Alessandra S. Silva

Evidence of competition in the incorporation of Co2+ and Mn2+ ions into the structure of ZnTe nanocrystals

Glass-embedded Zn1−x−yMnxCoyTe nanocrystals (with x = 0.01 and y varying from 0.000 to 0.800) were successfully synthesized using a protocol based on the melting–nucleation synthesis route and herein investigated by several experimental techniques. Optical absorption (OA) provides evidence of the incorporation of substitutional Co2+ ions in the semiconducting Zn1−x−yMnxCoyTe lattice and shows that with increasing Co concentration these ions may also be dispersed into the glass matrix, causing structural disorder. Atomic force microscopy (AFM) images reveal the size of the nanocrystals and magnetic force microscopy (MFM) gives evidence of the paramagnetic behavior of the doped samples. X-ray diffraction (XRD) and Raman scattering reveal that high Co concentrations increase the structural disorder in the host glass matrix. Electron paramagnetic resonance (EPR) spectroscopy reveals the presence of Mn2+ ions inside and at (or near) the surface of the ZnTe nanocrystals, and also that the increase of Co doping concentration reduces the incorporation of Mn2+ ions into the ZnTe structure, simultaneously increasing their dispersion into the glass matrix.

Optical properties of Cr-doped Zn1−xMnxTe semimagnetic nanocrystals

The effect of Cr co-doping on the optical properties of Mn-doped ZnTe nanocrystals (NCs) embedded in a glass matrix is studied in this paper. The substitutional incorporation of Cr2+ ions into these semiconducting NCs was strongly evidenced by optical absorption and crystal field theory analyses, which showed the characteristic transitions of Cr2+ and Cr3+ ions. Transmission electron microscopy images revealed the NC size and invariance lattice parameter, with the incorporation of Mn2+ and Cr2+ ions. PL spectra showed that co-doping with Cr favors a competition between Mn2+ and Cr2+ ions, resulting in a decrease in the rate of Mn2+ substitution, zinc vacancy filling (VZn) in Zn1−x−yMnxCryTe NCs, and the formation of interstitial Cr3+ ions in the host glass system.