Introduction:
Ce3+ and Yb3+ are two types of ions that are commonly found in inorganic compounds. Both ions have unique electronic configurations that result in their distinct properties. While they are colorless in their ground state, they exhibit strong absorption in the ultraviolet (UV) region of the electromagnetic spectrum.

Electronic Configurations:
1. Ce3+ Ion:
- The Ce3+ ion is derived from the element cerium (Ce) by losing three electrons. The electronic configuration of Ce3+ is [Xe] 4f1 5d0 6s0.
- The 4f1 electron configuration indicates that there is one electron in the 4f orbital, which is responsible for the absorption of UV light.

2. Yb3+ Ion:
- The Yb3+ ion is derived from the element ytterbium (Yb) by losing three electrons. The electronic configuration of Yb3+ is [Xe] 4f13 5d0 6s0.
- The 4f13 electron configuration indicates that there are thirteen electrons in the 4f orbital, which also contributes to the absorption of UV light.

Colorless Nature:
1. Absence of d-d Transitions:
- Both Ce3+ and Yb3+ ions have empty d orbitals in their electronic configurations.
- Since they lack d-d transitions, which are responsible for the absorption of visible light, they appear colorless to the human eye.

2. Forbidden f-f Transitions:
- The 4f electrons in Ce3+ and Yb3+ ions are shielded by the filled 5s and 5p orbitals.
- This shielding results in weak interactions between the 4f electrons and the external environment, leading to forbidden f-f transitions.
- The absence of visible light absorption due to these forbidden transitions contributes to the colorless nature of Ce3+ and Yb3+ ions.

Strong UV Absorption:
1. f-f Transitions in the UV Region:
- Although Ce3+ and Yb3+ ions do not absorb visible light, they exhibit strong absorption in the UV region.
- The 4f electrons can undergo f-f transitions from one energy level to another, resulting in the absorption of UV light.
- These transitions occur due to the difference in energy levels between the 4f orbitals.

2. Size and Charge Effects:
- The absorption of UV light by Ce3+ and Yb3+ ions can be attributed to their specific electronic configurations and structural properties.
- The size and charge of the ions influence the energy levels and electronic transitions, leading to strong UV absorption.

Conclusion:
Ce3+ and Yb3+ ions are colorless in their ground state due to the absence of d-d transitions and the occurrence of forbidden f-f transitions. However, they exhibit strong absorption in the UV region of the electromagnetic spectrum due to f-f transitions that involve the 4f orbitals. The specific electronic configurations, size, and charge of these ions contribute to their unique absorption properties.