Question

Provide one example of the interaction between matter and light that you observe around you. Tell us the following about that interaction:

1). What are the bonds or atoms that are excited in this interaction? You might have to guess on this one, but that is all right. Try to at least guess what type of molecules your material consists of.

2). What does the interaction between the photons and materials result in? (There are three de-excitation mechanisms once the atoms in the materials are excited.)

3). Is it possible to obtain longer wavelength photons from the interaction of photons with molecules?  Is that a violation of the conservation of energy?

4). What type of photon did the material interact with?  What energy range is that photon in?

Answer 1

Solution.

The example is the use of colored glasses. The light of some wavelength is being absorbed by a dye which is incorporated into the material of glasses.

1) Absorption of visible light by a dye molecules depends on electron transitions between molecular orbital energy levels, especially delocalized pi-electrons of double bonds. It can be molecules of some triarylmethane dye.

2) The interaction between the photons and materials result in the absorption of light of some wavelength and transmittance of another particular wavelength. The probable photochemical events are absorption of visible light to give dye molecules in the first excited singlet state. The internal conversion and de-excitation to a ground state will be afterwards.

3) The excited electrons in atoms and molecules can interact with energy lowering before they can make a downward transition. In that case, they emit a photon of lower energy and longer wavelength (fluorescence). It is not a violation of the conservation of energy because the emitted photon has a lower energy.

4) The synthetic organic dye interacts with the photons of visible light. The range of photon energies for visible light from red to violet is 1.63 to 3.26 eV, respectively.