Colloidal indium sulfide quantum dots in water: synthesis and optical properties
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Colloidal indium sulfide quantum dots in water: synthesis and optical properties Mariia V. Ivanchenko, Oleksandra E. Rayevska, Oleksandr L. Stroyuk, and Stepan Ya. Kuchmiy L.V. Pysarzhevsky Institute of Physical Chemistry of National Academy of Sciences of Ukraine, 31 Nauky av., 03028, Kyiv, Ukraine
ABSTRACT Colloidal β-In2S3 quantum dots stabilized in water by a number of polymers or sodium polyphosphate and mercaptoacetate were synthesized. An increase in the stabilizer content was found to result in a decrease in the average dot size from 20–30 to 5–10 nm and formation of a narrow absorption band centered at 290 nm. The position and spectral width of the band were found to be independent on stabilizer concentration, synthesis temperature and molar In:S ratio. The band was assumed to belong to a molecular cluster smaller than 1 nm which is a precursor for formation of larger regular indium sulfide quantum dots. INTRODUCTION Semiconductor nanocrystals smaller than the Bohr exciton diameter 2аВ for a given compound, the so-called quantum dots (QDs), belong to the most intriguing objects of the modern chemistry and find numerous applications in light-emitting devices, luminescent biomarkers, solar cells and photocatalytic systems [1]. Of special interest are the QDs with a large аВ, such as PbS (аВ = 18 nm), PbSe (аВ = 46 nm) [1], In2S3 (аВ > 30 nm) [2], etc. For these semiconductors the exciton becomes spatially confined already in comparatively large particles with the size d of tens of nanometers, while at decreasing d to a few nm we can observe evolution of the electron properties of the semiconductor at extreme exciton confinement. Vigorous research of lead chalcogenide QDs inspired by their unique properties such as IR photoluminescence and the multi-exciton generation phenomenon [1] stimulated progress in synthesis protocols allowing to stabilize PbS and PbSe QDs in various solvents and tailor QD size and surface chemistry. At the same time, the synthetic chemistry of In2S3 QDs, specifically in the form of stable colloids in polar solvents as well as strategies of influencing the average QD size are studied fragmentarily. The present paper reports synthesis of stable aqueous colloids of indium(ІІІ) sulfide using a number of water-soluble polymers and low-molecular-weight agents capable of forming complexes with In(III) such as sodium polyphosphate and mercaptoacetate. For the latter two a detailed study of synthesis conditions on the optical properties of colloidal indium sulfide QDs was performed and means of influencing the In2S3 QD size were found.
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EXPERIMENTAL DETAILS Indium(III) chloride, Na2S×9H2O, 50 w.% aqueous solution of polyethyleneimine (molecular mass M = 50 KDa), polyvinyl alcohol (M = 100 KDa), polyvinylpyrrolidone (M = 360 KDa), gelatin from porcine skin, polyethylene glycol (M = 6 KDa), sodium polystyrenesulfonate, sodium polyphosphate, sodium mercaptoacetate, NaBH4 and NaOH were supplied by Sigma Aldrich. Colloidal In2S3 NCs were synthesized at room temperature via interaction between
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