New Lamps for Old: How LEDs are Revolutionizing Lighting Applications

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New Lamps for Old How LEDs are Revolutionizing
Lighting Applications
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New Lamps for Old
Light Emitting Diode
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• Lighting applications presently consume
  about 20 of all electricity generated worldwide.

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Getting Started

• What is light?
• What kind of light can we see?
• How is light produced?
• How does an incandescent light bulb work?

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Light Spectrum
Infrared Radiation
Ultraviolet Radiation
Visible Spectrum
700 nm 1.8 eV
400 nm 3.0 eV
high energy low energy
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1/3 mm
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The gap energy (Eg) is the key!
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Emission of Light from a Semiconductor
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Semiconductors
Similar shading indicates complementary pairs
that preserve the total valence electron count
for AZ stoichiometry.
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Band Gap and Periodic Properties
Element
E
, eV
(
?
, nm)
g
C
5.5
(230)
Si
1.1
(1100)
Ge
0.66
(1900)
?
-Sn
lt 0.1
(12,000)
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Semiconductors
Similar shading indicates complementary pairs
that preserve the total valence electron count
for AZ stoichiometry.
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Band Gap and Periodic Properties
Material
(
, nm)
E
, eV
?
g
(1900)
Ge
0.66
GaAs
(890)
1.42
ZnSe
(460)
2.70
CuBr
(430)
2.91
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LEDs and Color
electrons held tightly
P
Ga
electrons held loosely
As
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LEDs from Red to Green
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Solid Solutions
A
Z
A
Z
A
Z
A
Z
A
Z
A
Z
0.0
1.0
0.2
0.8
0.4
0.6
0.6
0.4
0.8
0.2
1.0
0.0
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Periodic Properties Review

• Atomic size
• As the size of atoms increases, the electrons
  are held more or less tightly?
•  
• Electronegativity is defined as the pull or
  attraction for electrons in a bond.
• From left to right across the periodic table, the
  electronegativity of atoms ______________.
• From top to bottom down a group of the periodic
  table, the electronegativity of atoms
  ______________.
• Arrange the following bonds in order of
  increasing difference in electronegativity?
  GaN GaAs GaP

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Making Observations and Measurements
Measured voltage
Color emitted
Observations with liquid nitrogen dipping
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Acknowledgments

• Hope College
• Lawrence University
• Appleton Area School District
• NSF-MRSEC
• Karen Nordell Pearson
• Arthur Ellis
• George Lisensky
• Mike Condren
• Connie Roop
• Brian Bartel

http//www.mrsec.wisc.edu/nano