Concentration effect on the optical and magnetic properties of Co2+-doped Bi2S3 semimagnetic nanocrystals growth in glass matrix

Abstract We investigate the effect of cobalt (Co) concentration on the optical, structural and magnetic properties of Bi 2-x Co x S 3 nanocrystals grown in a glass matrix produced by the fusion method. Transmission electron microscopy images showed the nanocrystals formed within the glass matrix with average sizes between 3.5 and 6.5 nm, and interplanar distances d 212  = 0.280 nm and d 210  = 0.320 nm which corresponds to the Bi 2 S 3 semiconductor. The diffraction patterns show the peaks associated with the (210) and (212) planes. The analyzes by energy dispersion spectroscopy in the samples confirmed the presence of the chemical elements of S, Bi and Co. The optical absorption spectra and crystal field theory indicates that Co 2+ ions is incorporated in the tetrahedral site into Bi 2 S 3 nanocrystals, displaying characteristic transitions in the electromagnetic spectral range visible 4 A 2 ( 4 F) →  4 T 1 ( 4 P) and near-IR 4 A 2 ( 4 F) →  4 T 1 ( 4 F). The crystal field strength Δ = 3891 cm −1 and the Racah parameter B = 791 cm −1 are estimated for the tetrahedral coordinated Co 2+ ions into Bi 2 S 3 nanocrystals. The sp-d exchange interactions are overlap due to the quantum confinement effect located in the band-gap of the semiconductor. Electron spin resonance shows the result of the eight hyperfine lines characteristic of the electronic states Ms  = 1/2 ↔ −1/2 when they are placed in a tetrahedral crystalline field due to the interaction between the electron spin (S = 3/2) and the nuclear spin (I = 7/2) of Co 2+ ions (3d 7 ).