Room Temperature Colloidal Coating of II–VI Nanoplatelets with Quantum Dots

Abstract

The low-temperature colloidal production of II−VI nanoplatelet heterostructures has stimulated the interest of researchers due to the possible uses of these materials in various optoelectronic devices. Here, we report a roomtemperature coating by CdS or ZnS dots of preprepared CdSe nanoplatelets. The dot coating process made use of a synthesis developed for the formation of freestanding CdS and ZnS species, involving injection of a metal precursor into reactive sulfur−amine solutions at room temperature. CdSe structured nanoplatelets with 1.75 nm thickness were used as the core constituent. The structural properties were investigated using Fourier transform infrared spectroscopy and advanced electron microscopy, while the elemental mapping was verified using high-angle annular dark field transmission electron microscopy. The results showed a dots-on-plate structure, resembling an intermediate configuration between core/crown or core/shell heterostructures. A thorough study of optical properties demonstrated a dramatic spectral shift of the absorption edge to lower energies, regardless of the uniformity of the coating layer, maintaining spectral stability over two months while stored at ambient conditions. Other optical measurements included examination of temperature-dependent photoluminescence and transient photoluminescence decay, from room temperature down to ∼4 K. These measurements revealed excitons, trions, and trapped carrier recombination emission with variable relative intensities following the temperature change. The dots-on-plate structures studied displayed a short photoluminescence decay (≤nanosecond), compatible with that of core/shell (crown) structures prepared at high temperatures. As a result, the presented techniques are alternative pathways that eliminate the requirement for excessive temperatures and/or multistep processes, instead providing rapid, inexpensive, and scalable procedures with practical advantages.

The Tuning of Exciton‐Phonon Coupling in Colloidal Nanocrystals by a Dielectric Medium

“…The PL curve is related to the hh‐e recombination emission, with an FWHM of 55 meV and quantum efficiency of 37%. [ 7 ]…”

“…The low‐temperature transient PL measurements of core (Figure S7A, Supporting Information) and core/shell (Figure S7B, Supporting Information) NPLs revealed respective decay times of 280 and 374 ps for the neutral exciton, and 570 ps and 1.22 ns for the trion recombination, values that are in agreement with a previous publication, and further confirm the assignment of the exciton bands. [ 7 ]…”

“…This procedure was adopted from a previously published work. [ 7 ] A mixture of 1 mL of preprepared CdSe NPLs, 4 mL of chloroform, 0.1 g of TAA, 1 mL of octylamine was sonicated for 10 mins until the mixture was fully dissolved. Afterward, 350 µL of 0.2 m Cd(NO 3 ) 2 ·4H 2 O in ethanol was added.…”

“…Colloidal semiconductor nanocrystals (NCs) have attracted scientific and technological interest during the past thirty years due to their tunable optical properties with variations in size, shape, and composition. [1][2][3][4] Numerous studies have been conducted to explore their optical and electrical properties, including the analysis of fluorescence quantum yields, [5][6][7] electron-hole exchange interactions, [8] excited-state lifetime, [9][10][11][12] QDs. Mack et al [38] showed broadening of surface exciton emission due to resonance coupling to ligand vibrational modes.…”

High-Sensitivity Organic–Inorganic Hybrid Materials with Reversible Thermochromic Property and Dielectric Switching

“…Besides, for most inorganic discoloration materials, for instance, VO 2 (M)@SiO 2 , a higher temperature is required during synthesis. In contrast, inorganic–organic hybrids, − as a composite material, show potential intriguing properties arising from their interactions (inorganic and organic materials). − Particularly, with the special structural flexibility and energy band property, metal halide hybrid materials have undergone a rapid development. − …”