Light from Plastics' How does it work

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Light from Plastics. How does it work?
FACHGEBIET THEORETISCHE PHYSIK I

• by Wichard J. D. Beenken

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Inorganic LED torches
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Materials used in LED torches

• Plastic
• Insulator (10-8 ?-1 m-1)
• Metal
• Conductor (108 ?-1 m-1)
• LED GaAs(P)
• Semiconductor (1 ?-1 m-1)

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Can one use only plastics for all parts of the
torch?
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Periodic system
He
H
C
Ne
F
O
N
B
Be
Li
P
Ar
Cl
S
Si
Al
Mg
Na
Kr
Br
Se
As
Ge
Ga
Ca
K
Sn
Xe
I
Te
Sb
In
Sr
Rb
Rn
At
Po
Bi
Pb
Tl
Ba
Cs
Insulators
Metals
Semiconductors
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Carbon
Diamond
C
Graphite
and a lot of carbon black
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Carbon

C



four valence electrons
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Carbon
Diamond
Four bonds

• insulator
• transparent
• extrem hard
• expensive

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Diamond
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Diamond
Four bonds
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Polyethylene
Four bonds
two hydrogen

• insulator
• transparent
• thermoplastic
• cheap

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Polyethylene

• Synthesis

H
H
H
H
Ethylene
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Polyethylene

• Synthesis

H
H
R
H
H
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Polyethylene

• Synthesis

H
H
R
H
H
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Polyethylene

• Synthesis

H
H
H
H
R
H
H
H
H
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Carbon
Graphite
Three bonds
one free electron

• conductor
• grey-metalic
• smearing

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• Graphite

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Graphite
Three bonds
one free electron
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Polyacetylene
Three bonds
one free electron
one hydrogen

• semiconductor
• silver colored
• plastic
• nobel prize

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The Nobel Prize in Chemistry 2000
Alan J. Heeger
Alan G. MacDiarmid
Hideki Shirakawa
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Polyacetylene
Why is it only semiconducting ?
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Polyacetylene
Nuclei can be displaced...
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Polyacetylene
Nuclei can be displaced...
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Polyacetylene
Nuclei can be displaced...
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Polyacetylene
... forming double-bonds.
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Polyacetylene
Double-bonds are insulating!
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Polyacetylene
conducting
Energy gap
insulating
insulating
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Polyacetylene
H
H
H
H
H
H
H
H
H
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Polyacetylene
H
H
H
H
H
H
H
H
H
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Polyacetylene
H
H
H
H
H
H
H
H
H
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Polyacetylene
H
H
H
H
H
H
H
H
H
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Polyacetylene
H
H
H
H
H
H
H
H
H
Double- and single-bonds are exchanged Electron
has moved to the other terminus Soliton has
propagated with electron
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Polyacetylene

• Energy gap for conduction
• Vibrations can overcome energy gap
• Heat provides vibrations
• Conductivity increases with temperatur
• Semiconductor

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Polyacetylene

• Semiconductor
• Wires (103 107 W-1 m-1)
• Doping
• Diodes, Transistors, etc.
• Light emission
• other conjugated polymers for LEDs

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Graphite
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trans -Polyacetylene
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cis -Polyacetylene
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cis -Polyacetylene
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Polythiophene
Sulfurs enforce additional displacements and fix
the positions of the double-bonds
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Polythiophene
S
S
S
S
S
H
H
H
H
H
H
H
H
H
H
S
S
S
S
S
H
H
H
H
H
H
H
H
H
H
corresponds to light with ? 620 nm (red)
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Polythiophene
S
S
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Polythiophene
S
S
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Polythiophene
S
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Polythiophene
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Polythiophene
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Polythiophene
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Polythiophene
Licht
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Polythiophene
S
S
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• Polythiophene LED