F. Lanzl

A trigonal color center in NaF

Uniaxial stress splitting experiments suggest the 5456 Å zero-phonon line in NaF to be due to a transition of the F3+ center. The line and a number of phonon-assisted peaks are observed in absorption and emission.

Linear Stark effect of the F3+ center in LiF and NaF

Abstract A linear Stark effect is observed with the ionized R center in λ-irradiated alkali halides by studying the zero-phonon absorption lines 4874 A in LiF and 5456 A in NaF in high electric fields.

Momentenanalyse der R 2 -Nullphononen-Linie in NaF unter einaxialem Druck

The R2 zero-phonon absorption line 4480 Å in NaF at 4.2 °K and 23 °K is studied under uniaxial stress along 〈100〉 and 〈100〉. According to the F3 model of theR center the R2 line is found to be due to a transition between a degenerate ground state (2E) and a nondegenerate excited state (2A) of this center. Instead of a splitting into single components under stress, changes in line shape are observed which are analyzed by means of the method of moments. The zeroth and first moment of the line are calculated as functions of the magnitude of stress and temperature. The theoretical moments are found to be in good agreement with those determined from the experimental data. From a comparison of the measured moments with the theoretical expressions the stress splitting parameters are obtained which describe the removal of both the orientational and the orbital degeneracy of theR center under uniaxial stress. The corresponding strain parameters of the R2 line in NaF are compared with those in other alkali halides.

Pseudo Stark and uniaxial stress splitting of the 6955 Å zero-phonon line in LiF

Pseudo Stark and uniaxial stress splitting is observed with the zero-phonon line 6955 Å in LiF at 4.2 °K. From the combination of the results obtained by means of both methods it is concluded that the corresponding color center hasC2v point symmetry. The twofold rotation axis of the center and the transition dipole moment are oriented along 〈110〉 perpendicular to each other. On the basis of the results a few models of aggregate color centers are discussed. The theory necessary for the interpretation of the electric and uniaxial stress spectra of lines associated with rhombic 〈110〉 centers is presented including the numbers, intensities and energy shifts of the splitting components.

Moment analysis of the Stark effect of the R2 zero-phonon line in LiF at 4.2°K

Abstract By studying the R 2 zero-phonon absorption line in X-irradiated LiF in high electric fields a linear Stark effect of the R center is observed at 4.2°K. The analysis of the experimental results is performed using the method of moments. The results are in good accordance with the theory for E → A transitions of a C 3v center. By cooling the crystals from 4.2°K to 1.7°K the zero-field splitting of the R center ground state is found to be -1 .

A holographic information decoding method

Abstract The compensation of an extended source hologram is achieved by a second hologram negative.

Analysis of R and N1 Center Absorption Structures in NaF

The shape of the optical absorption structure caused by an electronic transition of a color center depends on the strength of the electron-phonon coupling parameter S. S can be interpreted as the most probable number of phonons involved in the transition. In the case of weak coupling (S « 1) only a sharp zero-phonon line occurs, whereas for strong coupling (S > 8) only a broad and smooth multiphonon band is observed. Intermediate coupling gives rise to both a zero-phonon line and a detailed multiphonon structure [l] as it can be seen in figure 2.

Farbzentren rhombischer und monokliner Symmetrien in NaF

A number of zero-phonon absorption lines ofF aggregate color centers is studied inx-irradiated NaF crystals under uniaxial stress. The color centers associated with the lines are found to exhibit rhombic (D2h, D2, C2v; rotation axes along 〈110〉 and 〈100〉) and monoclinic (C2h, C2, Cs; rotation axis along 〈110〉) symmetries. The transitions of the rhombic color centers correspond to 〈100〉 and 〈110〉 dipoles, those of the monoclinic centers to 〈112〉 and 〈110〉 dipoles. The most prominent line at 5803 Å is due to a 〈112〉 dipole transition within a monoclinic color center. Several models of centers are discussed.