Femtosecond pulse excited two-photon photoluminescence and second harmonic generation in ZnO nanowires

With femtosecond pulse excitation at the wavelength near 800 nm, we observed three upconverted emission peaks from ZnO nanowires. The ultraviolet peak at about 385 nm and the green emission band centered at about 515 nm were attributed to the near band edge emission and defect level emission, respectively, while the intermediate peak was assigned to the second harmonic generation. From the quadratic dependence of the emission intensity on the excitation pulse energy, it is confirmed that the 385 nm photoluminescence was mainly generated via two-photon absorption in ZnO nanowires under very intense light-matter interaction.