Excitation of rare earth emission in chalcogenide glasses by broadband Urbach edge absorption

Studies of photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy in rare earth (RE)-doped chalcogenide glasses have shown that there are interactions between the fundamental optical absorption and emission processes of the chalcogenide host glasses such as Ge33As12Se55 and the spectrally overlapping intra 4f-shell transitions of Er, Pr and Dy dopants. A broad (∼0.5 eV fwhm), near-band edge PLE band is observed in the excitation spectra of RE emission bands in chalcogenide glasses, superimposed on the expected 4f-RE PLE peaks. The results reviewed here demonstrate that the broad band PLE of the RE emission is due to the absorption of light in the Urbach edge of the host glass followed by non-radiative transfer of the excitation energy to the RE emitters. On the basis of several unique properties of the broad band PLE, we suggest a model for the energy transfer process from the host glass to the REs mediated by intrinsic defect states in the glass.