Fluorescent dyes absorb light energy of a specific wavelength as well as light energy of shorter wavelengths, including ultraviolet (UV) rays and other colors lower in the visible spectrum.
In more detail, fluorescent dyes, unlike conventional pigments, have a unique mechanism for absorbing light. They absorb light at one wavelength, which excites the dye's electrons to a higher energy state. When these electrons return to their ground state, they release energy in the form of light at a longer wavelength. This shift to a longer wavelength is known as the Stokes shift.
Here's a breakdown:
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Visible Light: Fluorescent dyes absorb some portion of the visible spectrum, but they're especially good at absorbing light at the shorter (higher energy) end of the spectrum (e.g., blue or violet light). They then emit light at a longer (lower energy) wavelength (e.g., green, yellow, orange, or red light).
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Ultraviolet (UV) Light: A key characteristic of fluorescent dyes is their ability to absorb UV light. This is particularly important because UV light is invisible to the human eye. When the dye absorbs UV light, it converts this energy into visible light, making the dye appear brighter and more vibrant than it would if it only absorbed visible light.
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Relationship to Color: The specific wavelengths of light that a fluorescent dye absorbs and emits determine its color. The absorption spectrum describes the range of wavelengths the dye absorbs most efficiently, while the emission spectrum describes the range of wavelengths it emits.
Therefore, fluorescent dyes absorb a range of light wavelengths, including visible light and ultraviolet light, and then re-emit light at a longer wavelength within the visible spectrum, leading to their characteristic bright and vibrant appearance.
