Time-resolved and temperature-dependent photoluminescence of ternary and quaternary nanocrystals of CuInS₂ with ZnS capping and cation exchange

Time-resolved and temperature-dependent photoluminescence (PL) spectroscopy of ternary compound copper indium disulfide (CuInS₂, or CIS) core materials, CIS/ZnS coreshells, and quaternary compound ZnCuInS₂ (ZnCIS) revealed their optical properties with spectral, temporal, and thermal characteristics, which were closely linked to surface-related recombination, and shallow or deep defect-related donor-acceptor transitions. The PL peaks of semiconductor nanocrystals (SNCs) with sizes near Bohr radius displayed at ∼775 nm for CIS, ∼605 nm for CIS/ZnS, and ∼611 nm for ZnCIS. The spectral blue shift and spectral narrowing with CIS/ZnS and ZnCIS are assigned to the increased spatial confinement and surface regularity with the etching of core materials. Both the shorter lifetime at surface-trapped states or interface states and the longer lifetime at intrinsic defect-related states of CIS, CIS/ZnS, and ZnCIS SNCs were widely distributed across the entire PL spectral region. The surface or interface-trapped electrons were thermally active even at low temperatures, but the electrons at intrinsic defect-related states were relatively stable, which was attributable to the strong Coulomb energy between the charge carriers.