Excitation and relaxation of bound excitons in Cu2O single crystal

Excitation and relaxation processes of photoluminescence from bound excitons were studied in (100) Cu₂O single crystal under irradiation of the wavelength-tunable laser in the 10–300 K temperature range. PL emission bands at 1.72 eV, 1.53 eV and 1.36 eV, assigned to bound excitons localized at oxygen and copper vacancies $V_O^{2+}$, $V_O^{+}$, $V_{\text{Cu}}$, correspondingly, are excited in the energy range 2.9–1.8 eV, covering regions of violet, blue, green and yellow excitons and a red band at 1.93 eV, assigned to the direct excitation of oxygen-vacancy-bound exciton. PL thermal decay curves have a non-monotonous character with signs of negative thermal quenching implying a complex process of bound exciton transfer between defect centres. For all bound exciton emission bands the obtained activation energies demonstrate dependence on excitation photon energy. The excitation energy dependence of the activation energy mirrors that of the PL intensity, suggesting a link between exciton density and thermal stability.