Excitation wavelength dependence of the photoluminescence quantum yield and decay behavior of CdSe/CdS quantum dot/quantum rods with different aspect ratios

Abstract

The excitation wavelength (λ) dependence of the photoluminescence (PL) quantum yield (Φ) and decay behavior (τ) of a series of CdSe/CdS quantum dot/quantum rods (QDQRs), consisting of the same spherical CdSe core and rod-shaped CdS shells, with aspect ratios ranging from 2 to 20 was characterized. λ between 400-565 nm were chosen to cover the first excitonic absorption band of the CdSe core material, the onset of absorption of the CdS shell, and the region of predominant shell absorption. A strong λ dependence of relative and absolutely measured Φ and τ was found particularly for the longer QDQRs with higher aspect ratios. This is attributed to combined contributions from a length-dependent shell-to-core exciton localization efficiency, an increasing number of defect states within the shell for the longest QDQRs, and probably also the presence of absorbing, yet non-emitting shell material. Although the Φ values of the QDQRs decrease at shorter wavelength, the extremely high extinction coefficients introduced by the shell outweigh this effect, leading to significantly higher brightness values at wavelengths below the absorption onset of the CdS shell compared with direct excitation of the CdSe cores. Moreover, our results present also an interesting example for the comparability of absolutely measured Φ using an integrating sphere setup and Φ values measured relative to common Φ standards, and underline the need for a correction for particle scattering for QDQRs with high aspect ratios.

Influence of Surface Ligands on Charge-Carrier Trapping and Relaxation in Water-Soluble CdSe@CdS Nanorods

“…For a quantitative description of the photoluminescence shape by means of fitting multiple Gaussians, the photoluminescence intensity was further divided by E 3 to obtain lineshape spectra with only little effect on the shape of the photoluminescence spectra [48]. Absolute photoluminescence quantum yields were recorded at an excitation wavelength of 450 nm and 500 nm using a barium sulfate coated integrating sphere [54,87]. The integrating sphere was mounted on the fluorimeter with the entry and output ports of the sphere located in 90 • geometry from each other in the plane of the spectrometer.…”

“…Trends were also recorded in the photoluminescence quantum yield upon excitation at 2.76 eV (450 nm) Φ PL,450 , which was recorded as absolute yields using an integrating sphere as other authors recommended for scattering NR solutions [54]. For TOPO-NR, a moderately high Φ PL,450, =0.58 ± 0.09 was recorded.…”

“…One can get a rough estimate of Φ rad by measuring the photoluminescence quantum yield upon direct CdSe core excitation. We recorded Φ PL upon excitation at 2.48 eV (500 nm), the onset of CdS absorption, in order to record a full CdSe photoluminescence spectrum, and which is already close enough to pure CdSe absorption to potentially see an effect [5,54]. For all samples except PEI-NR, an increase in Φ PL upon excitation at 500 nm was recorded, while for PEI-NR, it remained unchanged ( Table 1).…”

Progress in laser cooling semiconductor nanocrystals and nanostructures

“…Furthermore, polarization sensitivities associated with anisotropic nanostructures as well as potential light scattering effects complicate measurements 87,88 . Finally, solvent light scattering and (possibly) fluorescence contribute to measurement errors 85,89 .…”

On the impact of the laser radiation wavelength and the concentration of quantum dots on the luminescence spectra of colloid solution and QD-doped nanocomposites

“…It follows from the results obtained that the wavelength of the exciting laser has very little effect on the width and position of the luminescence peak center for the sample under the study. However, in [12] the influence of excitation wavelength was observed for quantum rods. Such difference possibly can be explained with QDs structure difference.…”