Schneider R, Weigert F, Lesnyak V, Leubner S, Lorenz T, Behnke T, Dubavik A, Joswig J-O, Resch-Genger U, Gaponik N, Eychmüller A
Federal Institute for Materials Research and Testing (BAM), Richard-Willstätter-Str. 11, 12489 Berlin, Germany.
Phys Chem Chem Phys. 2016 Jul 28;18(28):19083-92. doi: 10.1039/c6cp03123d. Epub 2016 Jun 30.
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.
半导体纳米晶体（SC NCs）的光学性质在很大程度上受其尺寸和表面化学性质的控制，即无机钝化壳的化学成分和厚度、表面配体的化学性质和数量以及它们与表面原子键合的强度。后者对于CdTe纳米晶体尤为重要，CdTe纳米晶体与合金化的CdxHg1-xTe一起，是仅有的能够在水中高质量制备且无需额外无机钝化壳的SC NCs。为了更好地理解稳定配体对控制SC NCs与应用相关的荧光特性的作用，我们评估了两种最常用的单齿硫醇配体，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表面原子配位键强度的间接测量方法，在水和重水中研究了pH（pD）和浓度对这些胶体PL性质的影响，并与之前在重水中对一组硫醇封端的Cd1-xHgxTe SC NCs进行稀释研究的结果进行了比较。作为这些研究的前提条件，在SC NC合成后，使用埃尔曼测试在不同纯化步骤中通过光度法测定表面配体的数量。我们的结果表明，这些SC NCs的pH依赖性PL受配体控制，MPA稳定的CdTe NCs比TGA封端的更不易发生发光猝灭。对于两种类型的CdTe胶体，与重水相比，在水中配体解吸更明显，这也突出了氢键和溶剂分子的作用。
