The UV-visible absorption bands in the spectra of lanthanoid ions are ' $X$ ' probably because of th

Question

The UV-visible absorption bands in the spectra of lanthanoid ions are ' $X$ ' probably because of the excitation of electrons involving ' $Y$ '. The ' $X$ ' and ' $Y$ ', respectively, are

Professor PC Thomas Classes · Answer

(b) : Many trivalent lanthanoid ions are coloured both in the solid state and in aqueous solutions. Colour of these ions may be attributed to the presence of $f$-electrons. Neither $\mathrm{La}^{3+}$ nor $\mathrm{Lu}^{3+}$ ion shows any colour but the rest do so. However, absorption bands are narrow, probably because of the excitation within $f$-level (orbitals).