Fluorescence measurements

Under the influence of an external light source, outermost electrons of an atom undergo transition to the first (and possibly higher) energy levels of the material. On returning to the ground level, an electron is emitted with a frequency that corresponds to the difference in energy levels between the concerned quantum states. This frequency is, thus, purely a material property, independent of the wavelength of the incident radiation. Since the laser power required to raise electrons to the higher energy level needs to be necessarily higher, the incident frequency v is greater than the emission at frequency v₁ and scattering can be classified here as inelastic.

Figure 7.9: Energy transitions during fluorescence measurement.