Spectroscopy Studies of InP Nanocrystals Synthesized Through a Fast Reaction

We present spectroscopic characterization of InP nanocrystals grown through a fast reaction in a non-coordinating solvent. The photoluminescence (PL) spectra collected from these nanocrystals exhibit a sharp feature associated with the band-edge emission and a broad infrared feature associated with deep level surface trap emission. The emission efficiencies of the as-grown nanocrystals vary between 0.3% and 1% from sample to sample. After undergoing an HF etching process, the emission efficiency increases to 18% and the emission associated with surface states is eliminated from the PL spectrum. Time-resolved photoluminescence (TRPL) experiments conducted at room temperature on the as-grown and HF-etched nanocrystals show that before etching the PL intensity decay is multi-exponential, with a fast (3ns) component independent of wavelength, associated with the non-radiative recombination processes. The etching process effectively eliminates the non-radiative component and the post-etching PL decay can be fitted with a single exponential decay characterized by long (45ns) lifetimes. We tentatively associate these long lifetimes with the recombination of carriers from spin-forbidden states. This assignment is supported by the observation of a significant redshift of the feature associated with band-edge recombination in the PL spectrum with respect to the lowest energy feature in the photoluminescence excitation (PLE) spectrum.