Band In KBr Research Articles

Pressure dependence of spin-orbit effects in defect centers in ionic crystals

The absorption spectra of F center of CsBr have been measured at 1.5—80 K under pressures of 1 atm, 6 kbar and 11.4 kbar. Analysis of absorption line shapes has revealed that spin-orbit coupling increases with increasing pressure. Similar behavior of spin-orbit coupling under applied pressure has also been observed for the absorption bands in KBr:Tl+. These features are discussed comparing the results of pressure effects of the CsBr F band with those of the A, B, C absorption bands in KBr:Tl+ and KBr:In+. The pressure dependence of spin-orbit splitting for the CsBr F band has been estimated to be about 1.6 meV/kbar at 1.5 K.

Excitation spectra of activator luminescence—the observation of a new D absorption band in KBr:In crystals

Abstract We have investigated excitation spectra of the In+ ion luminescence directly excited by UV-light (6.1 to 6.4 eV) and creation spectra of the photostimulated luminescence, excited by F-band light after a preliminary monochromatic UV irradiation of KBr:In crystals with different In+ concentrations. Careful analysis of the excitation spectra allows us to detect a new D absorption band having a Gaussian shape with the following parameters: peak position at E0 = 6.375 eV and half-width ΔE = 0.14 eV, effective absorption cross-section at the band peak [sgrave]D, max = 6.9 10−16 cm2. The oscillator strength f = 0.12 of the D band and quantum yield η = 0.012 ± 0.001 of In+ luminescence excited in the D band are also determined.

Comparison between thermoluminescence and cathodoluminescence spectra of KBr and KCl.

The emission spectra of KBr and KCl were obtained in the temperature range 18--290 K during the thermoluminescence (TL) measurements and 40--300 K during the cathodoluminescence (CL) measurements. The 400--600 nm broad emission bands in KBr and KCl at low temperatures are resolved into at least two components: the self-trapped-exciton (STE) \ensuremath{\pi} emission and the \ensuremath{\alpha}-center emission by using different modulation frequencies in the CL work. This separation of component bands is supported by the TL measurements. The different temperature dependences of the STE emission in the CL and TL cases and the 50--90 K decay processes of the CL STE bands are discussed. The relation between the F-band self-absorption in KCl and the irradiation dose is also discussed.

Infrared spectrometric determination of nitrate, nitrite and ammonium ions by means of matrix isolation in pressed alkali metal halide pellets

A technique is proposed for the determination of ions by infrared spectrometry, based on ion exchange and matrix isolation in alkali metal halide pressed pellets. The sharpness of the vibrational bans of many of the matrix-isolated ions ensures high specificity, good quantification and low detection limits. The extent of applicability of this technique is surveyed and the experimental procedures that are required are presented. The application of the method to the determination of nanomole amounts of nitrate, nitrite and ammonium ions in water is described. Under suitably adjusted conditions, the incorporation of these ions in KBr and CsCl is complete and direct quantification is feasible. Quantification is also possible by the use of 15N-labeled internal standards. Nitrate and nitrite give much narrower bands in KBr than in CsCl whereas the opposite is true for ammonium ions. In general, optimum determinations may require different alkali metal halide matrices for different ions. The technique should be adaptable to the determination of many other polyatomic ions.

Lattice Relaxation of Self-Trapped Excitons in Binary Mixed Crystals of KCl and KBr

Change of emission bands in KCl 1- x Br x mixed crystals has been investigated at liquid helium temperature (LHeT) to make clear the nature of lattice relaxation of the self-trapped exciton (STE). When x <0.03, two emission bands appear at 3.60 eV and 4.88 eV. These emission bands have been confirmed to originate from a triplet state and a singlet state of localized excitons created at Br - dimer centers, respectively. With increase of x , the 4.88 eV band shifts gradually toward the low energy side to become finally the σ emission band in KBr ( x =1.0), but the 3.60 eV band diminishes on the way. Instead, a new emission band, which appears in the lower energy side, is connected to the π emission band in KBr. The discontinuity between the 3.60 eV band and the π band has been attributed to an additional lattice distortion characteristic to the initial state of the π emission. An off-center displacement of the Br 2 - core of the STE is suggested as a candidate for the type of the additional distortion.

