Optical, structural and magnetic characterization of Bi2-xCrxTe3 nanocrystals in oxide glass

Chromium-doped bismuth telluride (Bi2-xCrxTe3) diluted magnetic semiconductor nanocrystals were successfully synthesized in a glass matrix by the fusion method with nominal Cr concentrations of x = 0.00, 0.05, and 0.10. Transmission electron microscopy confirmed the growth of nanocrystals with an average diameter of similar to 5.0nm. Shifts in X-ray diffraction peaks with increasing x indicated substitutional inclusion of Cr ions (occupying Bi sites - Cr-Bi) in the Bi2Te3 structure. The absorption spectra for x = 0.05 and 0.10 show two intense spin-allowed bands at similar to 425 and 635 nm and two minor spin-forbidden bands at similar to 650 and 685 nm. These bands were attributed to the Cr3+ d-d transitions, according to the crystal field theory. Finally, electron paramagnetic resonance spectra from the Bi2-xCrxTe3 nanocrystals displayed Cr3+ characteristics with spin 3/2 in the d(3) state, thereby confirming the trivalent state of Cr ions in the Bi2Te3 structure.