Establishment of absolute photoluminescence (PL) quantum yield measurement method and research on organic optoelectronics

Published June 10, 2025

The Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, is engaged in the research and development of next-generation organic semiconductor devices, including organic light-emitting diode (OLED) devices. In 2012, they succeeded in creating the world's first 3rd-generation organic electroluminescence (EL) emission material called Thermally Activated Delayed Fluorescence (TADF) molecules, leading the field of organic optoelectronics research. Various measurement methods are required to evaluate organic optoelectronic materials and devices, including PL quantum yield measurements and transient luminescence characteristic measurements. For these evaluations, they have used our Quantaurus series and streak cameras.

We interviewed Prof. Chihaya Adachi, Director of the Center, and Assoc. Prof. Hajime Nakanotani about establishing absolute photoluminescence quantum yield measurement methods, the impact of our Quantaurus series on their research, and their prospects for future research.

About research
Background to the establishment of the PL quantum yield measurement method for solids
Impact on research after establishment of absolute PL quantum yield measurement method
Hamamatsu Photonics products in fluorescence lifetime measurement
Measurement example
Research prospects
About Kyulux, Inc.
About KOALA Tech Inc.
Researcher profiles

About research

Could you tell us about your research and background?

Prof. Adachi: Our center researches organic optoelectronics, including OLEDs, and develops new semiconductor materials, new device structures based on these materials, and new devices. In 2012, our group succeeded in the world's first creation of TADF molecules, the 3rd generation of organic electroluminescent materials. In 2015, we launched a start-up company (Kyulux) to develop light-emitting devices based on this technology. In 2019, KOALA Tech, Inc. was established to commercialize the organic semiconductor laser diode, which was also successfully developed by the center as a world pioneer. We currently work as a technical advisor to these companies in commercializing and mass-producing materials and devices.

I have been consistently researching OLEDs since around 1987, when I was a graduate student. At that time, there were only a few OLED researchers worldwide. But I believed that challenging a subject that no one else was doing would be of great value. After my graduate studies, I joined a manufacturer and continued my research. A major turning point was research on phosphorescence in the laboratory of Dr. Stephen R. Forrest at Princeton University, to which I later transferred. It was here that the development of OLEDs using second-generation phosphorescent materials began, and by around 2000, I could increase the conversion efficiency to almost 100%.

After that, I returned to Japan and continued researching at Chitose University of Science and Technology. There, I decided to create a new material that would be competitive with phosphorescent materials and succeeded in developing the TADF material. The advantage of this material is that it does not use rare metals, so it can make OLED devices at a lower cost than devices using second-generation phosphorescent materials. Currently, we are working on the practical application of devices based on this TADF material and the research and development of various materials and devices other than OLEDs, such as perovskite solar cells and organic laser diodes.

Professor Chihaya Adachi

Associate Professor Hajime Nakanotani

Background to the establishment of the PL quantum yield measurement method for solids

One method for evaluating luminescent materials, such as OLEDs, is to measure PL quantum yields. However, I understand that this measurement method was not established then. Could you explain how the current PL quantum yield measurement method was established?

Prof. Adachi: At that time, various measurement methods for PL quantum yields of solid materials were reported in the literature. However, the PL quantum yield values varied significantly across different publications, even for the same sample, and there was no established standard method. The only established method was the 'relative method', which involved measuring a standard solution with known PL quantum yield and a sample solution with unknown quantum yield under identical conditions, then comparing these values to determine the relative PL quantum yield of the sample solution. However, this method was limited to measuring solutions and could not be used to evaluate solid materials such as OLEDs.

Under these circumstances, in our laboratory, Dr. Yuichiro Kawamura, a researcher in the JST CREST project, led the development of a measurement system that combined an integrating sphere method reported in the literature with a Hamamatsu Photonics spectrometer (PMA-10). Subsequently, we collaborated with Hamamatsu Photonics to develop an absolute PL quantum yield measurement system. To validate this system, we worked jointly with Hamamatsu Photonics and Tobita Laboratory (currently the Yoshihara Laboratory) at Gunma University to measure the PL quantum yields of fluorescence standard solutions. This helped establish the reliability of the measurements obtained through this method. As a result, we successfully established the 'absolute photoluminescence quantum yield method using an integrating sphere,' enabling solid materials measurement.

Publications：Y. Kawamura, H. Sasabe, C. Adachi, Jpn. J. Appl. Phys., 43, 7729 - 7730 (2004).

A. Endo, K. Suzuki, T. Yoshihara, S. Tobita, M. Yahiro, and C. Adachi, Chem. Phys. Lett., 460, 155–157 (2008).

Impact on research after establishment of absolute PL quantum yield measurement method

What impact did establishing the absolute photoluminescence quantum yield measurement method have on research? Additionally, how has our Quantaurus-QY^® been beneficial to the research?

