The interaction of electromagnetic radiation with matter

scattering- emission- ABSORPTION- EM SPECTRUM

The transition from a higher level to a lower level if energy is transfered to the radiation field, or nonradiative decay if no radiation is emitted

Emission or luminescence - atoms or molecules that are excited to high energy levels can decay to lower levels by emitting radiation.

Atomic or optical emission - atoms excited by a high-temperature energy source.

Atomic fluorescence - atoms excited.

Molecular fluorescence - electronic states of molecules are excited and decay to lower energy states.

Phosphorescence - similar but the decay is much slower.

An example: fluorescence

The atoms and molecules are excited:

molecules are excited and decay to lower energy states:

scattering- emission- ABSORPTION- EM SPECTRUM

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