Effect of Metal Ions on Photoluminescence, Charge Transport, Magnetic and Catalytic Properties of All-Inorganic Colloidal Nanocrystals and Nanocrystal Solids

Abstract

Colloidal semiconductor nanocrystals (NCs) provide convenient "building blocks" for solution-processed solar cells, light-emitting devices, photocatalytic systems, etc. The use of inorganic ligands for colloidal NCs dramatically improved inter-NC charge transport, enabling fast progress in NC-based devices. Typical inorganic ligands (e.g., Sn(2)S(6)(4-), S(2-)) are represented by negatively charged ions that bind covalently to electrophilic metal surface sites. The binding of inorganic charged species to the NC surface provides electrostatic stabilization of NC colloids in polar solvents without introducing insulating barriers between NCs. In this work we show that cationic species needed for electrostatic balance of NC surface charges can also be employed for engineering almost every property of all-inorganic NCs and NC solids, including photoluminescence efficiency, electron mobility, doping, magnetic susceptibility, and electrocatalytic performance. We used a suite of experimental techniques to elucidate the impact of various metal ions on the characteristics of all-inorganic NCs and developed strategies for engineering and optimizing NC-based materials.

Infrared Emitting HgTe Quantum Dots and Their Waveguide and Optoelectronic Devices

“…The ALD approach is also related to the replacement of conventional synthesis ligands used to solvate the particles in the particular choice of growth solvent (e. g. short chain mercapto-acids, water soluble thiols, or alkyl-thiols, alkyl-amines, etc) with compact inorganic ligands such as [80] or molecular metal ions [81][82][83] such as metal chalcogenides (zintyls) [84]. Adjacent QDs in films with compact anionic ligands such as S 2− etc, have also been bridged with divalent metal cations to improve and manipulate charge carrier characteristics [85]. These approaches may be used to control the surface stoichiometry (in favourable cases the carrier type may be switched from n-to p-type for example [78,85]) and to reduce the interdot spacing in films of QDs with such capping ligands in order to improve carrier mobilities.…”

Excited-State Dynamics in Colloidal Semiconductor Nanocrystals

“…They provide ''trap states'' for charge carriers, i.e., energy levels within the bandgap where the charge carrier is spatially localized. Indeed, the quantum efficiency of NC emission improves when the NC surface is covered with a protective shell of high-bandgap material [13,15,16,61,74,[243][244][245][246], or when ligands saturate chemical bonds on the surface [16,123,[247][248][249][250][251].…”

“…The simplest picture is that quenching can be suppressed by saturating chemical bonds of the surface atoms [15,16,61,[243][244][245][246][247][248][249]251]. This can be achieved by overcoating the NC either by a shell of another semiconductor or by a ligand layer.…”

Impact of electric field on Hofmeister effects in aggregation of negatively charged colloidal minerals

“…19,20,53 This implies that properties of colloidal surface and cations are equally important in the aggregation of colloidal minerals. Furthermore, similar Hofmeister effects in charged particle interactions were also found by Liu et al 34 and Tian et al 33 In their work, ionic polarization in strong electric field was regarded as the origin of Hofmeister effects in ion-surface interactions.…”

“…12 These effects can influence the interactions of ions with different interfaces (metal/water, air/water, oil/water and water/solid), 13,14 as well as affect the physicochemical properties of the solution or colloids, such as activity coefficient, Zeta potential, freezing point, osmotic pressure, photoluminescence and catalytic properties. [14][15][16][17][18][19][20] The widespread applicability of Hofmeister effects in different fields and their unclear origin make the clarification of the underlying mechanism one of the tremendous challenges in interfacial and colloidal science. Many efforts have been made to uncover the origin of Hofmeister effects.…”