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Inhomogeneous broadening of the optical spectra of Yb3+ in phosphate glass
Vol. 8, No. 9
f~,.+ 2f~+
ABSTRACTS OF PAPERS TO APPEAR IN
10.0 ±5%; YFeO3, fe,. + 2f~+ = 11.0 ±1.0%; LaCrO3, f~ = 1.63 ± ions 0.6%; disCaMnO3, f~ = 3.3 ± 0.8%. For thebyd neutron and crepancies between f~ determined resonance methods are explained in terms of spin polarisation effects and revised estimates of f~= 2.7 ±0.6% (LaCrO 3) and ~ = 5.3 ±0.8% (CaMnO3) are presented. Consideration of charge transfer suggests f~+ f~is about 3.0% in LaCrO3. =
Received 3 Febraary 1970 8.
IMPROVED DEBYE—WALLER FACTORS FOR SOME ALKALI HALIDES John S. Reid and T. Smith, Department of Natural Philosophy, The University, Aberdeen, AB9 2UE, Scotland.
Calculated Debye—Waller Bk factors are tabulated for the alkali halides NaF, NaC1, NaBr, Na!, KC1, KBr in the temperature range 5°K—295°K.The calculations were made by sampling eigendata given by fitted shell models at 64 000 points in the Brillouin zone. Errors introduced by this sampling are shown, and the effect of the quasiharmonic frequency changes and the zerophonon terms is discussed in detail. The high and low temperature limits of the Debye Temperature HU and several associated thermodynamic quantities for the sodium halides are also given. A comparison with experimental values indicates that there is not yet an entirely satisfactory agreement with the calculations. Received 15 January 1970
Revised 9 Marc/i 1970 9.
HOT EXCITONS AND EXCITON EXCITATION SPECTRA E. Gross, S. Permogorov, V. Travnikov and A. Selkin, Institute of Semiconductors, Academy of Sciences of the USSR, Leningrad. Excitation Spectra (E.S.) of free exciton emission in CdS crystals are measured at 4.2 and 77°Kboth for zero-phonon emission lines (n=IA, n=IB and n=2A) and for line of exciton annihil-
J.
PHYS. CHEM. SOLIDS
iii
ation with simultaneous creation of LO phonon (A1—LO). structure with Distinctly energypronounced period of LO oscillating phonon can be observed in the E.S. of all exciton emission lines. This structure arises due to kinetic energy relaxation proccesses in exciton bands, the appearance of oscilations is conditioned by incomplete thermalization of ecitons during exciton life-time. Observation of discrete structure in the E.S. permits one to draw some conclusions concerning the mechanism of exciton formation under optical excitation. Creation of excitons with kinetic energies up to 0.2 eV, considerably exceeding the binding energy 0.03 eV, was observed. Non-equilibrium character of zero-phonon free exciton emission is briefly discussed. iS’~ceived7 November 1969 Revised 9 A/arch 1970 10.
ORBACH TYPE REORIENTATION PROCESSES IN THE PARAELASTIC RELAXATION OF 0 IN KC1 C. Pfister and M. BOsch, Laboratory of Solid State Physics, Swiss Federal Institute of Technology, Zurich.
In the reorientation of o molecule ions in KC1 under uriiaxial stress a process occurs which can be regarded as an Orbach type process. A detailed experimental study of this process has been performed. The results are discussed in terms of rate equations and of the one photon transition probability derived by Gosar and Pirc. The theoretical predictions are in excellent agreement with the experimental results. From the analysis the effective tunneling matrix elements, the effective moments of inertia and the potential barrier for the rotation by 900 are obtained. Received 10 February 1970
11.
INHOMOGENEOUS BROADENING 3~ OFIN THE OPTICAL SPECTRA OF Yb PHOSPHATE GLASS J T. Fournier, Central Research Laboratory, American Optical Corporation, Southbridge, Massachusetts 01550 and R.H. Bartram, Physics Department
iv
ABSTRACTS OF PAPERS TO APPEAR IN and Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06268
The observed widths and asymmetries of the spectral lines of Yb3~in phosphate glass are attributed to systematic site-to-site variations in the crystal field at the rare earth. A model rare earth site consisting of a Yb3~ion coordinated by three P0 4 tetrahedra is considered. A cornpliant mo~ieof distortion of the complex is identified, and it is shown that a distribution of distorted sites can lead to lineshapes which reproduce many of the features of the observed spectra. Using a point-ion model, the crystal field at the rare earth site is calculated as a
J.
