PbS quantum dots (PbS-QDs) are one of the best candidates in new generation of LEDs. When the PbS-QDs are exposed to light spectrum, the electrons in the valence band (VB) are excited to the conduction band (CB). The excited electrons then return from the CB to the VB and release extra energy by emitting light. The return of electrons to the VB makes it possible to repeat the light absorption-emission circle. If the size of the PbS-QDs is smaller than the Bohr magneton radius (PMR), the probability of the electron return to the VB decreases. This leads to phenomena named quantum dot blinking (QDB) in light-emitting diodes (LEDs), which is not desirable. In this research, a new approach has been proposed in which the addition of a metal substrate for PbS-QDs with a semiconductor shell with a suitable band edge could increase PbS-QDs efficiency in QD-LEDs and overcome the QDB problem.

In this study, lead sulfide (PbS) films were grown on Fluorine-doped Tin Oxide (FTO) glass substrate by thermal evaporation in a horizontal furnace to investigate carrier gas effect on structural, morphological, elemental, optical, electrical and photovoltaic properties of PbS. X-ray diffraction (XRD) patterns confirmed the formation of cubic polycrystalline PbS particles for all samples. The results showed that using Ar+H2 as a carrier gas increased crystallite size of the film. Field emission scanning electron microscopy (FESEM) images showed nano-dimension surface morphologies and revealed that using carrier gas can make the obtained films and their surface porosities more uniform and regular. Also, the elemental analysis demonstrates that using mixed carrier gas provides a better stoichiometry for PbS film. Optical and electrical evaluations indicated improvements in absorption intensity and electrical conductivity of the PbS film when using the mixed carrier gas. Finally, the deposited films were characterized as solar cells and their quality parameters (QP) were extracted and presented. The obtained results illustrate the improvement in QPs of PbS solar cell when using mixed carrier gas.

Magnesium ferrite (MgFe2 O4 ) as a core magnetic nanostructure was synthesized via auto combustion method by using grapefruit extract as a biocompatible and cost-effective material. Then flower and star-like PbS were synthesized using thioglycolic acid as a sulfur source without using any chemical template. After that for preparation of magnetic and photocatalyst MgFe2 O4-PbS nanocomposites, lead sulfide were coated on the magnetic core by hydrothermal procedure. Morphology of the prepared products was estimated by transmission electron microscopy (TEM), scanning electron microscopy (SEM), also X-ray diffraction (XRD) pattern show purity and phase of the product. Fourier transforms infrared (FT-IR) spectroscopy show vibration modes of the bonds. Vibrating sample magnetometer (VSM) illustrated that magnesium ferrite nanoparticles have a soft magnetic behaviour with 18 emu/g magnetization and coercivity about 90Oe. The photocatalytic behaviour of MgFe2 O4-PbS nanocomposites were examined using the degradation of two various azo dyes acid brown and acid violet under visible light irradiation. This magnetic photocatalyst can easily separate from water with an external magnetic field and can be used under solar irradiation.