The linewidths and line positions of 4I15/2
to 4I13/2 absorption transitions of trivalent erbium in
CsCdBr₃ and CaF₂ were measured as a function of temperature from approximately 10 K to
300 K. By comparing the temperature dependence of these transitions with theoretical models
of electron-phonon coupling the primary mechanism involved were determined.
For Er3+ doped CaF₂ the Raman scattering processes dominated the line broadening, although
the single-phonon direct processes were significant enough to drastically alter the values of the
Raman scattering electron-phonon coupling constant. In comparison, the Er³⁺ doped CsCdBr₃
had negligible Raman scattering contributing to the line broadening. This is likely due to the
exceedingly low Debye temperature and consequently low number of phonons, reducing the
likelihood of two-phonon processes relative to single-phonon processes. The results were then
analysed in terms of the bond length with the ligands and compared with other studies showing
that as the bond length gets shorter the electron-phonon coupling constant associated with
Raman scattering is expected to get smaller.
To explain the line shifts in CaF₂:Er³⁺ it is necessary to treat the Debye temperature as a
parameter. This indicates that the phonon modes causing the line shifts are different from those
causing the line broadening, and in most of the cases are vibronic processes rather than Raman
processes. In the case of CsCdBr₃:Er³⁺ there is very little difference between the fits using the
fixed Debye temperature and a varied Debye temperature in over half of the cases examined.
Given the distribution of phonon modes, it is likely that this small difference arises because
combinations of these processes are of similar intensity, meaning that a combination of Raman
and optical phonon modes are likely causing the line shift.
| Identifer | oai:union.ndltd.org:canterbury.ac.nz/oai:ir.canterbury.ac.nz:10092/8557 |
| Date | January 2012 |
| Creators | Reynolds, Adrian John |
| Publisher | University of Canterbury. Physics & Astronomy |
| Source Sets | University of Canterbury |
| Language | English |
| Detected Language | English |
| Type | Electronic thesis or dissertation, Text |
| Rights | Copyright Adrian John Reynolds, http://library.canterbury.ac.nz/thesis/etheses_copyright.shtml |
| Relation | NZCU |
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