Effect of the surface chemical modification on the optical properties of polymer-stabilized PbS nanoparticles

PbS Nanoparticles in the range 3.8–4.5 nm have been prepared in solution by H2S treatment of a Pb2+- containing copolymer (P-Pb). The variations of the P-Pb molecular weight before and after reacting with H2S implied that there existed some chemical bonds between the surface of the PbS nanoparticles and the copolymer. IR results proved that the chemical bond was Pb—OOC. When the molar ratio (the ratio H2S:Pb2+) was ⩽ 1, there existed Pb—OOC bonds on the particle surface, while most of the Pb—OOC bonds were broken when the molar ratio increased to 2.5:1. Different surface bonding situations are represented by different absorption spectra, the higher the molar ratio, the larger the absorption coefficient. These effects prove that the surface defects relative to the Pb—OOC bonds on the particle surface, can trap the electron–hole pairs effectively and cause a decrease in the absorption coefficient. On the other hand, excess H2S removed the Pb—OOC bonds and saturated the sulfur vacancies on the particle surface, where the radiation combination of the charge carriers occurred. As a result, the laser-induced luminescence bands appearing for the 0.75:1 and 1:1 colloids disappeared completely for the 2.5:1 colloid.