Paramagnetic, Near‐Infrared Fluorescent Mn‐Doped PbS Colloidal Nanocrystals

Abstract

The nanoscale design of nanocrystals by the controlled incorporation of dopant impurities is a research fi eld of fundamental interest with great potential for numerous disruptive technologies. [1][2][3] In particular, 3 d transition metal ions (Mn, Co, etc.) with their d -shell electronic confi gurations can imprint a nanocrystal with magnetic properties of relevance for innovative applications ranging from bio-imaging [ 4,5 ] to spintronics. [ 1,5 ] For example, colloidal nanocrystals doped with transition metals could provide versatile contrast agents for multimodal medical imaging, i.e., for contrast-enhanced magnetic resonance imaging (MRI) and confocal microscopy. [ 4 ] To date, a variety of nanoparticles (e.g., Fe 3 O 4 , FePt, MnFe 2 O 4 , and MnO) have been used for enhancedcontrast MRI, [ 5,6 ] but these require functionalization with fl uorescent organic dyes for optical imaging and their solubility in physiological solvents demands modifi cation of the nanocrystal surface. Luminescent, paramagnetic colloidal quantum dots, QDs (e.g., Mn-doped Si, ZnS, CdS/ZnS QDs) have also been previously studied. [7][8][9] However, these nanostructures require phase transfer to address water solubility and/or the visible photoluminescence (PL) emission limits their application in in vivo imaging due to strong photon absorption by biological tissues. Thus despite extensive research in this fi eld, paramagnetic nanoparticles with fl uorescence in the near-infrared (NIR) spectral region of the biological optical window are still not available.In this work, we report paramagnetic, NIR fl uorescent Mndoped PbS colloidal nanocrystals in an aqueous solution. We demonstrate the successful incorporation of Mn atoms in the nanocrystals, which contain up to 8% Mn. The nanocrystals are optically active at room temperature in the technologically important biological window between 1.2 μ m and 0.8 μ m; also, the Mn atoms imprint the nanoparticles with paramagnetic properties. Preliminary cytoxicity studies show that the exposure of human cell lines to the nanoparticles at concentrations up to 0.2 mg mL −1 does not induce any adverse effect, thus providing guidelines on safe doses for further toxicology studies and future applications in medical imaging.Our Mn-doped PbS nanocrystals in an aqueous solution differ from previously reported nanostructures based on PbS nanowires [ 10,11 ] and PbS nanocrystals in glass matrices [ 12,13 ] or in organic solvents. [ 14 ] To synthesize the Mn-doped PbS nanoparticles, we prepared a Pb 2+ precursor solution containing 2.5 × 10 −4 mol of lead acetate Pb(CH 3 COO) 2 , 1.5 × 10 −3 mol of thioglycerol (TGL) and 5 × 10 −4 mol of dithioglycerol (DTG) in 15 mL of deionized water, where the thiols act as capping agents. [ 15,16 ] The pH of the solution was adjusted to a value of 11.0 by addition of triethylamine. While maintaining the pH of the solution, manganese acetate Mn(CH 3 COO) 2 salt was added with Mn concentration, x , up to 18%. To facilitate the incorporation of the Mn atoms during the nu...

Spin manipulation and spin-lattice interaction in magnetic colloidal quantum dots

“…Colloidal Mn-doped PbS QDs with average diameter of 4.5 ± 1.2 nm were synthesized in aqueous solution with Mn weight content, x, from 0.05% to 0.5 %, as detailed in Ref. [14], which corresponds to a statistical number of Mn ions per QD (Mn:QD) from 1:2 to 5:1 (Table I). Our approach enables the incorporation of Mn 2+ ions into QDs and the controlled modification of their optical and magnetic properties.…”

Exploring the effect of manganese in lead sulfide quantum dot sensitized solar cell to enhance the photovoltaic performance

“…[20] In QDSSCs, several approaches are used, such as crystal size control, introducing dopants, and optimizing the QD-sensitized importance in the exploration, the incorporation of Mn into PbS is an important methodology because it imparts paramagnetic properties. [25] Carrier-dopant exchange interactions occur in Mn doped PbS colloidal quantum dots, which leads to enhancements in both the valence and the conduction electrons. [26] Justin et al worked on ZnO nano-rods with CdS/CdSe/ZnS and presented a promising passivation layer for PbS QDs which defends against polysulfide electrolyte and the large accumulation of photo-injected electrons in the conduction band of the photo-anode.…”

Giant photocurrent enhancement by transition metal doping in quantum dot sensitized solar cells

“…The hyperfine constant obtained from the EPR spectrum, is 266 6 1 MHz, which is in agreement with the previously obtained values. [14][15][16] The g factor is close to 2. Moreover, we also observe the forbidden M ¼ 61 transitions, which are seen as the shoulder peaks.…”