Noticeable size dispersity and optical stability of sodium dodecyl sulphate (SDS)-coated MnSe quantum dots in extreme natural environment

Abstract

The pH of the dispersing media has an influential role on the optical and radiative features of quantum particles/dots (QDs). Herein, we report size dispersity and luminescence response of sodium dodecyl sulphate (SDS)-coated MnSe QDs dispersed in extreme natural extracts. The hydrothermally processed QDs exhibited wutzite phase and numerous Raman active modes as revealed through the X-ray diffraction and Raman spectroscopy studies; respectively. Of varied pH (typically, from 2.5 to 9), distinctly different extracts were derived from starfruit, sugarcane, chilli, and neem leaves available locally. The hydrodynamic size of the QDs experiences a declining trend with increasing pH, with dispersing media being a buffer solution or a natural extract. Zeta potential makes a clear transition from the positive to the negative values, as one moves from a low (acidic) to high (basic) pH of the natural extracts, and subsequently, the isoelectric point (IEP) of the QDs in a medium has been predicted at pH 6.3. Whereas a more acidic medium offered a relatively lowered luminescence profile, the extracts of high pH ensured an intense blue–violet emission of the QDs located at ~ 428 nm along with defect-mediated peaks, expected at relatively higher wavelengths. Furthermore, the acidic environment tends to suppress both near band edge and defect-mediated emissions substantially. The optical stability of surfactant-coated QDs would find immense value in the areas of nano-bio interface applications, such as nano-bioconjugation, bio-imaging, and drug formulation in nano-medicine.