Investigation of structural and optical properties of Pb1-xCoxS nanocrystals embedded in chalcogenide glass

Abstract

Diluted magnetic semiconductor Pb1-xCoxS nanocrystals with nominal concentrations of Co (x = 0.00, 0.10 and 0.16) embedded in a chalcogenide glass matrix were synthesized by the low-cost fusion-nucleation method that allows for the manipulation, control, and tuning of the structural, optical, and electronic properties. Transmission electron microscopy images showed the formation and growth of the Pb1-xCoxS nanocrystals to be dependent on the thermal annealing time at 500 °C. Energy dispersive X-ray spectroscopy analysis confirmed the chemical elements Pb, S and Co in the nanocrystal. X-ray diffraction measurements showed characteristic peak patterns of the PbS rock-salt crystal structure with displacement to greater angles of the plane (111) with the xCo doping. Magnetic force microscopy measurements showed the magnetic phase-contrast patterns, providing additional evidence of incorporation of Co into the PbS structure. The energy parameters of the crystal field strength (Δ = 3898 cm−1), Racah (B = 794 cm−1) and spin-orbit coupling (λ = - 555 cm−1) that are part of the sp-d exchange interactions of Co2+ ions in tetrahedral sites [CoS4]6- in Pb1-xCoxS nanocrystals were determined by UV-VIS-NIR optical absorption spectra and the crystalline field theory from the Tanabe-Sugano diagram for d7 ion in a ligand tetrahedral.