centres Tl 0 (1)

TRAJECTORY TREATMENT OF THE FA (II) -CENTER IN KCl : Li DECAY TIME IN THE EXCITED STATE

We simulate the temperature dependence of the decay time of an impurity in its exicetd state by obtaining the classical trajectories of the ions in the crystal. The FA (II) -center in KCl : Li is treated.

The role of state of dispersion of impurity on Z1 centres in KCl:Ba2+ crystals

The role of state of dispersion of impurity on Z1 centres in KCl:Ba2+ crystals

Treatment of the relaxed F center in KCl with the recursion method.

Ham's vibronic model for the relaxed excited state of the F center in KCl is investigated with a new approach based on the recursion method. We have calculated the energy and the wave function of the ground vibronic state and the lowest excited state, the dichroism in light emission in the presence of external fields (magnetic field, electric field, uniaxial stress), and the temperature dependence of the polarization induced by the electric field and by the uniaxial stress. Ham's vibronic model is found to account satisfactorily for the above properties. The perspectives of the recursion procedure for studying coupled electron-phonon systems are discussed.

Hyperfine behavior of the laser-active Tl 0(1) center in alkali-halides

The hyperfine parameters, obtained from an electron-spin-resonance study, of the laser-active Tl 0(1) center in four alkali-halides have been analysed and compared to the Tl 0(2) center results. It is shown that the anisotropic contribution to the hyperfine components is virtually the same for all the Tl 0 centers but that the isotropic contribution varies widely in size and sign. This is attributed to the varying amount of s-mixing caused by the varying odd crystal-field component throughout the alkali-halides for the Tl 0(1) center. For Tl 0(2) such s-mixing does not occur because this center possesses inversion symmetry. The results obtained show that an analysis of the hyperfine components provides a powerful tool to determine whether or not a given np 1 atom or ion center is positioned in a crystal field possessing inversion symmetry. As an illustration the hyperfine parameters of some Pb +(6 p 1) centers in KCl and RbCl are analyzed.

Emission spectra and decay kinetics of the A-band emission from Pb2+centres in KCl and KI single crystals

The emission spectra of KCl:Pb2+ and KI:Pb2+ excited in the A-absorption band at various temperatures are reported. The temperature dependence of the decay time of the A-band emission from KCl:Pb2+ and KI:Pb2+ is also investigated. The results are interpreted in terms of a model that includes the Jahn-Teller effect, the spin-orbit interaction, and an additional perturbation caused by either a next-nearest neighbour or a nearest neighbour cation vacancy; the spin-orbit interaction is assumed to be stronger than the Jahn-Teller effect. The temperature dependence of the decay kinetics of both KCl:Pb2+ are well described by this model.

Depolarisation dynamics of hot luminescence in F centres

A theory for the depolarisation dynamics of hot luminescence in the F centre in KCl is worked out on the basis of a vibronic model. The hot luminescence spectrum is calculated by using eigenvalues and eigenstates of a pseudo-Jahn-Teller system composed of 2p and 2s states coupled to a1g and t1u phonon modes, within the Markov approximation for the vibronic relaxation. Because of the pseudodegeneracy, the 2p to or from 2s nonradiative transition occurs at every step of the relaxation, resulting in the depolarisation of the hot luminescence in agreement with the observed spectrum obtained by a recent experiment.

Optical detection of the magnetic resonance of color centers

Optical detection of magnetic resonance applied to the F center in KCl is presented. The advantages and the theoretical basis of the technique of optical detection of magnetic resonance are discussed, and a description of the details of the actual spectrometer designed for the study of color centers is given. The successful observation of the optical detection of the resonance of the KCl F center is reported.

Relaxation along a single pathway in a quasicontinuum of modes: A trajectory treatment of the FA(II) center in KCl:Li.

The excited-state configuration of ${F}_{A}$(II) has been modeled by a potential that is stable (harmonic) for all displacements except one (${Q}_{\mathrm{vac}}$) in which neighbor-correlated passage of the vacancy occurs between equivalent 100-type positions. Solving classical equations of motion for atomic displacements we derive the time of residence in the initially excited-state configuration, as well as decay and correlation times for the dephasing of ${Q}_{\mathrm{vac}}$. The times range between a few and some ten Debye periods and decrease with increasing temperature. Results are comparable with relaxation times measured by Wiesenfeld, Mollenauer, and Ippen in KCl:Li. Their quantum-mechanical calculations are justified in terms of our model.