Tuning Optical Activity of IV–VI Colloidal Quantum Dots in the Short-Wave Infrared (SWIR) Spectral Regime

Abstract

The achievement of tunable optical properties across a wide spectral range, along with an efficient surface passivation of lead chalcogenide (PbSe) colloidal quantum dots (CQDs), has significant importance for scientific research and for technological applications. This paper describes two comprehensive pathways to tune optical activities of PbSe CQDs in the near-infrared (NIR, 0.75−1.4 μm) and the short-wave infrared (SWIR, 1.4−3 μm) ranges. A one-pot procedure enabled the growth of relatively large PbSe CQDs (with average sizes up to 14 nm) exploiting programmable temperature control during the growth process. These CQDs showed optical activity up to 3.2 μm. In addition, PbSe/PbS core/shell CQDs prepared by an orderly injection rate led to an energy red-shift of the absorption edge with the increase of the shell thickness, whereas a postannealing treatment further extended the band-edge energy toward the SWIR regime. A better chemical stability of the CQDs with respect to that of PbSe core CQDs was attained by shelling of PbSe by epitaxial layers of PbS, but limited to a short duration (<1 day). However, air stability of the relatively large PbSe as well as the PbSe/PbS CQDs over a prolonged period of time (weeks) was achieved after a postsynthesis chlorination treatment.

High‐Performance n‐ and p‐Type Field‐Effect Transistors Based on Hybridly Surface‐Passivated Colloidal PbS Nanosheets

“…To overcome this problem, the idea of hybrid passivation of these crystals has been suggested by employing X‐type elemental inorganic ligands in addition to their organic ligands. It has been shown for 0D nanoparticles that halide ions, as atomic point‐like ligands, can penetrate into the organic layer and passivate the remaining dangling bonds between them . In order to passivate the surface, halide ions can be introduced to the crystal either after the synthesis .…”

“…In order to passivate the surface, halide ions can be introduced to the crystal either after the synthesis . or during the synthesis as the precursor or as the coligands . In our case, halogenoalkanes which are used as coligands decompose during the synthesis and produce halide ions.…”

“…The colloidal synthesis of nanomaterials offers the possibility to produce high‐quality and inexpensive crystals which are confined in one to three dimensions . Recently, we showed that this method can also be used for the synthesis of 2D materials such as lead sulfide nanosheets .…”

Halogens in the Synthesis of Colloidal Semiconductor Nanocrystals

“…The absorption spectra of these particles remained unchanged after some weeks of air exposure, while without the treatment they experienced a fast degradation ( Fig. 5 B) [39,41]. Further, their functionality as field-effect transistors (FETs) has been preserved even in air, demonstrated by a pronounced n-type behavior [39].…”

“…For instance, an ammonium chloride solution (or other ammonium halides [39]) was added to the reaction mixture after cooling the solution down. This method has been used for passivation of PbS NCs [39] or PbSe NCs (with or without a PbS shell) [41] and has led to air stability of the particles for weeks. The absorption spectra of these particles remained unchanged after some weeks of air exposure, while without the treatment they experienced a fast degradation ( Fig.…”