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Features Take a deeper look at the emerging trends and key issues within the global scientific community. News Stay informed about the latest developments that affect scientists in all parts of the world. Research updates Keep track of the most exciting research breakthroughs and technology innovations. Latest Explore all the latest news and information on Physics World. Cho (ed.), Excitons, Topics in Current Physics, Vol. Hanamura, Excitonic Processes in Solids, Springer-Verlag, Heidelberg (1986). Lyons, Organic Semiconductors, John Wiley and Sons, New York (1967). Birks, Photophysics of Aromatic Molecules, Wiley Interscience, London (1970).į. Whitfield, eds.), Oliver and Boyd, London (1962), pp. Landsberg (ed.), Solid State Theory: Methods and Applications, John Wiley and Sons, London (1969). Walecka, Quantum Theory of Many-Particle Systems, McGraw-Hill, New York (1971). Taylor, A Quantum Approach to the Solid State, Prentice Hall, Englewood Cliffs and New York (1970).Ī. Haken, Quantum Field Theory of Solids, North-Holland, Amsterdam (1976). Davydov, Theory of Molecular Excitons, Plenum, New York (1971). Walmsley, Excitons in Molecular Crystals, W. Weissberger, eds.), Interscience, New York (1967), pp. Jortner, in: Physics and Chemistry of the Organic Solid State (D. Dimmock, in: Semiconductors and Semimetals (R. Whitfield, eds.), Oliver and Boyd, Edinburgh and London (1962), pp. Ehrenreich, eds.), Excitons, John Wiley and Sons, New York (1965). This process is experimental and the keywords may be updated as the learning algorithm improves. These keywords were added by machine and not by the authors. Because of the attractive Coulomb interaction between the electron and the hole in an exciton, the internal exciton states are analogous to those of a hydrogen atom, and some of the lower energy states lie below the conduction band by an energy equivalent to the exciton binding energy in that state. While the pseudomomentum enables an exciton to move throughout a crystal, the relative momentum determines its internal structure. 
An exciton carries a crystal pseudomomentum equivalent to the vector sum of the individual momenta of the electron and the hole and their relative momentum. Such a bound system of a pair of charge carriers is called an exciton. The attractive Coulomb interaction between the excited electron and the hole thus created binds them together to form a bound neutral compound system of the two charge carriers such as a hydrogen atom. In crystals of insulators and semiconductors, when an incident photon is absorbed exciting an electron from the valence to the conduction band, a positive charged vacancy, called a hole, is created in the valence band.
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