Anomalies in the linear absorption, transient absorption, photoluminescence and photoluminescence excitation spectroscopies of colloidal InP quantum dots

We report photoluminescence (PL), linear absorption and femtosecond, transi ent bleaching spectra for a colloidal solution of indium phosphide (InP) qu antum dots (QDs) at ambient temperature. The PL quantum yield is shown to d epend significantly upon the excitation wavelength and the PL excitation sp ectrum deviates markedly from the absorption spectrum. The cooling of elect rons and holes to the lowest energy excited state is determined, by transie nt bleaching spectroscopy, to occur with an efficiency that is independent of the excitation wavelength. These results are discussed in terms of a threshold for a non-radiative dec ay process that resides above the bandgap and a PL quantum yield that depen ds upon the size of QD. (C) 2001 Elsevier Science B.V. All rights reserved.