what is the difference between fluorescence and luminescence background in Raman spectra? What kind of materials give fluorescence background and what kind of materials give luminescence background?
All forms of light being generated from the sample are luminescence. Fluorescence is a specific mechanism to make luminescence and is the most common. In Raman, we often have the annoying background light which could be from fluorescence, or it could be very broad spectrum Raman in amorphous materials or material with weak bonds (Hydrogen or Ven Der Waals) that have been dissolved. Also it could be photo luminescence from an electron going into a valance band of a semiconductor. Often we do not know the actual mechanism that is making the background light and so we just say it is luminescence instead of presuming the mechanism. What things fluoresce? Most things will, but for a material to fluoresce it must be excited with light in a range of colors. One of the major challenges in Raman is to pick your excitation wavelength carefully to avoid exciting the material and causing fluorescence. Attached is an nice article on it by David Tuschel. Also BWTek has some similar material on their web site.
The main difference between fluorescence and luminescence is that luminescence describes any process where photons are emitted without heat being the cause, whereas fluorescence is, in fact, a type of luminescence where a photon is initially absorbed, which causes the atom to be in an excited singlet state.