Research Institute for Electronic Science, Hokkaido University


LAST UPDATE 2017/02/25

  • 研究者氏名
    Researcher Name

    ビジュヴァスデヴァンピライ BIJU Vasudevan Pillai
    教授 professor
  • 所属
    Professional Affiliation

    Research Institute for Electronic Science, Hokkaido University

    Laboratory of Molecular Photonics
  • 研究キーワード
    Research Keywords

    Semiconductor nanoparticles
    Electron and energy transfer dynamics
    Photo-functional molecules and nanomaterials
    Fluorescent molecular- and nano-sensors
Research Subject

Photoluminescence of highly-excited semiconductor nanoparticles

研究の背景 Background

The unparalleled optical properties of semiconductor quantum dots present enormous opportunities - from optoelectronic devices to single photon sources. Stable emission of photoluminescence is an essential element for such applications. Nonetheless, like organic dye molecules, semiconductor quantum dots suffer from photo-oxidation, which challenges the durability of quantum dot devices. Despite the unique size-dependent tunable and bright photoluminescence of quantum dots, these nanocrystals at single-particle level suffer from unpredictable intensity loss, which is contributed by the digitized (one-step) ON and OFF intermittency, also called blinking, and the non-digitized (gradual) photo-darkening. Blinking is due to Auger ionization and subsequently the carriers follow non-radiative carrier recombination in the trion state. During such blinking, the OFF state dominate until the ionized quantum dot is neutralized. On the other hand, photo-darkening is the result of irreversible self-sensitized surface oxidation. Therefore, rationalization of photoluminescence intensity loss in quantum dots is essential for the advancement of quantum dot technology.

研究の目標 Outcome

By analyzing the photoluminescence properties of CdSe/ZnS quantum dots at single molecule and ensemble levels, we prove that the non-digitized photoluminescence intensity loss in single quantum dots immersed in aerated solvents, which is due to oxidation by selfsensitized generation of singlet oxygen, is absent in highly-excited state or during the Auger-ionized OFF periods. In other words, irrespective of the Auger-ionized duration, the PL intensity of a QD after each intrinsic OFF period recovers to the same level as that before Auger ionization. We provide information about not only the roles of singlet oxygen on the gradual oxidation and the non-digitized photoluminescence intensity loss of single quantum dots but also the intrinsic stability of quantum dots by escape from oxidation into the Auger-ionized state. Rationalization of the escape of Auger-ionized quantum dots from photo-oxidation is expected to have an impact on the preparation of durable quantum dots for applications such as single photon devices and quantum dot-sensitized solar cells.

研究図Research Figure

Fig.1. Self-sensitized oxidation of a CdSe/ZnS quantum dot (top), and fluorescence of a mixture of a singlet oxygen sensor and quantum dots before and after sensitization (bottom). Fig.2. (A) Scheme of photo-oxidation and ionization of quantum dots. (B,C) Simulated photoluminescence intensity trajectories of a single quantum dot (B) under continuous oxidation and (C) under intermittent Auger ionization and oxidation

文献 / Publications

S. Yamashita, M. Hamada, S. Nakanishi, H. Saito, Y. Nosaka, S. Wakida, V. Biju, Angew. Chem. Int. Ed. 2015, 54, 3892-3896.
D. K. Sharma, S. Hirata, L. Bujak, V. Biju, T. Kameyama, M. Kishi, T. Torimoto, M. Vacha, Nanoscale 2016, 8, 13687-13694.