Experimental study on two-photon oscillator strength of hydrogenic yellow excitons in Cu2O

Two-photon excitation spectra of photoluminescence of Cu2O are studied at 1.6 K to examine the dependence of the oscillator strength on the principal quantum number, n, of [s-d] excitons. The mixed nature of s- and d-excitons has been confirmed. It has been newly found that the oscillator strength of n≥3 excitons follows the prediction of the hydrogenic model, 1/n3, provided that the [s-d] mixing is taken into account. The maximum mixing has been found for n=3 excitons.