Luminescence in the Band Scheme

With small dimensions of the forbidden band the electron transfer of the impurity or of the main substance to the conduction band may take place. The most important luminescent minerals of this kind are ZnS and silver bromides. With the interband spacing of 3-4 eV a UV irradiation with a wavelength of less than 300 nm has enough energy to detach electrons and transfer them from the filled valence band into an empty conduction 

Luminescence generation through direct recombination of electrons from a trap with an activator (tunneling) or with a hole in the valence band (Fig. 2.6c)  

Stimulated release from an electron from the trap to the collection band, followed by emissive recombination with an activator. This process is called thermoluminescence (electron release stimulated by heating) and optically stimulated luminescence (electron release stimulated by light) (Fig. 2.6d) Extrinsic luminescence, where after being excited, electrons of defect ions recombine with the ground state with luminescence emission (Fig. 2.6e)  

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