Luminescence and Raman spectroscopy on MgB2

From a comparison of luminescence and Raman measurements on MgB2-ceramics, we ascribe the broad and intense background in the Raman spectra to a luminescence from MgB2. We also find that the frequency and linewidth of the E2g mode at 600 cm−1 exhibits a considerable temperature dependence which we discuss in terms of free-carrier induced effects and electron–phonon coupling.