Spectral tuning of colloidal Si nanocrystal luminescence by post-laser irradiation in liquid

We report a simple technique to tune the luminescence spectra of blue-emitting colloidal silicon nanocrystals (Si-ncs) to the ultraviolet region via post-laser irradiation. The post-laser irradiation of the as-prepared colloidal Si-ncs which exhibited a broad photoluminescence (PL) centered at ∼390 nm with a bandwidth of 105 nm caused a spectral peak shift to ∼330 nm and a decrease in the bandwidth to 80 nm. The degree of the spectral tuning can be controlled by changing the irradiated laser power. The spectroscopic and transmittance electron microscopy analysis revealed that this spectral tuning effect is due to the size reduction of Si-ncs by selective absorption of post-irradiated laser light by particular-sized Si-ncs that have bandgap energies resonant with the irradiated photon energy, as well as the resultant ablation of these Si-ncs.