Optically induced second-harmonic generation in CdI2-Cu layered nanocrystals

A large enhancement (up to 0.40 pm V-1) of the second-order optical susceptibility was observed in CdI2-Cu single-layered nanocrystals for the Nd:YAG fundamental laser beam λ = 1.06 μm. The Cu impurity content and nanolayer thickness of the cleaved layers (about several nanometres) play a crucial role in the observed effect. The temperature dependence of the optical second-harmonic generation (SHG) together with its correlation with Raman spectra of low-frequency modes indicate a key role for the UV-induced anharmonic electron-phonon interactions in the observed effect. The maximal output UV-induced SHG was achieved for a Cu content of about 0.5% and at liquid helium temperatures