Optical nonlinearity of a proposed quantum-confined semiconductor colloid

Optical saturation and degenerate four-wave mixing were observed in a bismuth tri-iodide (BiI3) colloid, which has been reported to exhibit quantum confinement effects. A third-order optical nonlinearity ‖χ(3)eff‖=1.4×10−10 esu was measured at 364 nm with ∼500 ps pulses. The temporal decay of the nonlinear mixing signal is slow (>6 ns) and shows acoustic oscillations. All results were found to be consistent with the formation of tri-iodide ions I−3 only, and the effects could be explained by photochemical dissociation. The four-wave mixing signal is thermal in origin.