Demos: 8A-02 Fluorescence and Phosphorescence

A variety of materials is examined under black light to show the various colors resulting from fluorescence and/or phosphorescence.

Directions: NOTE: You should wear some kind of protective glasses to help block the UV rays entering your eyes. A number of materials is available; among them: colored chalk, various papers, soap powder, liquids in vials and a phosphorescent (glow in the dark) plastic cord. Clothing on yourself, as well as that of students will also glow. First, show the materials in ordinary light. Then darken the room and hold the various objects under the black light.

Suggestions for Presentation: This is a very entertaining, as well as informative, demonstration. For example, the colored chalk can be used to draw lines on your face and even on your teeth. Then turn the blacklight toward your face (see warning above). Bad joke warning: Pull an ordinary handkerchief from your pocket. It will likely fluoresce very brightly. Look at the handkerchief and say, “This handkerchief looks clean, but IT’S SNOT!”

In showing the soap powder, point out that manufactures include fluorescing dyes in the detergents to make whites “whiter than white.” Sunlight and some other sources contain UV light and will cause the dyes to fluoresce.

Many ordinary office papers, because of the chemicals used, will fluoresce quite brightly. Others will not. Show the papers first in white light, then blacklight. The effect is dramatic.

The plastic rope will continue to glow after the blacklight is turned off. This is phosphorescence and is simply fluorescence with a longer decay time. The “phosphors” on a TV screen probably should be termed “fluorescers” since the decay time is almost instantaneous.

Applications: Fabric dyes, laundry detergents, TV phosphors, colored markers (especially highlighters)

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Last Updated: May 9, 2016 11:44 AM