II-VI semiconductor nanoparticles formed by Langmuir-Blodgett film technique: Optical study

CdS nanoparticles formed within Langmuir-Blodgett (LB) films of stearic acid and calix[8]arene were studied with different optical methods including surface plasmon resonance (SPR), ellipsometry, UV-visible absorption and fluorescence spectroscopy. For the first time, the process of formation of CdS nano-particles within LB films was monitored in-situ with SPR. The results of ellipsometry, SPR and UV-vis absorption spectroscopy were analysed to evaluate simultaneously the thickness, refractive index and extinction coefficient of LB films. It was shown that all three parameters increase as a result of formation of CdS nano-particles. Photoluminecsence measurements confirmed directly the blue spectral shift caused by CdS particles formation, a fact previously observed with UV-vis absorption spectroscopy. A large Stock's shift of the luminescence band can be related to the formation of "dark excitons" in the pallet-type CdS nano-clusters.