Defect-induced photoluminescence and third-order nonlinear optical response of chemically synthesized chalcopyrite CuInS2 nanoparticles

We report on linear and nonlinear optical properties of chalcopyrite CuInS2 nanoparticles prepared via thermal decomposition of metal complexes. A broad photoluminescence band with a large Stokes shift is observable, and its decay time depends strongly on the emission energies. The photoluminescence is ascribed to radiative recombination of photo-excited carriers after multiple-step hopping among deep trapping sites on nanoparticle surfaces. The imaginary part of the third-order susceptibility exhibits a resonant behaviour at the transition between the lowest quantized levels of conduction and valence bands. The third-order nonlinearity is discussed in terms of the Stark effect due to surface-trapped carriers.