Enhancement of persistent photoconductivity by uv excitation in Gd${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{6.3}$

The spectral dependence of the persistent photoconductivity in Gd${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{6.3}$ was measured in the near-infrared to the ultraviolet energy range. The excitation efficiency is strongly enhanced for a photon energy of 4.1 eV. Photons with this energy create electron-hole pairs close to oxygen vacancies in the Cu-O chain layers. Therefore, the probability for the excited electron to be trapped at an oxygen vacancy is very high, which leads to the strong enhancement of the excitation efficiency of persistent photoconductivity.