Novel and stable Mn2+@Bi2S3quantum dots–glass system with giant magneto optical Faraday rotations

Abstract

Novel, highly stable Bi₂S₃ and Bi_2−xMn_xS₃ quantum dots (QDs)–glass optical nanosystems were architectured successfully. These advanced nanosystems were characterized by High Resolution Transmission Electron Microscopy (HRTEM), UV-Vis-NIR spectroscopy and room temperature photoluminescence (PL) measurements. HRTEM of the Bi₂S₃ QD–glass nanosystem revealed the size of Bi₂S₃ QDs to be in the range of 5–7 nm. However, for the Bi_2−xMn_xS₃ quantum dots (QDs)–glass nanosystem, the size of Bi_2−xMn_xS₃ QDs were around 3–5 nm. The Bi₂S₃ quantum dots exhibit an orthorhombic structure with good crystallinity. Bi_2−xMn_xS₃ QDs also exhibit the same structure with lower ‘d’ values due to Mn²⁺ incorporation. The optical study clearly reveals the growth of Bi₂S₃ and Bi_2−xMn_xS₃ QDs in the glass matrix. Interestingly, a blue shift of the transmission edge was observed by incorporation of Mn²⁺ under the same thermodynamic conditions. Photoluminescence spectra show distinct Bi₂S₃ and Mn²⁺ related emissions, which are excited via the Bi₂S₃ host lattice. The Mn²⁺ emission intensity at 580 nm wavelength confirms the existence of Mn²⁺ in the Bi₂S₃ lattice in the glass matrix. The magneto optical Faraday rotation measurements were performed at room temperature with magnetic fields up to 5.6 mT for all the samples. Significantly, we observed a giant heightening in the Verdet constant i.e. from 159.34 to 507.30 deg T⁻¹ cm⁻¹ after incorporation of Mn²⁺ (0 to 0.4 moles), which is much higher than conventional single crystal systems like TGG, BFG (76.82 deg T⁻¹ cm⁻¹) as well as other materials reported so far. Our strategy provides a versatile route to controlled magneto optical properties of anisotropic semiconductor nanomaterials, which may create new opportunities for photonic devices, magnetic and current sensor applications.