Linear and NLO spectroscopy of GaSe and InSe nanoparticles formed via laser ablation

Nanoparticles of layered GaSe, InSe were fabricated by laser ablation (LA) method (KrF laser, lambda = 248 nm, 50 Hz, maximum energy 200 mJ, tau = 4 ns) and characterized by: center dot XRF; center dot GDOES; center dot SEM and TEM; center dot UV-, VIS-, and IR- absorption; center dot Raman and PL spectroscopy (also in confocal geometry). Results are discussed in relation to the particle size. Absorption spectra of particles with diameter 20 nm and less turned out to be blue shifted and is consisted with a weak confinement effect on Wannier-Mott type excitons. It is shown, that with decreasing the particle size the energy position of the low-frequency Raman active phonons in both compounds are shifted to lower frequencies (21 and 18 cm(-1) in bulk GaSe and InSe and 8 and 7 cm-1 in particles with sizes 5 and 7 nm, respectively). From the low frequency Raman data, decrease of the force constants ca. 25 % (for GaSe) due to the formation of the nanoparticles are estimated, and the origin is suggested. Second harmonic generation (SHG) with 1064 nm line of a mode locked Nd : YAG laser was observed for nanoparticles ablated on different substrates. Potential for using these structures for laser light visualizators are discussed.