Metal-to-metal charge transfer between dopant and host ions: Photoconductivity of Yb-doped CaF2 and SrF2 crystals
Entity
UAM. Departamento de QuímicaPublisher
American Institute of Physics IncDate
2015-10-14Citation
10.1063/1.4932388
Journal of Chemical Physics 143.14 (2015): 144702
ISSN
0021-9606 (print); 1089-7690 (online)DOI
10.1063/1.4932388Funded by
This work was partly supported by a grant from Ministerio de Economía y Competitividad, Spain (Dirección General de Investigación y Gestión del Plan Nacional de I+D+i, Grant Nos. MAT2011-24586 and MAT2014-54395-P)Project
Gobierno de España. MAT2011-24586; Gobierno de España. MAT2014-54395-PEditor's Version
http://dx.doi.org/10.1063/1.4932388Subjects
Electron transfer; Photoconductivity; Absorption spectra; Excitad states; Doping; QuímicaRights
© 2015 AIP Publishing LLCAbstract
Dopant-to-host electron transfer is calculated using ab initio wavefunction-based embedded cluster methods for Yb/Ca pairs in CaF2 and Yb/Sr pairs in SrF2 crystals to investigate the mechanism of photoconductivity. The results show that, in these crystals, dopant-to-host electron transfer is a two-photon process mediated by the 4fN-15d excited states of Y b2+: these are reached by the first photon excitation; then, they absorb the second photon, which provokes the Y b2+ + Ca2+ (Sr2+) → Y b3+ + Ca+ (Sr+) electron phototransfer. This mechanism applies to all the observed Y b2+ 4f-5d absorption bands with the exception of the first one: Electron transfer cannot occur at the first band wavelengths in CaF2:Y b2+ because the Y b3+-Ca+ states are not reached by the two-photon absorption. In contrast, Yb-to-host electron transfer is possible in SrF2:Y b2+ at the wavelengths of the first 4f-5d absorption band, but the mechanism is different from that described above: first, the two-photon excitation process occurs within the Y b2+ active center, then, non-radiative Yb-to-Sr electron transfer can occur. All of these features allow to interpret consistently available photoconductivity experiments in these materials, including the modulation of the photoconductivity by the absorption spectrum, the differences in photoconductivity thresholds observed in both hosts, and the peculiar photosensitivity observed in the SrF2 host, associated with the lowest 4f-5d band
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Google Scholar:Barandiarán Piedra, Zoila
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Seijo Loché, Luis Ignacio
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