Investigações de propriedades estruturais, eletrônicas, ópticas e magnéticas de nanocristais Bi2-xFexS3, Bi2-xCoxS3, Bi2-xCrxS3 e Sb2-xMnxS3 em matrizes vítreas

Abstract

Nanocrystals (NCs) Bi2-xFexS3, Bi2-xCoxS3, Bi2-xCrxS3 and Sb2-xMnxS3 Dilute Magnetic Semiconductors (DMS) belong to a new class of materials, with technological potential for application in optoelectronic and spintronic devices. The structural, electronic, optical and magnetic properties of these DMS NCs account for the quantum confinement regime and the sp-d exchange interaction between the charge carriers of the host semiconductors and the unpaired electrons of the transition metal (TM). In this thesis, for the first time, the effects of quantum confinement and variable x-concentration of Fe, Co, Cr and Mn ions on Bi2S3 and Sb2S3 NCs sites embedded in glass were investigated. Transmission electron microscopy images showed the NCs diameter and dhkl crystalline planes, corresponding to the X-ray diffraction patterns of Bi2S3 and Sb2S3 semiconductors. Qualitative analysis performed by energy dispersive X-ray spectroscopy suggested the chemical elements present in the samples. For Bi2-xFexS3 NCs, the spin magnetic moment and fine resonant transitions and calculations of band structures, unit cell volume and Bader charges confirmed the Fe3+ ions in the Bi2S3 crystal structure. For Bi2-xCoxS3 NCs, optical absorptions in the visible and infrared region and the eight spin hyperfine resonant lines confirmed the Co2+ ions in tetrahedral sites in crystalline Bi2S3. For Bi2-xCrxS3 NCs, Raman vibrational modes, optical absorptions in the visible region and calculations of band structures, unit cell volume and spin magnetic moment verified the Cr3+ ions in the octahedral sites in Bi2S3 crystal. For Sb2-xMnxS3 NCs, the six spin hyperfine resonant lines and Raman vibrational modes confirmed the presence of Mn2+ ions in Sb2S3 crystalline sites. SMD NCs formed and grown in glass matrices by fusion and heat treatment methods, have intrinsic and adjustable properties depending on the size and TM doping ions concentration, for technological applications and future research in nanotechnology.