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1. Kinetic analysis of the growth of semiconductor nanocrystals from the peak wavelength of photoluminescence

   https://doi.org/10.1051/epjap/2022210286  

   Yang, Fuqian (January 2022, The European Physical Journal Applied Physics)

   Understanding the rate processes controlling the growth of semiconductor nanocrystals in liquid solutions is of great importance in tailoring the sizes of semiconductor nanocrystals for the applications in optoelectronics, bioimaging and biosensing. In this work, we establish a simple relationship between the photoluminescence (PL) peak wavelength and the growth time of semiconductor nanocrystals under the condition that the contribution of electrostatic interaction to the quantum confinement is negligible. Using this relationship and the data available in the literature for CdSe and CdSe/ZnS nanocrystals, we demonstrate the feasibility of using the PL peak wavelength to analyze the growth behavior of the CdSe and CdSe/ZnS nanocrystals in liquid solutions. The results reveal that the diffusion of monomers in the liquid solution is the dominant rate process for the growth of CdSe/ZnS nanocrystals, and the activation energy for the growth of CdSe nanocrystals in the liquid solution is ∼9 kJ/mol. The feasibility to use this approach in the analysis of the thickness growth of core–shell nanocrystals with and without mechanical stress is also discussed. Such an approach opens a new avenue to in-situ monitor/examine the growth of semiconductor nanocrystals in liquid solutions. 

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2. Size- and temperature-dependent photoluminescence spectra of strongly confined CsPbBr ₃ quantum dots

   https://doi.org/10.1039/d0nr02711a  

   Cheng, Oscar Hsu-Cheng; Qiao, Tian; Sheldon, Matthew; Son, Dong Hee (June 2020, Nanoscale)

   null (Ed.)

   Lead-halide perovskite nanocrystals (NCs) are receiving much attention as a potential high-quality source of photons due to their superior luminescence properties in comparison to other semiconductor NCs. To date, research has focused mostly on NCs with little or no quantum confinement. Here, we measured the size- and temperature-dependent photoluminescence (PL) from strongly confined CsPbBr 3 quantum dots (QDs) with highly uniform size distributions, and examined the factors determining the evolution of the energy and linewidth of the PL with varying temperature and QD size. Compared to the extensively studied II–VI QDs, the spectral position of PL from CsPbBr 3 QDs shows an opposite dependence on temperature, with weaker dependence overall. On the other hand, the PL linewidth is much more sensitive to the temperature and size of the QDs compared to II–VI QDs, indicating much stronger coupling of excitons to the vibrational degrees of freedom both in the lattice and at the surface of the QDs. 

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3. Polysalt ligands achieve higher quantum yield and improved colloidal stability for CsPbBr ₃ quantum dots

   https://doi.org/10.1039/d1nr04753a  

   Wang, Sisi; Du, Liang; Donmez, Selin; Xin, Yan; Mattoussi, Hedi (October 2021, Nanoscale)

   Colloidal lead halide perovskite quantum dots (PQDs) are relatively new semiconductor nanocrystals with great potential for use in optoelectronic applications. They also present a set of new scientifically challenging fundamental problems to investigate and understand. One of them is to address the rather poor colloidal and structural stability of these materials under solution phase processing and/or transfer between solvents. In this contribution, we detail the synthesis of a new family of multi-coordinating, bromide-based polysalt ligands and test their ability to stabilize CsPbBr 3 nanocrystals in polar solutions. The ligands present multiple salt groups involving quaternary cations, namely ammonium and imidazolium as anchors for coordination onto PQD surfaces, along with several alkyl chains with varying chain length to promote solubilization in various conditions. The ligands provide a few key benefits including the ability to repair damaged surface sites, allow rapid ligand exchange and phase transfer, and preserve the crystalline structure and morphology of the nanocrystals. The polysalt-coated PQDs exhibit near unity PLQY and significantly enhanced colloidal stability in ethanol and methanol. 

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4. Eco-friendly synthesis and stability analysis of CsPbBr ₃ and poly(methyl methacrylate)-CsPbBr ₃ films

   https://doi.org/10.1088/1361-6528/adbbf6  

   Huang, You-Lin; Li, Wei; Yang, Fuqian (March 2025, Nanotechnology)

   Abstract This study presents an eco-friendly mechanochemical synthesis of cesium lead bromide (CsPbBr₃), eliminating the need of organic solvents and high temperatures. The synthesized CsPbBr₃powder is used to fabricate poly(methyl methacrylate) (PMMA)-CsPbBr₃films and CsPbBr₃nanocrystals (NCs). The photoluminescence (PL) peaks of the emission light are centered at 541 nm, 538 nm, and 514 nm for the CsPbBr₃powder, PMMA-CsPbBr₃films, and CsPbBr₃NCs, respectively, correlating with crystal sizes of 0.96, 0.56, and 0.12μm, respectively. The PL lifetime analysis reveals decay times ( ${\tau }_1,{\tau }_2$) of (4.18, 20.08), (5.7, 46.99), and (5.81, 23.14) in the units (ns, ns) for the CsPbBr₃powder, PMMA-CsPbBr₃films, and CsPbBr₃NCs, respectively. The PL quantum yield of the CsPbBr₃NCs in toluene is 61.3%. Thermal activation energies for thermal quenching are 217.48 meV (films) and 178.15 meV (powder), indicating improved thermal stability with the PMMA encapsulation. The analysis of the PL intensity decay from water diffusion in the PMMA-CsPbBr₃films yields 1.70 × 10⁻¹²m²s⁻¹for the diffusion coefficient of water, comparable to that for water diffusion in pure PMMA. This work demonstrates a scalable, sustainable strategy for CsPbBr₃synthesis and stability enhancement for optoelectronic applications. 

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5. Promoting solution-phase superlattices of CsPbBr ₃ nanocrystals

   https://doi.org/10.1039/D3NR00693J  

   Mireles_Villegas, Noel; Hernandez, Josue C.; John, Joshua C.; Sheldon, Matthew (June 2023, Nanoscale)

   We present a size-selective method for purifying and isolating perovskite CsPbBr 3 nanocrystals (NCs) that preserves their as-synthesized surface chemistry and extremely high photoluminescence quantum yields (PLQYs). The isolation procedure is based on the stepwise evaporation of nonpolar co-solvents with high vapor pressure to promote precipitation of a size-selected product. As the sample fractions become more uniform in size, we observe that the NCs self-assemble into colloidally stable, solution-phase superlattices (SLs). Small angle X-ray scattering (SAXS) and dynamic light scattering (DLS) studies show that the solution-phase SLs contain 1000s of NCs per supercrystal in a simple cubic, face-to-face packing arrangement. The SLs also display systematically faster radiative decay dynamics and improved PLQYs, as well as unique spectral absorption features likely resulting from inter-particle electronic coupling effects. This study is the first demonstration of solution-phase CsPbBr 3 SLs and highlights their potential for achieving collective optoelectronic phenomena previously observed from solid-state assemblies. 

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