Stimulated emission and optical third-order nonlinearity in Li-doped ZnO nanorods

We report the structure and optical properties of semiconductor Li-doped ZnO nanorods. The sample was synthesized by an ethylenediamine-assisted low-temperature hydrothermal technique. The obtained morphology was studied by using high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction techniques. Our sample exhibits a crystalline Wurtzite phase of ZnO grown along the [101] direction. However, the lattice fringes corresponding to a ZnO sample intercalated with Li ions in the growing direction correspond to 2.58 Å instead of 2.46 Å, which is the reflection [101] for the ZnO hexagonal wurzite phase. The morphology of the rods changes dramatically. In the case of ZnO rods intercalated, we obtained a sharp pencil morphology. Large values of two photon absorption were measured as well as an important photoemission response. Near resonance, the stimulated emission of the sample was measured with picosecond pulses at 355 nm, finding a lasing threshold of around 30 MW/cm ² (780 μJ/cm ²). At this wavelength, the value of β ) 2.4 × 10 ^-4 m/W was measured. Far from resonance, by measuring a self-diffraction effect at 532 nm, we obtained a value of β ) 1 × 10 ^-10 m/W and an important pure electronic nonlinear refraction value n ₂ ) -1 × 10 ^-15 m ²/W.