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what are emission and absorption
Absorption and emission are often used as characteristics that help identify substances.They are the core properties of molecules which make them useful. Materials can be designed that absorb light at one wavelength and emit it at another. Specific colors need to be matched to the application that the materials are intended for.
Emission spectra are produced by thin gases in which the atoms do not experience many collisions (because of the low density). The emission lines correspond to photons of discrete energies that are emitted when excited atomic states in the gas make transitions back to lower-lying levels.
An absorption spectrum occurs when light passes through a cold, dilute gas and atoms in the gas absorb at characteristic frequencies; since the re-emitted light is unlikely to be emitted in the same direction as the absorbed photon, this gives rise to dark lines (absence of light) in the spectrum.


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