Figure 3
(a) Excitation spectrum of a QD monolayer (black line) and differential absorption spectrum of a QD solution (open circles in an arbitrary scale). The black line indicates the variation of PL intensity at 485 nm from the QD monolayer on 100-nm thick Si3N4/Ag as a function of excitation wavelength. The open circles form a differential absorption spectrum (dA/dλ), which is a measure of density of states (DOS) of QDs as a function of wavelength. The inset is the differential absorption spectrum with a wider wavelength range. (b) Excitation spectra of the samples (QD monolayers on 5-nm, 10-nm, 20-nm, 30-nm, 50-nm and 100-nm thick Si3N4/Ag). All the intensities are re-scaled simultaneously for comparison such that the intensity of QDs on 100-nm thick Si3N4/Ag is adjusted to 1 for the excitation at 379 nm. (c) Re-plot of the PL intensities in (b) by normalizing with the intensity from the QD monolayer on 100-nm thick Si3N4/Ag at all the excitation wavelengths. The same color indicates the same sample in (a–c).
