Exciton energy gap

Silicon carbide 2H-SiC Egx 3.330 4 Excitonic energy gap optical absorption... 

Table 1 Low-Temperature Band Gap Energies (Eg), Exciton Energy Gap (Eg,), and Exciton Binding Energies (Ej) of Various SiC Polytypes...

Figure C2.17.11. Exciton energy as a function of particle size. The Bms fonnula is used to calculate the energy shift of the exciton state as a function of nanocrystal radius, for several different direct-gap semiconductors. These estimates demonstrate the size below which quantum confinement effects become significant.

The picture presented above for confinement of the excitons within the device is for the EM layer sandwiched between the HTL and ETL. The EM need not be a discrete layer in the OLED, however, for exciton confinement to occur. Alternatively, the EM can consist of a luminescent molecule doped (- 1%) into a polymeric or molecular host material (40,41,54,55). So long as the energy gap (or band gap) of the host is higher than that of the EM dopant, excitons will be effectively trapped or confined on the dopant molecules leading to improved EL efficiency. An example of such a dopant-based device... 

Figure 4.12 The energy levels of an exciton. The arrows indicate the possible optical exciton transitions in respect to the energy gap, Eg. E), is the binding energy.

EXAMPLE 4.5 From the absorption spectrum in Figure 4.14, determine (a) the energy gap of CU2O, (b) the reduced effective mass of the exciton, assuming By = 10, and (c) the Bohr radius of the exciton n = 2. 

The combination of a hole polaron and an electron polaron, with binding energies Ep+ and Ep-, respectively, results in the formation of an exciton. Their difference corresponds to Et and is also referred to as the single particle energy gap Egsp -... 

The study of the radiative recombination of excitons makes it possible to investigate the influence of the radiation-stimulated destruction of C60 fullerenes (partially of C70) on changes of the singlet states within the energy gap. It is known that the emission of excitons in this case is the result of the presence of own dimeric traps [11] and X-centers, caused by the chemically bound with fullerenes and intercalated impurities [8], and also of taking into account the corresponding phonon states. 

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