Anomalous Blue Shift of Exciton Luminescence in Diamond

Generally speaking, for a semiconductor, the temperature dependence of excitonic emission corresponds to that of its band gap. However, an anomalous behavior is exhibited by the excitonic luminescence of diamond where as the temperature increases (from 10 to 300 K), its indirect exciton luminescence peak displays a spectral-distinguishable blue shift, whereas the indirect band-gap absorption shows a weak red shift. According to experimental high-resolution deep-ultraviolet spectra and theoretical analysis, the weak red shift of its indirect band gap is ascribed to its large Debye temperature (Theta(D) approximate to 2220 K), which makes the lattice constant change comparatively little in a large temperature range, so the change of its band gap is relatively small; in this case, as the temperature rises, the thermal population of valence-band holes that moves to a high-energy state far away from the Fermi surface contributes to the macroscopic blue shift of its excitonic emission.

Automated summary

In general, the temperature dependence of excitonic emission in a semiconductor corresponds to its band gap. However, diamond exhibits an anomalous behavior where the indirect exciton luminescence peak undergoes a blue shift while the indirect band-gap absorption shows a weak red shift as the temperature increases. This can be explained by the large Debye temperature of diamond, which results in a relatively small change in its lattice constant and band gap, and the thermal population of valence-band holes contributing to the blue shift of its excitonic emission.