Band In KCl Research Articles

Effect of Impurities on the F Band in KCl

First Page

A, B and C Bands in KCl : In and KCl : Sn

Absorption spectra of KCl:In and KCl:Sn are studied at various temperatures, and all the A, B, C and D bands corresponding to those well known in KCl:Tl are found. In KCl:In, the intensities of the A, B and C bands are proved to be proportional to the concentration of In + ions. The ratio of the dipole strength of the C band to that of the A band is found 54 in KCl:In and 18 in KCl:Sn. The position of the B band is 267 mµ (4.64 eV) in KCl:In and 251 mµ (4.9 eV) in KCl:Sn. The relation between the dipole strength and the position of the B band seems to support the theory given by Sugano. Further, it is found that both the A and D bands have a multiplet structure, the A band a doublet and the C band a triplet, both in KCl:In and KCl:Sn. Their origin is discussed.

Electron Spin Resonance of theZ1Band in KCl with SrCl2

The electron spin resonance (ESR) associated with the ${Z}_{1}$ optical absorption in KCl: Sr has been observed in association with the $F$-center ESR. By an extrapolation procedure, it is found that the ${Z}_{1}$ ESR is characterized by a $g$ value of 1.9952\ifmmode\pm\else\textpm\fi{}0.0005 and a derivative peak-to-peak width of 63\ifmmode\pm\else\textpm\fi{}1 Oe. A Gaussian shape for the ${Z}_{1}$ ESR is strongly inferred. Preliminary results obtained with $F$ and ${Z}_{2}$ centers present indicate that the ${Z}_{2}$ ESR has a slightly larger $g$ value and a somewhat greater width than the ${Z}_{1}$ ESR. Optical absorption parameters of $h{\ensuremath{\nu}}_{max}=2.068\ifmmode\pm\else\textpm\fi{}0.005$ eV (599 m\ensuremath{\mu}) and $W=0.290\ifmmode\pm\else\textpm\fi{}0.005$ eV are found for the ${Z}_{1}$ band at liquid nitrogen temperature.The ESR results are compared to earlier measurements by Kawamura and Ishiwatari. An attempt is made to interpret the results by comparing Seitz's model of the ${Z}_{1}$ center to the $F$ center. There are tentative indications that Seitz's model may be appropriate, but the calculations are not yet sufficiently refined to establish the model with any degree of certainty. An estimate is made of the rather large hyperfine interaction to be expected for ${Z}_{1}$ centers containing ${\mathrm{Sr}}^{87}$ nuclei.

Z bands in KCl

Z bands in KCl

Growth and Bleaching of the Z1 Band in KCl Doped with Divalent Impurities

AbstractThe rate of F and Z1 center formation by X‐irradiation is studied at different temperatures in doped KCl crystals; at 0°C and at room temperature the slow but fully reproducible, growth of a Z1 band is found, but this attains only a low saturation value. The results can be interpreted by assuming that the X‐rays have an additional bleaching effect which is stronger for the Z1 than the F centers. The effects of free holes in the valence band (obtained by optical stimulation of V centres) on these centers is also studied at different temperatures, and the ratio of the capture cross sections for holes, σ/σ is determined, the values ranging from 2.1 (at liquid nitrogen temperature) to 1.5 (at room temperature).

Reactions among Point Defects in Alkali Halides

Existing knowledge of point defects and their interactions in uncolored alkali halide crystals is briefly reviewed. Attention is drawn to recent experimental and theoretical work which indicates that vacancy pairs are not highly mobile defects. This has important implications for some hypotheses on the kinetics of color center reactions at low temperatures. This knowledge of defects in uncolored crystals is then applied to a discussion of the reactions which may take place between F centers and impurity ions in additively-colored doped crystals and the theoretical possibilities are compared with experimental information on Z centers. Consideration of the thermodynamic equilibria in these reactions seems to eliminate the Z1 and Z2 centers of Pick as possible causes of either of the Z1 and Z2 absorption bands in KCl. (The Z2 model of Pick is identical with the Z1 model of Seitz and is a divalent impurity cation which has trapped an electron.) Two possible centers for the Z2 band presen tthemselves; (a) an associate of an F center with a divalent cation and (b) an associate of an F center with an impurity-vacancy pair (the Z2 model of Seitz). The structure of the Z1 center is not resolved by these considerations. Attention is drawn to some paradoxical experimental results on Z1 and Z2 centers and further experiments to resolve outstanding questions are suggested.

