Janke Eric M, Williams Nicholas E, She Chunxing, Zherebetskyy Danylo, Hudson Margaret H, Wang Lili, Gosztola David J, Schaller Richard D, Lee Byeongdu, Sun Chengjun, Engel Gregory S, Talapin Dmitri V
Department of Chemistry and James Franck Institute , University of Chicago , Chicago , Illinois 60637 , United States.
Materials Sciences Division , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States.
J Am Chem Soc. 2018 Nov 21;140(46):15791-15803. doi: 10.1021/jacs.8b08753. Epub 2018 Nov 7.
The ensemble emission spectra of colloidal InP quantum dots are broader than achievable spectra of cadmium- and lead-based quantum dots, despite similar single-particle line widths and significant efforts invested in the improvement of synthetic protocols. We seek to explain the origin of persistently broad ensemble emission spectra of colloidal InP quantum dots by investigating the nature of the electronic states responsible for luminescence. We identify a correlation between red-shifted emission spectra and anomalous broadening of the excitation spectra of luminescent InP colloids, suggesting a trap-associated emission pathway in highly emissive core-shell quantum dots. Time-resolved pump-probe experiments find that electrons are largely untrapped on photoluminescence relevant time scales pointing to emission from recombination of localized holes with free electrons. Two-dimensional electronic spectroscopy on InP quantum dots reveals multiple emissive states and increased electron-phonon coupling associated with hole localization. These localized hole states near the valence band edge are hypothesized to arise from incomplete surface passivation and structural disorder associated with lattice defects. We confirm the presence and effect of lattice disorder by X-ray absorption spectroscopy and Raman scattering measurements. Participation of localized electronic states that are associated with various classes of lattice defects gives rise to phonon-coupled defect related emission. These findings explain the origins of the persistently broad emission spectra of colloidal InP quantum dots and suggest future strategies to narrow ensemble emission lines comparable to what is observed for cadmium-based materials.
尽管胶体InP量子点的单粒子线宽与镉基和铅基量子点相似，并且在改进合成方法方面投入了大量努力，但其整体发射光谱仍比镉基和铅基量子点所能达到的光谱更宽。我们试图通过研究负责发光的电子态的性质来解释胶体InP量子点持续存在的宽发射光谱的起源。我们发现发光InP胶体的发射光谱红移与激发光谱的异常展宽之间存在相关性，这表明在高发射率的核壳量子点中存在与陷阱相关的发射途径。时间分辨泵浦 - 探测实验发现，在光致发光相关的时间尺度上，电子基本上没有被困住，这表明是局域化空穴与自由电子复合产生的发射。对InP量子点进行的二维电子光谱揭示了多个发射态以及与空穴局域化相关的电子 - 声子耦合增加。假设价带边缘附近的这些局域化空穴态是由与晶格缺陷相关的不完全表面钝化和结构无序引起的。我们通过X射线吸收光谱和拉曼散射测量证实了晶格无序的存在及其影响。与各类晶格缺陷相关的局域电子态的参与导致了声子耦合的缺陷相关发射。这些发现解释了胶体InP量子点持续宽发射光谱的起源，并提出了未来使整体发射线变窄的策略，使其与镉基材料所观察到的情况相当。
