PbS/polymer nanocomposite optical materials with high refractive index

High refractive index nano-PbS/polymer composites were fabricated from reactive lead-containing precursors and polythiourethane (PTU) oligomer terminated with isocyanate group, followed by in situ gas/solid reaction. The lead-containing precursor with a chemical formula of Pb(SCH2CH2OH)(2) was synthesized in water phase at pH = 5-9 and exhibited an absorption at 317 nm in dimethyl sulfoxide (DMSO) in UV-vis spectra. PbS nanoparticles can be formed in DMSO after treatment with H2S. TEM studies indicated that the PbS nanoparticles were smaller than 10 nm and aggregated seriously in DMSO. After the precursors were incorporated into PTU oligomer, the obtained composite films were treated with H2S to obtain PbS nanoparticles/PTU nanocomposite films. TEM showed that the nanocomposites exhibited interesting phase behaviors depending on the precursor content in films. A uniform spherical aggregate of PbS nanoparticles (nanospheres) with a size smaller than 100 nm formed in the nanocomposite films below 26.3 wt % of lead-containing precursors. When the precursor content was larger than 59.3 wt %, the PbS nanoparticles about 3 nm dispersed uniformly in the whole polymer matrix. Ellipsometric measurement indicated that the precursors/PTU composite films before being treated with H,S had a refractive index in the range 1.57-1.665 and after reaction with H2S, the obtained PbS/PTU nanocomposite films had a higher refractive index in the range 1.57-2.06 with the varied content of precursors from 0 to 67 wt %.