�ber die optische Absorption von Schichten aus PbCl2 und des Systems TlCl-KCl

In the first part of this paper the optical absorption of amorphous films of PbCl2, formed by quenching condensation, is shown and compared to the spectrum of PbCl2 in its normal state. The sharp exciton band of crystalline PbCl2 in the long wavelength region is considerably broadened in the spectrum of amorphous films. The transition from the amorphous state to the normal crystalline state is indicated by an abrupt, irreversible change in the absorption curve at 260‡ K. This comparatively high temperature of crystallisation seems to be due to the complicated structure of PbCl2. In the second part of this paper the optical absorption curves of evaporated films of the system TlCl-KCl are measured. A shift of the absorption bands as a function of the composition is found. The 3,46-eV-maximum of pure TlCl is coordinated to the A-band of the KCl∶Tl-phosphor. On the other hand there is no connection between the 5,82-eV-maximum of TlCl and the known bands of KCl∶Tl.

Alpha and beta bands in KCl and NaCl

Alpha and beta bands in KCl and NaCl

Effect of Pressure on the M Center in Alkali Halide Crystals

The effect of pressure to 52 800 atm has been measured on the M band in NaCl, KCl, KBr, and KI, and on the R2 and N bands in KCl. In general, the band peak shifts to higher frequency with increasing pressure for all bands. At the phase transition from fcc to sc there is a blue shift in KCl, but a red shift in KBr and KI. It is suggested that the shift corresponds to a balance between contraction and polarizability effects. From an Ivey-type relation, it would seem that the M center is somewhat less compressible than the F center. There is a marked increase in intensity of the M center in the potassium halides in going through the phase transition from the fcc to the sc lattice.

Absorption and Excitation Bands of KCl–Tl in the Extreme Ultraviolet Region

Absorption and Excitation Bands of KCl–Tl in the Extreme Ultraviolet Region

Symmetry Properties of theV1Center

The symmetry of the ${V}_{1}$ center was studied using a technique of bleaching with polarized light. The ${V}_{1}$ band in KCl and KBr produced by x-rays and 2-Mev electron bombardment was examined. In addition, the effect of bleaching with polarized light on the phosphorescent emission of KCl was observed. It is concluded that the center responsible for the ${V}_{1}$ absorption band in KCl and KBr has cubic symmetry insofar as its optical absorption is concerned. The phosphorescent emission of KCl became anisotropic under polarized bleaching light, indicating the presence of a center of noncubic symmetry. This second center has a [011] axis of symmetry.

Configuration Coordinate Curves forF-Centers in Alkali Halide Crystals

Measurements have been made of the $F$-center absorption band in KCl, KBr, KI, NaCl, and LiF in the range from 4\ifmmode^\circ\else\textdegree\fi{}K to 300\ifmmode^\circ\else\textdegree\fi{}K. Analysis of these data shows that the important ionic vibrational frequency influencing the $F$-center is considerably lower than that of the lattice, indicating that a configuration coordinate curve model may be the appropriate one to use, rather than the continuous dielectric model. Using the peak of the $F$-center emission bands as determined by Botden, van Doorn, and Haven, and the present absorption data, configuration coordinate curves are computed for the ground and excited state curves of $F$-centers in KCl, KBr, KI, and NaCl. Using these curves, predictions of the emission band-widths are found to be in agreement with experiment except for the case of KCl. The low efficiency of $F$-center luminescence may be understood by applying the criterion for luminescence proposed by Dexter, Klick, and Russell to these configuration coordinate curves.