Infrared spectrometric determination of nitrate, nitrite and ammonium ions by means of matrix isolation in pressed alkali metal halide pellets

A technique is proposed for the determination of ions by infrared spectrometry, based on ion exchange and matrix isolation in alkali metal halide pressed pellets. The sharpness of the vibrational bans of many of the matrix-isolated ions ensures high specificity, good quantification and low detection limits. The extent of applicability of this technique is surveyed and the experimental procedures that are required are presented. The application of the method to the determination of nanomole amounts of nitrate, nitrite and ammonium ions in water is described. Under suitably adjusted conditions, the incorporation of these ions in KBr and CsCl is complete and direct quantification is feasible. Quantification is also possible by the use of 15 N-labeled internal standards. Nitrate and nitrite give much narrower bands in KBr than in CsCl whereas the opposite is true for ammonium ions. In general, optimum determinations may require different alkali metal halide matrices for different ions. The technique should be adaptable to the determination of many other polyatomic ions.

Two types of lattice relaxation of self-trapped excitons in KClKBr mixed crystals3

Luminescent properties of excitons relaxed on Br − ions are studied in KCl crystal containing a small amount of bromine impurity (KCl:Br) and in KCl 1-xBr x mixed crystals. It is confirmed that both of 3.60 eV and 4.88 eV emission bands in KCl:Br originate from relaxed excitons localized at Br − ion pairs. No monomer band appears. Experimental results of KCl 1-xBr x mixed crystals suggest that the initial state of the π emission band in KBr should be accompanied with another type of lattice distortion in addition to the V K-type distortion. A candidate for this type of distortion will be off-center displacement of Br 2 − core of the self-trapped exciton.

Raman scattering induced by V centers and their aggregates in alkali halides

Abstract The Raman spectroscopy technique allows one to determine the nature of stable non-paramagnetic V-centers created in KI and KBr X-irradiated in the range 100–300 K. In the early stage of X-irradiation, trihalide ions X3- (X = I, Br) are created. They are characterized by the 111 cm−1 (KI) and the 175 cm−1 (KBr) stretching vibrational mode of the linear ion. The X3- ions are responsible for the V2 (about 350 nm) optical absorption band in KI and of the V4 (275 nm) band in KBr. By increasing the X-ray dose, polyhalide ions characterized by the I2 vibrational mode in In− (n = 5, …) ions are formed. In the case of KI, it is shown that the polyiodides are precursors of iodine aggregates which have the iodine crystal structure. Studies of KI (Ca2+) and KBr (Sr2+) near RT proves that the X3- ions are stabilized by the divalent cations.

Quadratic Jahn-Teller Effect in the Line Shapes of the A-Emission and A-Absorption Bands in KBr: Tl+-Type Phosphors

The adiabatic potential energy surfaces (APES's) of Tl + -type impurities in alkali halides, \(^{3}T_{1u}(\varGamma_{4}^{-})\) and \(^{3}A_{1u}(\varGamma_{1}^{-})\) have been calculated taking account of the spin-orbit interaction and both the linear and quadratic Jahn-Teller effect with the α 1 g and ε g vibrational modes. It has been found that the 3 T 1 u APES's have one kind of minima or the two kinds of minima, depending on whether we assume the linear or both the linear and quadratic Jahn-Teller interactions. A trap level 3 A 1 u lies just below both the minima. The line shapes of the A -emission and A -absorption bands in KBr: Tl + are calculated by using the Franck-Condon and Condon approximations. It has been found that the theoretical line shape of the A -emission band has the asymmetric doublet structure and reproduces the experimental emission bands A T and A X . This shows that the large energy differnce between the A X and A T bands is caused by the quadratic Jahn-Teller terms involving Q 1 (α 1 g ).

New metastable absorption bands in KBr

New metastable absorption bands, which appear as a broadening of the F and beta bands, have been observed in X-rayed KBr. They are very likely due to a perturbed F-centre or to a centre with an F-centre as a component.

Assignment of (Tl+)2 Absorption Bands in Alkali Halides by Magnetic Circular Dichroism Spectra

AbstractMagnetic circular dichroism spectra of absorption bands due to a Tl+ dimer center, i.e. (Tl+)2, in KI single crystals are investigated at temperatures from 25 to 300 K, which are compared with the spectra of (Tl+)2 bands in KBr and of (In+)2 bands in KCl. The absorption bands at 4.915 and 4.968 eV in KI:Tl+, which appear near the B‐band of Tl+ center, are attributed to the (Tl+)2 bands related to the B‐ and C‐bands, respectively.

High resolution spectroscopy of the A-band absorption structure

Experimental evidence on the triplet structure of the A absorption band in KBr: T1 is given. The results are obtained by means of the high resolution derivative technique that allowed us to reveal the true structure of the band without applying any external perturbation to further remove the degeneracy of electronic levels. A computer best fit was also used to obtain the parameters of the three subbands in the normal as well as in the derivative spectrum.