PHYS. CHEM. SOLIDS
Vol. 8, No. 9
function of a single configuration co-ordinate which describes the distortion. The electrostatic energy of the complex is also determined as a function of the configuration coordinate, and the lineshapes are computed from the crystal—field levels assuming a Boltzmann distribution. Because of uncertainty in the structural parameters of the glass, the effect on the lineshapes of vanations in the dimension of the complex and in the charge states of the ligands is considered. The crystal—field parameters are scaled to compensate deficiencies in the point-ion approximation, and the effect on the lineshapes of changes in the scale factors is discussed. Received 9 February 1970
f~,.+ 2f~+
ABSTRACTS OF PAPERS TO APPEAR IN
10.0 ±5%; YFeO3, fe,. + 2f~+ = 11.0 ±1.0%; LaCrO3, f~ = 1.63 ± ions 0.6%; disCaMnO3, f~ = 3.3 ± 0.8%. For thebyd neutron and crepancies between f~ determined resonance methods are explained in terms of spin polarisation effects and revised estimates of f~= 2.7 ±0.6% (LaCrO 3) and ~ = 5.3 ±0.8% (CaMnO3) are presented. Consideration of charge transfer suggests f~+ f~is about 3.0% in LaCrO3. =
Received 3 Febraary 1970 8.
IMPROVED DEBYE—WALLER FACTORS FOR SOME ALKALI HALIDES John S. Reid and T. Smith, Department of Natural Philosophy, The University, Aberdeen, AB9 2UE, Scotland.
Calculated Debye—Waller Bk factors are tabulated for the alkali halides NaF, NaC1, NaBr, Na!, KC1, KBr in the temperature range 5°K—295°K.The calculations were made by sampling eigendata given by fitted shell models at 64 000 points in the Brillouin zone. Errors introduced by this sampling are shown, and the effect of the quasiharmonic frequency changes and the zerophonon terms is discussed in detail. The high and low temperature limits of the Debye Temperature HU and several associated thermodynamic quantities for the sodium halides are also given. A comparison with experimental values indicates that there is not yet an entirely satisfactory agreement with the calculations. Received 15 January 1970
Revised 9 Marc/i 1970 9.
HOT EXCITONS AND EXCITON EXCITATION SPECTRA E. Gross, S. Permogorov, V. Travnikov and A. Selkin, Institute of Semiconductors, Academy of Sciences of the USSR, Leningrad. Excitation Spectra (E.S.) of free exciton emission in CdS crystals are measured at 4.2 and 77°Kboth for zero-phonon emission lines (n=IA, n=IB and n=2A) and for line of exciton annihil-
J.
PHYS. CHEM. SOLIDS
iii
ation with simultaneous creation of LO phonon (A1—LO). structure with Distinctly energypronounced period of LO oscillating phonon can be observed in the E.S. of all exciton emission lines. This structure arises due to kinetic energy relaxation proccesses in exciton bands, the appearance of oscilations is conditioned by incomplete thermalization of ecitons during exciton life-time. Observation of discrete structure in the E.S. permits one to draw some conclusions concerning the mechanism of exciton formation under optical excitation. Creation of excitons with kinetic energies up to 0.2 eV, considerably exceeding the binding energy 0.03 eV, was observed. Non-equilibrium character of zero-phonon free exciton emission is briefly discussed. iS’~ceived7 November 1969 Revised 9 A/arch 1970 10.
ORBACH TYPE REORIENTATION PROCESSES IN THE PARAELASTIC RELAXATION OF 0 IN KC1 C. Pfister and M. BOsch, Laboratory of Solid State Physics, Swiss Federal Institute of Technology, Zurich.
In the reorientation of o molecule ions in KC1 under uriiaxial stress a process occurs which can be regarded as an Orbach type process. A detailed experimental study of this process has been performed. The results are discussed in terms of rate equations and of the one photon transition probability derived by Gosar and Pirc. The theoretical predictions are in excellent agreement with the experimental results. From the analysis the effective tunneling matrix elements, the effective moments of inertia and the potential barrier for the rotation by 900 are obtained. Received 10 February 1970
11.
INHOMOGENEOUS BROADENING 3~ OFIN THE OPTICAL SPECTRA OF Yb PHOSPHATE GLASS J T. Fournier, Central Research Laboratory, American Optical Corporation, Southbridge, Massachusetts 01550 and R.H. Bartram, Physics Department
iv
ABSTRACTS OF PAPERS TO APPEAR IN and Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06268
The observed widths and asymmetries of the spectral lines of Yb3~in phosphate glass are attributed to systematic site-to-site variations in the crystal field at the rare earth. A model rare earth site consisting of a Yb3~ion coordinated by three P0 4 tetrahedra is considered. A cornpliant mo~ieof distortion of the complex is identified, and it is shown that a distribution of distorted sites can lead to lineshapes which reproduce many of the features of the observed spectra. Using a point-ion model, the crystal field at the rare earth site is calculated as a
J.
PHYS. CHEM. SOLIDS
Vol. 8, No. 9
function of a single configuration co-ordinate which describes the distortion. The electrostatic energy of the complex is also determined as a function of the configuration coordinate, and the lineshapes are computed from the crystal—field levels assuming a Boltzmann distribution. Because of uncertainty in the structural parameters of the glass, the effect on the lineshapes of vanations in the dimension of the complex and in the charge states of the ligands is considered. The crystal—field parameters are scaled to compensate deficiencies in the point-ion approximation, and the effect on the lineshapes of changes in the scale factors is discussed. Received 9 February 1970