Colloidal synthesis and optical properties of ultra-small CdTe quantum dots

K.S. Dremliuzhenko; B.N. Kulchytskyi; D.V. Korbutyak; O.G. Kosinov; O.F. Isaieva; N.V. Mazur; L.I. Trishchuk

doi:10.15330/pcss.25.4.838-843

Authors

K.S. Dremliuzhenko V.E. Lashkarev Institute of Semiconductor Physics NAS of Ukraine, Kyiv, Ukraine
B.N. Kulchytskyi V.E. Lashkarev Institute of Semiconductor Physics NAS of Ukraine, Kyiv, Ukraine
D.V. Korbutyak V.E. Lashkarev Institute of Semiconductor Physics NAS of Ukraine, Kyiv, Ukraine
O.G. Kosinov V.E. Lashkarev Institute of Semiconductor Physics NAS of Ukraine, Kyiv, Ukraine
O.F. Isaieva V.E. Lashkarev Institute of Semiconductor Physics NAS of Ukraine, Kyiv, Ukraine
N.V. Mazur V.E. Lashkarev Institute of Semiconductor Physics NAS of Ukraine, Kyiv, Ukraine
L.I. Trishchuk V.E. Lashkarev Institute of Semiconductor Physics NAS of Ukraine, Kyiv, Ukraine

DOI:

https://doi.org/10.15330/pcss.25.4.838-843

Keywords:

synthesis technology, ultrasmall quantum dots, centrifugation, absorption spectra, photoluminescence, photoluminescence excitation spectra

Abstract

The colloidal synthesis of CdTe nanocrystals (NCs) in a reactor whose reaction medium consists of a solution of CdI₂ salt, thioglycolic acid (TGA), and NaOH alkali. The gaseous precursor H₂Te, which was obtained electrochemically in a galvanostatic cell, was passed through this solution. The size of the synthesized NCs was varied by egulating the flow of hydrogen telluride from galvanostatic cell. In turn, the outflow of hydrogen telluride depends on the current that passes through the cell electrodes. The growth rate of nanocrystals is determined by the rate of precursor feeding into the reactor. Studies have shown that this synthesis usually produces CdTe NCs of different sizes. To separate the colloidal solution into fractions, a centrifugation method was proposed, which allowed to isolate ultra-small quantum dots (USQDs) of CdTe with dimensions of about 2 nm. To obtain QDs of ultra-small size, we used low current values (up to 100 mA), a short synthesis time (0.5-1 min), and high pH values (8-11) of the reaction medium. The study of the absorption spectra of CdTe NC samples taken from the fraction with the smallest size separated by centrifugation showed that the energy of the corresponding transitions significantly exceeds the band gap of bulk CdTe (1.5 eV), and which correspond to CdTe USQDs (clusters). Our study of the size of CdTe on the Zetasizer Nano ZS confirmed the presence of USQDs with dimensions of approximately 2 nm. It has been shown that the photoluminescence of the USQDs is mainly due to surface defects.

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