pH and concentration dependence of the optical properties of thiol-capped CdTe nanocrystals in water and D2O.
pH and concentration dependence of the optical properties of thiol-capped CdTe nanocrystals in water and D2O.
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DOI：
10.1039/c6cp03123d
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发表时间：
2016-07
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通讯作者：
R. Schneider;F. Weigert;V. Lesnyak;S. Leubner;T. Lorenz;T. Behnke;A. Dubavik;Jan‐Ole Joswig;U. Resch‐Genger;N. Gaponik;A. Eychmüller
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作者：
R. Schneider;F. Weigert;V. Lesnyak;S. Leubner;T. Lorenz;T. Behnke;A. Dubavik;Jan‐Ole Joswig;U. Resch‐Genger;N. Gaponik;A. Eychmüller
半导体纳米晶体（SC NC）的光学性质主要由其尺寸和表面化学控制，即，无机钝化壳的化学组成和厚度以及表面配体的化学性质和数量以及它们与表面原子的键合强度。后者对于CdTe NC尤其重要，其与合金化CdxHg 1-xTe一起是唯一可以在水中以高质量制备而不需要额外的无机钝化壳的SC NC。为了更好地理解稳定配体的作用，用于控制SC NC的应用相关的荧光特性，我们评估了两种最常用的单齿巯基配体，巯基乙酸（TGA）和巯基丙酸（MPA），对一组CdTe NC胶体的胶体稳定性，光致发光（PL）量子产率（QY）和PL衰减行为的影响。作为配体与SC NC表面原子的配位键强度的间接测量，在水和D2 O中检查了pH（pD）和浓度对这些胶体的PL性质的影响，并与之前使用一组巯基封端的Cd 1-xHgxTe SC NC在D2 O中稀释研究的结果进行了比较。作为这些研究的先决条件，在SC NC合成后用Ellman试验在不同的纯化步骤中光度测定表面配体的数量。我们的研究结果表明，这些SC NC的pH依赖性PL的配体控制，MPA稳定的CdTe NC比TGA封端的发光淬灭的倾向更小。对于这两种类型的碲化镉胶体，配体解吸是更明显的H2O相比，D2 O，也强调氢键和溶剂分子的作用。
The optical properties of semiconductor nanocrystals (SC NCs) are largely controlled by their size and surface chemistry, i.e., the chemical composition and thickness of inorganic passivation shells and the chemical nature and number of surface ligands as well as the strength of their bonds to surface atoms. The latter is particularly important for CdTe NCs, which - together with alloyed CdxHg1-xTe - are the only SC NCs that can be prepared in water in high quality without the need for an additional inorganic passivation shell. Aiming at a better understanding of the role of stabilizing ligands for the control of the application-relevant fluorescence features of SC NCs, we assessed the influence of two of the most commonly used monodentate thiol ligands, thioglycolic acid (TGA) and mercaptopropionic acid (MPA), on the colloidal stability, photoluminescence (PL) quantum yield (QY), and PL decay behavior of a set of CdTe NC colloids. As an indirect measure for the strength of the coordinative bond of the ligands to SC NC surface atoms, the influence of the pH (pD) and the concentration on the PL properties of these colloids was examined in water and D2O and compared to the results from previous dilution studies with a set of thiol-capped Cd1-xHgxTe SC NCs in D2O. As a prerequisite for these studies, the number of surface ligands was determined photometrically at different steps of purification after SC NC synthesis with Ellman's test. Our results demonstrate ligand control of the pH-dependent PL of these SC NCs, with MPA-stabilized CdTe NCs being less prone to luminescence quenching than TGA-capped ones. For both types of CdTe colloids, ligand desorption is more pronounced in H2O compared to D2O, underlining also the role of hydrogen bonding and solvent molecules.