Fluorescent material works by absorbing light energy and then re-emitting it as light of a different color.
Understanding Fluorescence
At its core, fluorescence is a phenomenon where a substance (called a fluorophore or fluorescent material) temporarily absorbs electromagnetic radiation (like light) and then re-emits it. This re-emitted light is what we perceive as fluorescence.
According to the reference, a molecule can absorb a photon of light and therefore its energy, and then reemit a photon of lower energy and higher wavelength. The emitted light is fluorescence or fluorescent light.
The Process in Simple Steps
Here's a breakdown of how this happens:
- Absorption: A photon of light strikes a molecule in the fluorescent material.
- Energy Gain: The molecule absorbs the photon's energy. This excites the molecule, moving it to a higher energy state.
- Energy Loss (Briefly): Before re-emitting light, the molecule typically loses a small amount of energy, often as heat through vibrations.
- Emission: The molecule returns to its ground state (lower energy level) by re-emitting a photon.
- Fluorescent Light: This emitted photon is the fluorescent light we see. Crucially, because some energy was lost before emission, the emitted photon has lower energy and a higher wavelength compared to the absorbed photon.
Why Lower Energy and Higher Wavelength?
The relationship between energy and wavelength is inverse: higher energy corresponds to lower wavelength (like UV or blue light), and lower energy corresponds to higher wavelength (like green, yellow, or red light).
- When the fluorescent molecule absorbs light, it takes in a photon of a specific energy (often high energy, e.g., UV or blue).
- It loses a little energy internally (non-radiative decay).
- When it emits light, it releases a photon with less energy than it initially absorbed.
- This lower energy photon corresponds to a longer wavelength, meaning the emitted fluorescent light is shifted towards the red end of the spectrum compared to the light that was absorbed.
This difference in wavelength between absorbed and emitted light is known as the Stokes shift.
Practical Examples
Fluorescence is used in many applications:
- Fluorescent Lights: Phosphors inside the tube absorb UV light produced by mercury vapor and emit visible light.
- Highlighters: Ink contains fluorescent dyes that absorb UV/violet light and re-emit it as bright visible colors.
- Security Features: Banknotes and documents often have fluorescent markings visible only under UV light.
- Scientific Research: Fluorescent markers are used to tag molecules and structures for imaging.
In essence, fluorescent materials act like tiny energy converters, taking in light of one kind and giving off light of another, typically less energetic, kind.
