Nonlinear Optical Properties of PbS Nanocrystals Grown in Polymer Solutions

Lead sulfide nanocrystals were grown in toluene solutions of poly(2-methoxy-5-(2′-ethyl-hexyloxy)- p -phenylene vinylene, polyethylene, poly(1-butene), poly(1-decene), and polystyrene. The PbS nanocrystal diameter was controlled by the polymer used for synthesis and ranged from 4 to 9 nm. Strong nonlinear absorption was observed in open aperture Z-scan measurements of solutions containing the synthesized nanocomposites. The best fit to the experimental data gave high values for β eff in the range of 100−200 cm/GW. The nonlinear absorption of these polymer grown nanocrystals was not observed in nanocrystals grown in polyvinyl alcohol or with oleic acid capping. These differences in nonlinear optical absorption were due to surface chemistry, as the polymer synthesized nanocrystals were free of strongly bonding groups such as surfactant capping or hydroxyl groups. The β eff values in these materials also showed no dependence on nanocrystal size.