Skip to main content
Chemistry LibreTexts

9.2.4: Electronic Spectra - Ultraviolet and Visible Spectroscopy - Lanthanides and Actinides

  • Page ID
    222269
  • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

    The ions of most lanthanide and actinide ions absorb light in the UV and visible regions.  The transitions involve only a redistribution of electrons within the 4f orbitals (--> f' transitions) are orbitally-forbidden by the quantum mechanical selection rules.  Consequently, the compounds of lanthanide ions are generally pale in color.

    Unlike transition metal complexes, the crystal/ligand field effects for the lanthanide 4f orbitals are virtually insignificant.  This is a result of the extensive shielding of the 4f electrons by the 5s and 5p orbitals.  Consequently the  f --> f' absorption bands are very sharp (useful fingerprinting and quantitation of LnIII)  and the optical spectra are virtually independent of environment.

     lnspec.gif

     

    Figure\(\PageIndex {1}\): The spectrum of a neodymium(III) complex over the range of 25,000 cm-1 to 9100 cm-1 (400 nm to 1100 nm).  The sharp "atom-like" spectral features for Ln3+ ion complexes are the same be thay be in the gas, solid or solution phase. 

    The insensitivity of the f --> f' transitions leads to limited use in study of lanthanide materials.  CeIII and TbIII complexes have the highest intensity bands in the UV due to 4f--> 4fn-15d1 transitions.  The f -->d are not orbitally forbidden (n-1 = 0 (empty sub-shell) for CeIII = 7 (half-filled sub-shell) for TbIII).


    9.2.4: Electronic Spectra - Ultraviolet and Visible Spectroscopy - Lanthanides and Actinides is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.