Synthesis and study of quantum size effect, XRD and IR spectral properties of PbS nanocrystals doped in SiO2 xerogel matrix

PbS nanocrystallites with a diameter smaller than 15 nm have been prepared in a pure silica matrix by sol-gel route. Silica xerogels containing 0.01-3 wt% of PbS were prepared by hydrolysis and polycondensation of methanolic tetramethyl orthosilicate [TMOS, Si(OCH3)(4)] in the presence of ammonium hydroxide (NH4OH) catalyst and lead nitrate Pb(NO3)(2) and subsequent reaction with Na2S to form PbS nanocrystals,These PbS-nanocrystals-doped xerogels were characterised by optical absorption, X-ray diffraction (XRD) and infra-rid spectroscopy (IR). Blue shift in optical absorption threshold indicate that the PbS crystallite size reduced from 16 to 5 nm with a decrease in the PbS wt% from 3 to 0.01. It was found from the XRD studies that weak and broad peaks are obtained because of nanocrystalline state of PbS. The PbS crystallite structure was found to be cubic in the SiO2 matrix by observing the peak positions in the XRD pattern. In the IR spectra, the peaks related to PbS bonds were obtained and they are weak. It was observed that there was no change in peak position related to the SiO2 matrix in the presence of PbS in between the SiO2 network.