title: Near-Unity Internal Quantum Efficiency of Luminescent Silicon Nanocrystals with Ligand Passivation.
abstract: Spectrally resolved photoluminescence (PL) decays were measured for samples of colloidal, ligand-passivated silicon nanocrystals. These samples have PL emission energies with peak positions in the range ∼1.4-1.8 eV and quantum yields of ∼30-70%. Their ensemble PL decays are characterized by a stretched-exponential decay with a dispersion factor of ∼0.8, which changes to an almost monoexponential character at fixed detection energies. The dispersion factors and decay rates for various detection energies were extracted from spectrally resolved curves using a mathematical approach that excluded the effect of homogeneous line width broadening. Since nonradiative recombination would introduce a random lifetime variation, leading to a stretched-exponential decay for an ensemble, we conclude that the observed monoexponential decay in size-selected ensembles signifies negligible nonradiative transitions of a similar strength to the radiative one. This conjecture is further supported as extracted decay rates agree with radiative rates reported in the literature, suggesting 100% internal quantum efficiency over a broad range of emission wavelengths. The apparent differences in the quantum yields can then be explained by a varying fraction of "dark" or blinking nanocrystals.
authors.affiliation: †Materials and Nano Physics Department, ICT School, KTH-Royal Institute of Technology, 16440 Kista, Sweden.
authors.forename: Fatemeh
authors.initials: F
authors.lastname: Sangghaleh
authors.affiliation: †Materials and Nano Physics Department, ICT School, KTH-Royal Institute of Technology, 16440 Kista, Sweden.
authors.forename: Ilya
authors.initials: I
authors.lastname: Sychugov
authors.affiliation: ‡Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada.
authors.forename: Zhenyu
authors.initials: Z
authors.lastname: Yang
authors.affiliation: ‡Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada.
authors.forename: Jonathan G C
authors.initials: JG
authors.lastname: Veinot
authors.affiliation: †Materials and Nano Physics Department, ICT School, KTH-Royal Institute of Technology, 16440 Kista, Sweden.
authors.forename: Jan
authors.initials: J
authors.lastname: Linnros
keywords: dispersion factor; lifetime; nonradiative channel; photoluminescence decay; radiative rate