From NIR to Visible Emitting Quantum Dots by Cation Exchange

Roberto Comparelli^a, Maria Lucia Curri^a, Enrico Binetti^a, Marinella Striccoli^a, Michela Corricelli^a^,^e, Teresa Sibillano^b, Cinzia Giannini^b, Rosaria Brescia^c, Andrea Falqui^c, Raffaele Tommasi^d^,^a, Angela Agostiano^e^,^a

^aCNR IPCF, c/o Dept. of Chemistry, University of Bari, Via Orabona 4, Bari, 70126, Italy

^bCNR- IC, Via Amendola 122/O, 70126 Bari, Italy

^cIstituto Italiano di Tecnologia IIT - Nanochemistry Department

^dDepartment of Basic Medical Sciences, Neuroscience and Sense Organs, University of Bari Aldo Moro, Piazza G. Cesare 11, 70124 Bari, Italy

^eDepartment of Chemistry, University of Bari Aldo Moro, Via Orabona 4, 70126 Bari, Italy

Materials for Sustainable Development Conference (MATSUS)
Proceedings of nanoGe September Meeting 2015 (NFM15)

Santiago de Compostela, Spain, 2015 September 6th - 15th

Poster, Michela Corricelli, 037
Publication date: 8th June 2015

Semiconductor colloidal quantum dots (QDs), with optical stability in time and intense, narrow emission in the border region between red and NIR, are of great interest for optoelectronic and bio-imaging applications. However, while the largest quantum dots based on cadmium chalcogenides efficiently emit up to 650 nm, the smallest lead chalcogenides start to emit above 850 nm, leaving uncovered the wavelength window between these values. Furthermore, lead chalcogenides QDs result highly instable under ambient conditions, due to destructive and irreversible oxidative processes occurring at the QD surface.The growth of an inorganic passivation layer on QD surfaces is a common strategy to improve their stability and their photoluminescence quantum yield. Here cation exchange approach has been used to promote the growth of CdS passivation layer on the surface of very small PbS QDs in order to obtain luminescent and stable nanostructures emitting in the range of 700-850 nm. Structural, morphological and compositional investigation (XRPD, TEM, HR-TEM, STEM-EDS) has confirmed a QD size contraction after the cation-exchange process, while the PbS rock-salt crystalline phase is retained. Due to the very small size of starting PbS QDs, the presence of a pure CdS shell as well the composition and the crystalline phase of the surface have been not fully elucidated. Nevertheless, the synthetic strategy results in highly luminescent QDs emitting in the expected spectral range. Absorption and photoluminescence spectroscopy are compatible with the growth of a passivation layer at expenses of PbS core, as inferred by the blue-shift of the excitonic peaks. The surface passivation induces a strong enhancement of the PL emission and a considerable increase of the excited state lifetime. Moreover the QDs show an increased stability against oxidation in time. Thanks to their absorption and emission spectral range and the slow recombination dynamics, such small and highly luminescent QDs can find interesting application in photovoltaics as well as in optoelectronic emitting devices.

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