Question

Which type of transitions are responsible for the colour of lanthanoid cations?

Answer 1

1. The colour of lanthanoid cations is due to electronic transitions within the f-orbitals.
2. Specifically, these are called f-f transitions, where electrons jump between different 4f energy levels.
3. The absorbed light corresponds to visible wavelengths, giving lanthanoids their characteristic colours.
4. Some ions like Ce³⁺, Gd³⁺, and Yb³⁺ are colourless as their absorption occurs outside the visible region.
5. The 4f orbitals are deeply buried and well shielded, causing variations in colour depending on the specific f-f transition energy.

Thus, the f-f electronic transitions are responsible for the colour of lanthanoid cations.