In Which Your Class Really Shines

White fabrics are sometimes made whiter with a fluorescent dye. Turn on an ultraviolet lamp in a darkened classroom and illuminate people standing at the front of the room. The victims should not look directly at the lamp, because ultraviolet light is harmful to eyes.) You will discover emission from white fabrics, including shirts, pants, shoelaces, and unmentionables. You may also be surprised to see fluorescence from teeth and from recently bruised areas of skin that show no surface damage. 

A fluorescent lamp is a glass tube filled with Hg vapor. The inner walls are coated with a blend of red and green phosphors (luminescent substances). The red phosphor is Eu doped into Y2O3. The green phosphor 

Emission spectra of phosphors scraped from the inside of a compact fluorescent lamp. is selectively excited at 280 nm, and is selectively excited at 240 nm. [C. Degli Esposti and L Bizzochi.y. Chem. Ed. 2008, 85, 839.] 

Fluorescent lamps are more efficient than incandescent lamps in converting electricity into light. In the near future, even more efficient LED (light-emitting diode) lamps will replace fluorescent lamps. Replacing a 75 W incandescent bulb with an 18 W compact fluorescent bulb saves 57 W. Over the 10 000-h lifetime of the fluorescent bulb, you will reduce CO2 emission by -600 kg and will put 10 kg less SO2 into the atmosphere (see Problem 19-22). Alas, fluorescent bulbs contain Hg and should be recycled at a collection center where Hg will be captured from the bulbs. They should not be discarded as ordinary waste. 

Fluorescence emission of a photon from a transition between states with the same spin (e.g.. Si So) Phosphorescence emission of a photon from a transition between states with different spin (e.g., Ti - So) 

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