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Fluorescence & Phosphorescence

  • Introduction
  • Video& Results
  • Materials
  • Procedure
  • Preparation & Notes
  • Download Files

Fluorescencecoffeefilter_eye
Some materials will glow brightly when exposed to UV light.  While the material absorbs the UV light, it emits light of a different color, which has a longer wavelength.  When the UV light is turned off, the glowing stops. This property is called fluorescenceMany common items around us can fluoresce under UV light. Molecules that are fluorescent tend to have ringed structures and mobile electrons. The molecules on this page are quinine (top right), chlorophyll (bottom left) and vitamin B-2/riboflavin (bottom right).

Phosphorescence
If the glowing continues after the UV light is turned off, then the property is called phosphorescence.

Activity
In this activity the students will have a chance to extract chlorophyll from spinach and then examine it’s fluorescence properties.  It glows a bright red under UV light.   Then students will be able to check for fluorescence in a variety of common materials. Students can also crush Vitamin B2 and suspend in water. Riboflavin fluoresces a bright yellow color.

 chlorophyll_glow

riboflavin_glowschlorophyll_structure riboflavin structure

 

 

 

 

 

 

1) Video Demonstration of Extracting Chlorophyll from Spinach

2) Beaker with chlorophyll to a dark room and shine a UV light on it. Voila!

 chlorophyll_glow

 

 

 

 

 

3) Glass with Vitamin B2 solution under a UV Light

riboflavin glow

 

Materials – Fluorescence

UV flashlight with visible filter from teachersource.com (UV-644 $39.95) or less expensive UV sources from Deal Extreme

General Materials

  • mortar & pestle or bowl with grinding implement
  • scissors
  • coffee filters
  • clear cups, jars or beakers for filtering into
  • plexiglass for smearing vaseline onto (optional)

Fluorescent Materials

  • tonic water
  • vitamin B’s - thiamine, niacin and riboflavin (riboflavin is really bright)
  • vaselineb2 bottle
  • highlighter pens
  • laundry detergent
  • toothpaste with whitener

Chlorophyll extraction

  • spinach (for chlorophyll extraction)
  • rubbing alcohol/ethanol(for chlorophyll extraction)
  • coffee filter (for chlorophyll extraction)

Phosphorescence Demonstration


Extraction of chlorophyll

  1. Take 5 or 6 spinach leaves.  Cut into small pieces using scissors, place in a bowl and then grind with spoon, or rock. A mortar and pestle is ideal.
  2. Add a small amount of rubbing alcohol (10 - 20 ml) to the spinach leaves, grind and stir until the color of the liquid changes.
  3. Strain the liquid through a coffee filter into a clear cup or test tube.  You can squeeze the liquid out of the filter or add more rubbing alcohol to get more spinach juice. You should have at least an inch of liquid in the cup. What color is the liquid?
  4. Look at the liquid under a UV light.  Is it fluorescent?  What color is the light that is emitted?

Vitamin B2 - Riboflavin

  1. Take 100 mg Vitamin B-2 tablet (1/4 to 1 tablet is fine) and crush with spoon. Place in a cup. bottle B2
  2. Add approximately 100- 150 ml of water to the crushed vitamin B-2. Crush & mix more.
  3. Strain the liquid through a coffee filter into a cup or test tube. What color is the liquid?
  4. Look at the liquid under a UV light.  Is it fluorescent?  What color is the light that is emitted?

Other fluorescent materials

  1. Pick any of the remaining items and examine under the light.  Which are fluorescent?

Phosphorescence Demonstration

  1. Take the vinyl square coated with phosphorescent dye and run a UV pen light along the surface. The UV pen will leave behind a phosphorescent trail that will last for a minute or two.
  2. Alternately, place a shape, like a hand or a something that will block UV light on the square and shine the UV light at the square. The "Shade" of the shape will maintain the original color of the square while the uncovered portion of the square will be phosphorescent.

Notes
UV absorption and fluorescence emission spectra of chlorophyll (click here) and riboflavin (click here).

References