Fluorescence is the phenomenon in which a substance absorbs light or other electromagnetic radiation and then re-emits it almost immediately at a longer (lower energy) wavelength.
How It Works:
- Absorption: A molecule absorbs a high-energy photon (often ultraviolet light), exciting one of its electrons to a higher energy state.
- Relaxation: The excited electron quickly loses some energy through non-radiative processes (like vibrations).
- Emission: The electron then drops back to a lower energy state, releasing a photon of lower energy (longer wavelength) than the one absorbed.
Key Features:
- The time between absorption and emission is usually very short — on the order of nanoseconds.
- The emitted light is always lower in energy (red-shifted) due to the energy lost during the relaxation phase.
- This shift is known as the Stokes shift.
Applications:
- Biological imaging: Fluorescent dyes and proteins are used to tag cells and molecules.
- Security: Fluorescent inks are used in banknotes and documents.
- Mineralogy: Some minerals fluoresce under UV light, aiding identification.
- Forensics: Detection of bodily fluids or residues.
Fluorescence is a powerful tool in science and technology, offering insight at microscopic levels and enabling various practical applications through its distinctive glowing property.