PbS Quantum Dots with Stable Efficient Luminescence in the Near‐IR Spectral Range

Abstract

Rapid progress in tailoring the size and shape of semiconductor nanocrystals (quantum dots) enables a high degree of control over their optical and electronic properties. This control can be harnessed for applications in biological assays, optoelectronic integration, and wireless-systems engineering. In optoelectronics, size tunability of quantum dots permits control over the spectrum of absorption for photovoltaic and photoluminescent, stimulated emission, and electroluminescence applications, [1±4] whereas in biological applications, this allows spectral multiplexing and coding. [5] In both applications, luminescence in the near-infrared region is urgently needed: in optoelectronics to bridge interconnects with shortand medium-haul networks, and in biological applications to exploit the spectral windows in water and biological absorption. An ideal nanocrystal (NC) synthetic route combines features that have so far been demonstrated in isolation. Synthesis in aqueous solution, or transfer from organic media to water, is highly desirable for compatibility with biological assays.[5] It also enables multilayer polymer±nanocrystal device fabrication for heterostructure engineering through the use of alternating aqueous/organic solvents in sequential layers.Other crucial features of synthetic route are simplicity, use of non-toxic solvents, and moderate reaction temperatures. [6,7] From the point of view of the resulting material properties, the NCs desired in the above-mentioned applications would be size-tunable in the near-IR spectral range; have a high quantum yield, and exhibit stable, narrow fluorescence peaks [8] requiring no yield-reducing size-selective precipitation.To date, no route to synthesis of quantum dots (QDs) has been reported that accommodates all of these features simultaneously. We report herein a one-stage water-based synthesis of stable and monodisperse PbS NCs that show photo-and electroluminescence in the spectral range 1000±1400 nm. It is the combination of the simplicity of water-based synthesis, a one-stage process with no need in encapsulation or size-selective precipitation, relatively low toxicity, [9,10] stability, size tunability, and excellent performance that make these NCs promising in optoelectronic and biological applications. PbS nanocrystals were prepared in aqueous solutions using a mixture of thiols as a stabilizing agent. We admit that waterbased synthesis and thiol ligands have been used in II±VI nanoparticle synthesis. [11,12] This approach, however, has not been tested in the preparation of PbS NCs: previous reports on PbS nanoparticles synthesis in aqueous solutions employed poly(vinyl alcohol), poly(vinyl pyrrolidone), gelatin, and DNA as stabilizers. [13,14] These reports and our experiments indicate that these methods result in agglomerates of poly/ nanocrystals of very small diameter (~1 nm) and absorption and luminescence in the visible spectral range. We examined a number of different capping agents, such as thiobutanol, thiohexanol, triglycolic acid, thioglycero...

Deep-tissue anatomical imaging of mice using carbon nanotube fluorophores in the second near-infrared window

“…QDs (11) such as PbSe (12), PbS (13), and CdHgTe (14) are promising candidates for imaging in the NIR II; however, in vivo animal imaging in the NIR II region with QDs has not been carried out thus far. As an alternative, singlewalled carbon nanotubes (SWNTs) have shown promise as fluorescent imaging agents in the NIR II both in vitro and in vivo (15)(16)(17)(18).…”

Near-infrared electroluminescent devices based on colloidal HgTe quantum dot arrays

“…[2][3][4][5][6][7] In recent years, in order to explore their potential for use at telecommunications wavelengths, efforts have been made to extend the optical response of colloidal quantum dots from the visible to the near-infrared ͑NIR͒ by the synthesis of nanocrystals based on, e.g., InAs, PbS, PbSe, and HgTe. [8][9][10][11][12] As a result, an initial demonstration of phenomena, such as size-tunable NIR luminescence, electroluminescence ͑EL͒ and optical gain, has been possible. [13][14][15][16][17] Concerning HgTe, in particular, this material has an inverted band structure and an essentially negative band gap of around Ϫ0.15 eV at 295 K. 18 It is expected that the effect of quantum confinement in HgTe quantum dots should increase the effective band gap of the material and give rise to NIR luminescence.…”

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

“…[ 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%.…”