abstract
We studied the light emission of crystalline Si nanoparticles (SiNPs) with hydrogen and native oxide shell terminations using temperature- and time-dependent photoluminescence. We demonstrate that the broad emission normally observed for SiNPs after natural oxidation is in fact formed of two components, which originate from distinct recombination mechanisms that take place simultaneously in the same SiNPs sample. To identify the two spectral components, we exploited the different time scales associated with different emission mechanisms by carefully choosing the measurement time window at which only one of the emission mechanisms is active. Moreover, our experiments indicate that one of the emissions is due to recombination of photogenerated electrons and holes located in the crystalline core of the SiNPs (excitonic emission) whereas the other component originates from donor-acceptor recombination pairs involving states associated with the native oxide shell. These conclusions are supported from experiments carried out with the same SiNPs but where the surface-oxide shell is replaced by H termination. We conclude that both emission components are excited through electronic states of the SiNPs core, pointing out an effective core-to-shell energy/charge transfer. Furthermore, we show that the light emission quantum yield of SiNP ensembles is strongly affected by inter-NP charge transfer and therefore is not determined solely by the properties of the individual NPs. High quantum yields of up to 43%, observed for our surface-oxidized SiNP samples in solution, result from inhibition of inter-NP charge transfer.
keywords
LIGHT-EMITTING DEVICES; HYBRID SOLAR-CELLS; SILICON NANOCRYSTALS; POROUS SILICON; PHOTOLUMINESCENCE PROPERTIES; LUMINESCENCE PROPERTIES; ELECTRONIC-PROPERTIES; VISIBLE SPECTRUM; PLASMA SYNTHESIS; DOTS
subject category
Chemistry; Science & Technology - Other Topics; Materials Science
authors
Botas, AMP; Ferreira, RAS; Pereira, RN; Anthony, RJ; Moura, T; Rowe, DJ; Kortshagen, U
our authors
Alexandre Manuel Pedroso Botas
Post-Doc Fellowship
Maria Rute de Amorim e Sá Ferreira André
Full professor
Groups
G2 - Photonic, Electronic and Magnetic Materials
G3 - Electrochemical Materials, Interfaces and Coatings
Projects
Core-shell and core-host interactions in functional silicon-nanoparticles (PTDC/FIS/112885/2009)
acknowledgements
We acknowledge the financial support from Fundacao para a Ciencia e a Tecnologia (FCT, Portugal), COMPETE and FEDER programs (PTDC/FIS/112885/2009, LA0011/2013/CICECO-FCOMP-01-0124-FEDER-037271, PEst-C/CTM/LA0025/2013 and RECI/FIS-NAN/0183/2012-FCOMP-01-0124-FEDER-027494), and the Danish Council for Strategic Research (THING Project 10-0939691DSF). R.J.A, D.J.R, and U.K. were primarily supported by the MRSEC program of the National Science Foundation (NSF) under award no. DMR-0819885.