Nanotechnologies / Materials
Display, Lighting, Bioimaging

Synthesis and functionalization of colloidal quantum dots
Department of Applied Chemistry, Graduate School of Engineering
Associate Professor Taro Uematsu
https://researchmap.jp/t-uematsu?lang=en

Abstract
Semiconductor nanoparticles (quantum dots) are chemicallysynthesized colloidal fluorophores characteristic of monochromaticluminescence. Both particle size and composition affect the energy
structure and emission color of quantum dots, attracting significant
attention as new materials for future optical devices. Aiming atquantum dot devices, we continue the development of environmentally benign quantum dots and functionalization by designing
the surrounding environment.

the MOF to the quantum dot occurred, doubling the photoluminescence intensity of the quantum dots.

Nanotechnologies / Materials▍ Background & Results
Embedding quantum dots in matrices is essential for demonstrating high-performance quantum dot devices by facilitating
the injection of charge and energy. In particular, with the ongoingdevelopment of quantum dot LEDs, which are self-luminous devices similar to OLEDs, new ideas for utilizing quantum dots withoutcompromising their properties are strongly required.

Spectrally narrow band-edge photoluminescence from AgInS2 quantum dots by
the coating with GaSx shell▍ Significance of the research and Future perspective
The development of quantum dots originates from a weak fluorescence from nano-sized semiconductors over 30 years ago.
Since then, the quantum dots have been improved to the point thatthey are used in commercial displays as wavelength conversion
materials. Until a few years ago, the optically superior quantum
dots were cadmium compounds, but their use in consumer products has encouraged the development of low-toxic alternatives.
Our group developed photoluminescent AgInS2 quantum dots andtheir analogs composed of three or more elements. However, theobtained photoluminescence was “defect emission” with a broad
spectral width. Despite attempts by many researchers to narrow
the spectral width, it had been impossible for several years, making researchers consider the band-edge emission hopeless. Under
such situations, we focused on the surface condition and coatedAgInS2 quantum dots with gallium sulfide, an unconventional material as the shell. We eliminated surface defect levels and obtaineda spectrally narrow band edge emission comparable to cadmium
compound quantum dots in yellow region. We further demonstrated the green and red luminescence, which is more valuable as
fluorescent materials, by alloying the core semiconductors to tune
their bandgap.
It is crucial to design matrices to manipulate the excitation energy of quantum dots. As a first step toward this goal, we used metal-organic frameworks (MOFs), which have a highly ordered structure and grow under mild conditions. Since the lattice size of MOFs
is smaller than the diameter of quantum dots, we have attempted
to create composite materials by growing MOFs from the surfaceof quantum dots. Using a typical MOF, ZIF-8, an ultimate structurethat contains a single quantum dot at the center of a polyhedral
MOF crystal was obtained. When a red-emitting quantum dot wasincorporated in a blue-emitting IRMOF-3, the energy transfer fromQuantum dot–MOF complex fabricated by growing MOF from the surface of thequantum dots. Energy transfer was demonstrated by embedding red-emission
quantum dot into blue-emission MOF.

Green-color emission from cadmium-free quantum dots by alloying AgInS2 coresto increase their bandgap.

P a t e n t Japanese Patent Application No. 2017-037487, Japanese Unexamined Patent Publication No. 2018-044142, Japanese Patent No. 6464215
Kumagai, Kohei; Uematsu, Taro; Kuwabata, Susumu et al. Photoluminescence Enhancement by Light Harvesting of Metal–Organic Frameworks
Surrounding Semiconductor Quantum Dots, Chem. Mater., 2021, 33(5), 1607–1617. doi: 10.1021/acs.chemmater.0c03367
Watcharaporn Hoisang, Uematsu, Taro; Kuwabata, Susumu et al. Luminescent Quaternary Ag(InxGa1−x)S2/GaSy Core/Shell Quantum Dots
T r e a t i s e Prepared Using Dithiocarbamate Compounds and Photoluminescence Recovery via Post Treatment, Inorg Chem, 2021, 60, 13101–13109.
doi: 10.1021/acs.inorgchem.1c01513
Uematsu, Taro; Wajima, Kazutaka; Kuwabata, Susumu et al. Narrow Band-Edge Photoluminescence from AgInS2 Semiconductor Nanoparticles by theFormation of Amorphous III-VI Semiconductor Shells, NPG Asia Materials, 2018, 10, 713–726. doi: 10.1038/s41427-018-0067-9
URLK e y w o r d quantum dots, cadmium-free, fluorophores