I am searching and studying excitons and I confronted with a term named Z3 exciton. What is it? And what is its difference with, for instance Z1 or Z2 exciton?
Z3 or Z1, Z2 excitons are labelled according to the locations of the peaks in the emission spectra of materials. These emission peaks are superimposed on the main band spectra linked to transitions between the conduction and valence bands. The occurrence of the various excitons can be attributed to the properties of the material system, such as the strength of interaction of the exciton with phonon as well as other intrinsic properties that determine the radius of the exciton. The Z3 exciton is interesting as it has been linked to the high third-order nonlinearity due to the presence of a upper doubly degenerate valence subband (in Cucl crystallites). And you can have associated Z3(A) and Z3(B) excitons linked to this type of exciton as well. How these excitons shift with frequency depends on the laser intensity.