Essential Question of the Day
?
What is “Fluorescence”?
Answer:
A phenomenon in which a
material absorbs one
wavelength of EM radiation
and gives off another.
Examples of Fluorescence:
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White paper is treated with fluorescent compounds to
make it appear brighter. Historical documents that have
been forged can sometimes be detected by placing them
under a black light to see if they fluoresce; fluorescents
have only been used in paper made after about 1950.
Club soda or tonic water contains quinine, a bittertasting fluorescent compound that glows blue-white
under a black light.
Vitamins (specifically vitamin A, thiamine, niacin, and
riboflavin) fluorescent strongly. A small piece of a
vitamin B-12 tablet crushed and dissolved in vinegar
glows a bright yellow under UV light.
Chlorophyll fluoresces with a blood red color. Grind
spinach or Swiss Chard with ethanol and filter the
resulting chlorophyll extract. Bright white light can be
used to drive the fluorescence. Place the extract in a
petri dish on top of an overhead projector lamp in a
darkened room to get the full effect.
Many biological fluids contain fluorescent molecules.
Forensic scientists use UV lights on crime scenes to
detect fluorescence from blood, urine, or semen. Some
marine organisms (notably jellyfish) produce proteins
that are very intensely fluorescent.
Antifreeze fluid contains additives that fluorescent.
Investigators sometimes use black lights to look for
antifreeze splashes on pavement and vehicles to
reconstruct automobile accident scenes.
Laundry detergents contain fluorescent molecules to
make the whites "whiter than white". Detergent residues
on white clothing causes it to glow blue-white under a
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black light. These fluorescents sometimes make white
clothing appear blue in color photographs.
Dental enamel and whiteners also contain fluorescent
compounds that fill in the blue part of the spectrum to
prevent the enamel from appearing too yellow.
Postage stamps are printed with inks that contain
fluorescent dyes.
Some common minerals and gemstones fluorescent,
including gypsum, talc, opal, agate, quartz, and amber.
Fluorescence Light Bulbs