UV fluorescence occurs when certain materials absorb ultraviolet (UV) light and then re-emit that energy as visible light. This process makes the material appear to "glow" under UV light.
Here's a breakdown of the process:
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Absorption of UV Light: Ultraviolet (UV) light, which is invisible to the human eye because its wavelengths are shorter than those of visible light, shines on a fluorescent material. The atoms or molecules within the material then absorb this high-energy UV light.
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Excitation of Electrons: The energy from the absorbed UV light excites electrons within the material's atoms to a higher energy level (an excited state). This excited state is unstable.
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Energy Loss: The excited electron quickly loses some of its energy as heat through molecular vibrations and interactions with other molecules. This energy loss is crucial.
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Emission of Visible Light (Fluorescence): The electron then drops back down to its original, lower energy level (ground state). The energy difference between the excited state (after the initial energy loss) and the ground state is released as a photon of light. Because some energy was lost as heat, the emitted photon has a lower energy and a longer wavelength than the original UV photon. This longer wavelength falls within the visible spectrum, allowing us to see it as colored light.
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Fluorescence is Immediate: The emission of visible light (fluorescence) occurs almost immediately (typically within nanoseconds) after the absorption of UV light. This is a key characteristic that distinguishes fluorescence from phosphorescence.
In Summary:
The material absorbs high-energy, invisible UV light. Electrons jump to a higher energy level, lose some energy as heat, and then fall back down to their original level, releasing the remaining energy as lower-energy, visible light. The color of the emitted light depends on the specific energy difference during this transition.
Example:
- Many minerals fluoresce under UV light. For instance, calcite can fluoresce in a variety of colors, including red, blue, green, and yellow, depending on the presence of trace impurities.