Excitation Energy Dependence of Photoluminescence Quantum Yields in Semiconductor Nanomaterials with Varying Dimensionalities

The excitation energy dependence (EED) of the photoluminescence quantum yield (Φ_PL) of semiconductor nanoparticles with varying dimensionalities is reported. Specifically, the EEDs of CdSe quantum dots, CdSe quantum platelets, CdSe quantum belts, and CdTe quantum wires were determined via measurements of individual Φ_PL values and photoluminescence efficiency (PL_Eff(E)) spectra. There is a general trend of overall decreasing efficiency for radiative recombination with increasing excitation energy. In addition, there are often local minima in the PL_Eff(E) spectra that are most often at energies between quantum-confinement transitions. The average PL lifetimes of the samples do not depend on the excitation energy, suggesting that the EED of Φ_PL arises from charge carrier trapping that competes efficiently with intraband carrier relaxation to the band edge. The local minima in the PL_Eff(E) spectra are attributed to excitation into optically coupled states that results in the loss of carriers in the semiconductor. The EED data suggest that the PL_Eff(E) spectra depend on the sample synthesis, preparation, surface passivation, and environment.