  We investigate the neutralization of charged defects in a Cu$_2$O crystal
experimentally with a cw two-color pump-probe setup. We demonstrate that the
excitation of high-lying Rydberg excitons at low densities generates an
enhancement of exciton absorption up to a factor of 3. The result is an overall
improvement of the absorption spectrum's quality in terms of increased
oscillator strengths and narrower linewidths, referred to as purification. The
reduction of the amount of charged impurities in the crystal is further
verified by a thorough analysis of impurity photoluminescence signals.
