Changing Colors
Aishani Ghosh
Award: Top 100
School: massachusetts academy of math and science at wpi
Teacher: maureen chase
Category: Contrived
Photo #21311
Changing Colors
The image shows a red, 650 nanometer wavelength laser shining into a vial. In the vial, two
chemicals interact to convert the red light from the laser into blue, 470 nanometer wavelength
light. By absorbing the initial red light, the first chemical (sensitizer) reaches an excited state. It
passes this energy to the second chemical molecule (annihilator) which reaches an excited state
as well. Two excited annihilator molecules collide to pass one's energy onto the other. This
second annihilator molecule now has about double the energy. When it returns to its ground state
from the excited state, it releases a photon with approximately double the energy as absorbed
from the initial photon. This process is called Triplet Triplet Annihilation Upconversion
(TTA-UC) and is used to upconvert low energy light into high energy light!
Most people would think of upconverting light as part of chemistry, but it also has a lot of
applications in physics. The wavelength of light decides its color, for example 650 nanometers is
red and 470 nanometers is blue as in the picture. This shows how light behaves as a wave.
However, the annihilator molecules release a photon. A photon is a particle, like a packet of
light, that is massless but has momentum. This shows how light behaves as a particle. In total,
light isn't only a wave or a particle, but has behaviors of both, which is why we say light has
wave-particle duality. In all, TTA-UC teaches us a lot about light in physics!
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