Excitation wavelength dependence of the photoluminescence quantum yield and decay behavior of CdSe/CdS quantum dot/quantum rods with different aspect ratiosElectronic supplementary information (ESI) available: TEM images of the cores and QDQR series A and B (Fig. S1), decay curves of QDQR series A and B at different λexc (Fig. S2 and S3, respectively), single decay time components obtained from the multi-exponential fits (Table S1) and intensity-averaged decay times of QDQR series A and B at dif

The excitation wavelength ( λ exc ) dependence of the photoluminescence (PL) quantum yield ( Φ PL ) and decay behavior ( τ PL ) 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 exc 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 exc dependence of relative and absolutely measured Φ PL and τ PL 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 PL 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 PL using an integrating sphere setup and Φ PL values measured relative to common Φ PL standards, and underline the need for a correction for particle scattering for QDQRs with high aspect ratios. Our results reveal a strong λ exc -dependence of PL quantum yields and decay times, particularly for longer quantum dot-quantum rods with high aspect ratios.