Synthesis and characterization of L-cysteine capped Mn-doped ZnS quantum dots

Colloidal nanocrystals, also known as quantum dots (QDs), are nanometer-scale semiconductor crystals, defined as particles with physical dimensions smaller than the exciton Bohr radius. These monodispersed nanoparticles are made of a core of semiconductor material (elements from the IIB-VIB, IIIB-VB or IVB-VIB) surrounded by an organic capping layer or passivating molecule, in a diameter typically in the range from 1 to 10 nm [1]. Amidst II–VI semiconductors, zinc sulphide has immense consideration due to its specific band structure, wide band-gap energy and large exciton binding energy [2]. In the present study, Mn-doped ZnS QDs surface-capped with l-cysteine (L-cys) are synthesized. The ZnS quantum dots were further characterized using FESEM, XRD, UV–Visible spectroscopy and FT-IR. The morphology of the prepared L-cys -Mn-ZnS QDs was studied by FESEM . As seen, the QDs possess a spherical morphology with an average particle size of about 7 nm. Typically, the prepared L-cys -Mn-ZnS QDs exhibited a cubic blend structure as revealed by the distinguishable (111), (220), and (311) planes in XRD patterns and the average particle size of QDs was found to be around 6-8 nm by Scherrer s equation [3]. The FT-IR spectra of the L-cys-Mn-ZnS QDs and the free L-cys was investigated and 619 cm−1 (Zn-S vibration) revealed the existence of L-cys -Mn-ZnS QDs [4].