Question

Why do the lanthanide ions gives rise to sharp bands in their electronic spectra?

Answer 1

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Here is the answer

The 4f electrons of lanthanides yield three types of transitions: (i) Internal 4f-4f transitions which give rise to sharp, narrow bands of comparatively weak intensities which are Laporte forbidden. (ii) Allowed 4fn−4fn-1 (n – l)d, which are relatively broad and intense. (iii) Broad and often intense 4fn−λ−1 fn+1 electron transfer bands generally occurring in the ultraviolet region (λ− represents a hole in the orbital concentratedmainly on the ligands).


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Answer 2

The 4f electrons of the lanthanides yield three types of transitions:

(i) The Internal 4f-4f transitions which give rise to a sharp, narrow bands of the comparatively weak intensities which are generally Laporte

for-bidden.

(ii) this allowed the 4fn−4fn-1 (n – l)d, which are relatively more broad &  intense.

(iii) Broad &  often intense  4fn−λ−1 fn+1 electron transfer, the bands generally occurring in ultraviolet region (λ− represents the hole in orbital concentrated mainly on ligands).

• Spectra of the lanthanides differs from transition metal complex. The spectra of lanthanides complex are the generally more sharper than that of the transition metal complex.
• The f-orbitals are present in the deep n-2 energy shell.

• Thus, influence of the ligand field isn't observed for the lanthanides. However,  transition metal ion's are susceptible for the ligand field effect.
• Thus, the more relaxation time is present for the lanthanides metal complex.

Hence, spectra is sharper for the lanthanides metal complex.

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