Pressure dependence study on the electron–phonon coupling of thulium hexachloroelpasolite Original Research Article

Raman spectra of Cs2NaTmCl6 have been recorded using a diamond anvil cell at ambient temperature. The vibrational energy of each of the Raman-active TmCl6−3 moiety modes increases linearly with pressure. The integrated band areas of the ν1(a1g) and ν2(eg) modes are independent of applied pressure. However, the band area of the ν5(t2g) mode shows an anomalous behaviour, which has been qualitatively interpreted as due to electron–phonon coupling of the aΓ5 electronic state with the Γ1+ν5(t2g) vibronic state. This interaction between the coupled states is strongest between ca. 10 and 13 GPa at ambient temperature. The results serve to emphasize the specificity of the occurrence of strong electron–phonon coupling for particular transitions of a given rare earth ion.