A‐luminescence of alkali halides activated by monovalent mercury‐like ions

AbstractPolarization is found of the long‐wave A‐luminescence bands in KI:Tl, KI:In, KBr:In crystals at 7 K. It is established that the dependence of the polarization degree on azimuth corresponds to oscillator emission along the crystal axis [111]. These bands are assumed to be due to “trigonal” Jahn‐Teller minima of the activator 3T1u excited states. It is established that the 400 nm band in KBr:T1 crystal represents emission from the trigonal minimum of the metastable 3A1u‐state of the activator. A doublet structure of the short‐wave A‐luminescence bands is found and investigated. The hypothesis is made that the structure is connected with the presence of two types of tetragonal Jahn‐Teller minima of the activator 3T1u excited states.

Thermomodulated A-band absorption of KBr: Tl

A marked oscillator-strength decrease of the A band in KBr: Tl has been pointed out by means of thermally-modulated optical measurements throughout the temperature range 88–380°K. The experimental results suggest the existence of a clear correlation between the states responsible of the absorption bands and are discussed in order to clarify the role of the thermal perturbation upon Tl + energy levels.

Optical absorption of s2configuration ions in alkali halide crystals: I. Lineshape of the A band in In+-doped crystals

The lineshape of the A band in KBr:In+ and KCl:In+ has been measured as a function of temperature from about 16K to room temperature. The shape of the A band is well accounted for at low temperatures by a model that allows for spin-orbit coupling, vibrational coupling of the mod A), mod B) and mod C) states, and the dynamical Jahn-Teller effect in the perturbed mod A) state. The principal factor governing the lineshape is the coupling with modes of T2g symmetry but agreement with the experimental results is much improved by a convolution of this calculated lineshape with a Gaussian function which represents the interaction with modes of A1g symmetry. The model fails, however, to account satisfactorily for the relative peak heights of the two components of the A band at high temperatures.

Optical absorption of s2configuration ions in alkali halide crystals: II. Lineshape of the C band in KBr:In+

For pt.I see ibid., vol.8, p.851 (1975). The lineshape of the C band in KBr:In+ has been measured as a function of temperature from 21K to room temperature. The band does not display obvious fine structure at any temperature but the appearance at the higher temperatures of two shoulders in addition to the main peak indicates a triplet structure. The lineshape of the C band is accounted for quantitatively in terms of a model that includes spin-orbit coupling, vibrational coupling to the mod A) and mod B) 11 0BC 2K state. The asymmetry of the C band is due to the states, the dynamical Jahn-Teller effect due to the trigonal T2 gamma modes and coupling to modes of A1g symmetry, in the perturbed mod C) state. The asymmetry of the C band is due to the quadratic terms in the Hamiltonian and although such terms would also arise from a difference in force constants in the ground and excited states, it is not necessary to introduce this effect to account for the lineshape in KBr:In+.

A high pressure search for K′‐bands in KBr and KI

AbstractThe optical F‐band in KBr has been studied at pressures up to 11 kbar and in KI up to 9 kbar. No new absorption bands were found to appear nor was any other anomalous behavior observed. It is thus shown that so‐called K′‐bands observed by previous investigators and the K′‐center to which they were attributed do not in fact exist in crystals subjected to hydrostatic pressure.

Optical Absorption Spectra of the A Band in KBr:Pb2+ Crystals

The shape of the A band in KBr:Pb2+ has been studied at various temperatures between 13 and 296 K. The band is almost symmetric at low temperatures but slightly asymmetric at high temperatures. The observed line shape of the A band in KBr:Pb2+ is discussed in terms of the Jahn–Teller effect and is compared with that of the A band in In+ and Tl+ doped alkali halides.

The enhancement of the F center production and the composite structure of the V 1 band in Kbr;Na crystals

The H center interaction with Na + impurity ions in KBr results in the subtle enhancement of the F center production at LNT. This was attributed to the formation of different two types of HNa + complex centers.

Thermo-chemical reactions of freed halogen interstitials in KBr;Na

The thermal annealing of the V 1 band in KBr;Na is studied. It was found that this band is made up of three different centres having trap depths of 0.23, 0.27 and 0.30 ± 0.03 eV, respectively. Thermal decay of these centres, accompanied with TL emission, obeys first order kinetics and results in the conversion into V 4 or V(306) centres as well as in the recombination with F centres. The ratio between conversions and recombinations was obtained for these centres.