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High Pressure Optical Study of KTbP2Se6

J. L. Burris a, I. Orgzall b, C. R. Evenson c, P. K. Dorhout c,
H. D. Hochheimer a

aDepartment of Physics, Colorado State University, Fort Collins, CO 80523, USA
bHochdrucklabor, Interdisziplinäres Forschungszentrum "Dünne Organische und Biochemische Schichten", Universität Potsdam, Postfach 60 15 53, D-14473 Potsdam, Germany
cDepartment of Chemistry, Colorado State University, Fort Collins, CO 80523, USA

We have observed a pressure induced phase transition in KTbP2Se6 at about 9.2 GPa which was accompanied by a discontinuous jump of the absorption edge of about 0.5 eV into the red. We have proposed that the high pressure phase is due to charge transfer from the selenium to the phosphorous accompanied by the formation of a Se-Se bond. In order to exclude a model which involves a 4f-5d charge transfer in Tb, leading to the intervalence charge transfer from Tb3+P4+ — Tb4+P3+,we have measured the pressure dependence of the luminescence of the crystal field split levels of the Tb-ion . A comparison of the pressure dependence of the luminescence spectra of KTb(MoO4)2 and KTbP2Se6 shows that such a charge transfer does not occur in KTbP2Se6 .

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High Pressure Luminescence Study of KTbP2Se6

H. D. Hochheimer a, J. L. Burris a, I. Orgzall b, C. R. Evenson c,
P. K. Dorhout c

aDepartment of Physics, Colorado State University, Fort Collins, CO 80523, USA
bHochdrucklabor, Interdisziplinäres Forschungszentrum "Dünne Organische und Biochemische Schichten", Universität Potsdam, Postfach 60 15 53, D-14473 Potsdam, Germany
cDepartment of Chemistry, Colorado State University, Fort Collins, CO 80523, USA

The results of a previous high pressure absorption , X-ray diffraction and Raman scattering study indicated a pressure induced phase transition in KTbP2Se6 at about 9.2 GPa which was accompanied by a discontinuous jump of the absorption edge of about 0.5 eV into the red. We have proposed that the high pressure phase is due to charge transfer from the selenium to the phosphorous accompanied by the formation of a Se-Se bond. In order to exclude a model which involves a 4f-5d charge transfer in Tb, leading to the intervalence charge transfer from Tb3+P4+ — Tb4+P3+,we have measured the pressure dependence of the luminescence of the crystal field split levels of the Tb-ion . A comparison of the pressure dependence of the luminescence spectra of KTb(MoO4)2 and KTbP2Se6 shows that such a charge transfer does not occur in KTbP2Se6 .

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Raman Spectroscopy of Conducting Polypyrrole under High Pressure 

J. Mikat 1), I. Orgzall 2), H. D. Hochheimer 3)

      1) Universität Potsdam, Physik kondensierter Materie, Hochdrucklabor, Am Neuen Palais 10, 14469 Potsdam, Germany
2)       Interdisziplinäres Forschungszentrum für Dünne organische und biochemische Schichten, Universität Potsdam, Postfach 601553, 14415 Potsdam, German
3)   Colorado State University, Department of Physics, Fort Collins, CO 80523, USA

 The nature of the charge carriers in conducting polypyrrole highly doped with p-toluenesulphonate and their behavior under pressure was investigated  by high pressure Raman spectroscopy. Changes of band positions and relative intensities of bands assigned to the radical cation (polaron) or the dication (bipolaron) were observed. The results are discussed in the context of structural and electronic aspects by comparing the pressure effects with those observed in the Raman spectrum obtained from oxidized or reduced samples. The changes of the relative number of both charge carrier species indicated in the Raman spectra under pressure are explained by a shift in the character of the dominant charge carriers from bipolarons to polarons.

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High Pressure Brillouin Spectroscopy Using an Angle Dispersive Fabry-Perot Interferometer

K. Koski1, J. Mueller1, H. D. Hochheimer2 and J. L. Yarger1
1 University of Wyoming, Department of Chemistry, Laramie, WY 82071
2 Colorado State University, Department of Physics, Ft. Collins, CO 80523

We report the combination of a high-pressure sample chamber and an angle dispersive Fabry-Perot interferometer allowing the rapid measurement of inelastic light scattering from acoustic phonon modes in liquids and solids under hydrostatic pressure.

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Experimental Determination of Acoustic Velocities and Attenuation in Solids and Liquids at High-Pressure Using Angle-Dispersive Brillouin Spectroscopy

K. Koski1, J. Mueller1, H. D. Hochheimer2 and J. L. Yarger1
1 University of Wyoming, Department of Chemistry, Laramie, WY 82071
2 Colorado State University, Department of Physics, Ft. Collins, CO 80523

We report the combination of a high-pressure sample chamber and a stable, non-scanning, angle dispersive Fabry Perot interferometer allowing the rapid measurement of inelastic light scattering from acoustic phonon modes in solid and liquid samples at high pressure. The primary components of the apparatus are a (i) narrow frequency gas ion laser, (ii) a solid or air-spaced etalon, (iii) a multichannel CCD detector, and (iv) a large volume high pressure cell. The fundamental principle of this spectrometer is based on the angular dispersion of light through an etalon. Where upon, the multiple-order frequency dispersed spectrum can be acquired with an array detector. Typical acquisition times are less than one second using low to moderate laser power.

 

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