Geo,

Pretty much the same thing but with a twist. It occurs with the valance band outer most electrons in atoms, molecules and crystals. In this case it’s a crystal center with an activator element of low concentration. The energy required to get an excited state in the visible 400 to 680 nm range ?is 1.8 to 3.1 eV. That can be by photons, protons and electrons just like XRF but the energy levels are much lower and act on the outer shells. The twist is the crystal center needs an activator element defect to get the energy transfer for fluorescence rather than heating. The emission wavelength can be dependent on the excitation wavelength.

Dud

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