Hot‐exciton luminescence in CdSe crystals

Abstract

AbstractThe emission spectra of CdSe crystals under the excitation in the region of fundamental absorption with the HeNe laser line λ = 6328 Å have been studied at temperatures 4.2 to 300 °K. A set of narrow emission lines shifted by the energies of an integer number of LO phonons to lower energies from the exciting line has been observed in the region of fundamental absorption. No emission line has been observed at the position shifted by l LO. The intensity of LO‐shifted lines drastically decreases with increasing crystal temperature. It is shown that this temperature dependence and the comparable intensity of multiphonon lines cannot be explained on the basis of a resonant Raman scattering model. The observed line emission was assigned to a luminescence of hot excitons. The latter model can explain both thermal quenching of emission and intensity distribution in the spectrum. In the emission spectra of mechanically polished samples a defect activated 1 LO emission line has been observed. This line is due to the indirect exciton transitions without phonon participation in the partially disordered surface layer. Besides the line structure, the continuous emission background has been observed in the region of fundamental absorption. This background forms the high energy exponential tail of the quasi‐equilibrium exciton emission line n = 1 A and can be considered as Urbach region of the exciton emission spectrum.