The quantum confinement effect and photoenhancement of photoluminescence (PL) of lead sulphide (PbS) quantum dots (QDs) and lead sulphide/manganese sulphide (PbS/MnS) core shell QDs capped with thiol ligands in aqueous solution were investigated. From PL results, the presence of MnS shells gives a strong confinement effect which translates to higher emission energy in PbS/MnS core shell QDs. Increasing MnS shell thickness from 0.3 to 1.5 monolayers (ML) causes a blueshift of PL peak energies as the charge carriers concentrated in the PbS core region. Enhancement of the PL intensity of colloidal PbS and PbS/MnS core shell QDs has been observed when the samples are illuminated above the band gap energy, under continuous irradiation for 40 min. Luminescence from PbS QDs and PbS/MnS core shell QDs can be strongly influenced by the interaction of water molecules and oxygen present in aqueous solution adsorbed on the QD surface. However, PbS/MnS core shell QDs with a shell thickness of 1.5 ML did not show a PL peak energy stability as it was redshifted after 25 min, probably due to wider size distribution of the QDs.

Systematic study of the effect of chemical vapor deposition conditions on the incorporation of Nb interstitials between NbS₂ layers.

The development of efficient and flexible piezoelectric nanogenerators (PENG) is critical for next-generation energy-harvesting devices. This study reports the direct growth of MoS₂ flakes on flexible carbon cloth (CC) using a water-based Na₂MoO₄ precursor via chemical vapor deposition. The growth of MoS₂ flakes on CC was confirmed by Raman spectroscopy measurements. The frequency difference between the A_1g and E¹_2g modes ranged from 19.9 to 25.1 cm⁻¹, which indicates variation in MoS₂ thickness from a monolayer to a few layers. Photoluminescence (PL) emission from monolayer MoS₂ flakes was observed with a PL peak energy of ~ 1.88 eV. The full width at half maximum of the PL peak was 60 meV, narrower than obtained for MoS₂ on the SiO₂/Si reference. It was found that micro-gaps on the surface of carbon threads may act as nucleation sites for MoS₂ growth, leading to the formation of MoS₂ flakes that protrude from the micro-gaps. In addition, droplets with diameters ranging from 40 to 120 nm were observed. These may be attributed to the formation of Na₂MoO₄ nano-droplets due to the hydrophobic properties of the CC, which then underwent a sulfurization process. Finally, a proof-of-concept PENG was fabricated using the MoS₂/CC and copper electrodes. The device showed a high peak-to-peak voltage of 24 V. This work highlights the potential of water-based precursors for the scalable growth of high-quality MoS₂ on flexible substrates for high-performance energy harvesting and wearable electronics.