Preparation of fluorescent CdTe@CdS core@shell quantum dots using chemical free gamma irradiation method

This study investigates pH dependent gamma radiation effects on Mercaptopropionic Acid (MPA) capped CdTe quantum dots (QDs). Gamma radiation, as fast and chemical free catalyser, causes CdS Shell formation on MPA capped CdTe QDs at very high alkaline environment. UV–vis absorption spectroscopic results showed that, with increase in gamma radiation doses, the absorption peak of CdTe QDs decreased to lower wavelength (decrease in particle size) in both acidic & neutral medium (as synthesised), and it increased towards longer wavelength in basic medium indicating the possibility of growth of CdS shell over CdTe core QDs. X-ray diffractogram studies have revealed that the peaks of CdTe QDs shift towards higher angles after irradiation, supporting the notion of the core@shell particle structure of CdTe@CdS. TEM images confirmed the extra stretch around core particles from CdS material resulted in increase of average size of QDs. EDX study revealed the chemical composition of material system. X-ray photoelectron spectroscopic results revealed the shift in the binding energy of both Cd and S thereby indicating the change in the coordination condition after irradiation promoted the particles' formation of core@shell in nature. The systematic photoluminescence spectroscopic investigation at all possible pH values against ascended gamma radiation doses revealed the formation of CdS shell over CdTe core at optimum pH value (i.e. only at basic pH 12). Contrarily, photo-oxidation of QDs' was observed at neutral (and below) pH values towards gamma irradiation. The quantum yield is increased only after introducing external shell source material at highest alkaline media confirming the formation of CdS shell on CdTe core.