Prof. Adachi: The most significant impact of establishing the PL quantum yield measurement method is that the luminescence quantum yield values can now be measured correctly. Combining with the value of PL quantum yield and fluorescence lifetime measurements has made it possible to correctly calculate the value of a material's luminescence properties (emission rate constant: kr). As a result, a more detailed characterization of the material is now possible, and the reliability of the characterization has been improved.

Quantaurus-QY is used in the OPERA

Usage image of Quantaurus-QY

Dr. Nakanotani: From the perspective of promoting research, the three most significant impacts were 1) reduction of measurement time, 2) standardization of work, and 3) reduction of measurement and calculation errors.

Regarding measurement time, the procedure has become simpler compared to the relative method, allowing us to reduce the measurement time.

The procedure has become so simple that anyone can easily perform the measurements by placing the sample in the integrating sphere and taking the measurement, not limited to specialized engineers. Additionally, in the early stages of developing this method, we manually calculated the PL quantum yield values from the spectra obtained by the spectrometer. However, the dedicated software developed by Hamamatsu Photonics to automate PL quantum yield calculation reduced the risk of calculation errors.

Prof. Adachi: The ease of measurement is a very good thing from the perspective of promoting research. However, there are some concerns from the perspective of educating students and researchers. Because anyone can make measurements simply by pushing a button on the device, it is not good for students and researchers to proceed with their research without understanding the mechanisms of measurement, etc. Therefore, we strive to ensure that students and researchers understand these basics before using the device.

Hamamatsu Photonics products in fluorescence lifetime measurement

The Center for Organic Photonics and Electronics Research (OPERA) also uses the Quantaurus-Tau® compact fluorescence lifetime measurement system and streak cameras to measure materials' fluorescence lifetime and transient absorption.

Quantaurus-QY is used in the OPERA

Usage image of Quantaurus-Tau

Streak camera is used in the OPERA

Usage image of Streak camera

Measurement example

Quantum yield measurement of thermally activated delayed fluorescent materials with high luminous efficiency

Thermally activated delayed fluorescence (TADF) materials are well known as third-generation OLED materials. TADF is the fluorescence generated by the reversed intersystem crossing process (RISC) from the lowest triplet to the singlet states, and the RISC is promoted by the small energy gap between the lowest excited states (ΔEST). A novel TADF material (4CzIPN) was successfully developed by precise molecule design. The material has a small ΔEST, and it shows a high PL quantum yield of 0.94 +/- 0.02.

Quantum yield measurement of TADF materials

Data courtesy of Prof. Chihaya Adachi, Hajime Nakanotani, Center for Organic Photonics and Electronics Research (OPERA), Kyushu University.

Publication: H. Uoyama, K. Goushi, K. Shizu, H. Nomura, and C. Adachi, Nature, 492, 234-238 (2012).

Efficient Near-Infrared Fluorescence in Deuterated Host–Guest System for Near-Infrared Organic Light-Emitting Diodes

PL quantum yield (left) and fluorescence lifetime measurement (right) of near-infrared fluorochromes.

Deuterium substitution increases the PLQY of the NIR fluorophore from 7 % to 15 %.

Data courtesy of: Prof. Chihaya Adachi, Hajime Nakanotani, Center for Organic Photonics and Electronics Research (OPERA), Kyushu University.

Publication: Q. Yu, Y. Tamura, H. Nakanotani, M. Mamada, C. Adachi, Adv. Optical Mater. 2024, 12, 2400932.

Research prospects

Could you tell us about your research prospects?

Prof. Adachi: We are currently focusing not only on research and development related to OLEDs but also on developing organic solar cells using perovskite and devices using organic charge transfer (CT) complexes. We have been exploring the potential of organic semiconductor devices for many years, and recently, we succeeded in developing a novel organic thermoelectric conversion device that can convert small thermal energy of about tens of meV at room temperature in everyday environments into electricity.

In recent years, the effective use of renewable and unused energy has been sought worldwide. Although thermoelectric conversion devices utilizing waste heat have been partially commercialized, their use remains limited due to various issues. This device, which converts small amounts of thermal energy present at room temperature into electricity, holds the potential to solve energy problems. We consider it a significant achievement of our research that we can now offer this new energy conversion tool to society. Moving forward, we aim to improve the device's performance and stability and pave the way for its practical application.

Publication: S. Kondo, M. Kameyama, K. Imaoka, Y. Shimoi, F. Mathevet, T. Fujihara, H. Goto, H. Nakanotani, M. Yahiro, and C. Adachi, Nat. Commun., 15, 8115 (2024).

Dr. Nakanotani: I have recently become interested in materials and devices that emit near-infrared light. Currently, OLEDs are mainly used in the display field, but I would like to create devices that can be used as near-infrared light sources for sensing applications. If we can apply OLEDs to sensors and light sources using near-infrared light, I believe it will lead to business opportunities.

Professor Chihaya Adachi and Associate Professor Hajime Nakanotani

About Kyulux, Inc.

Kyulux, Inc., is a startup company from Kyushu University, established in 2015. It is working on commercializing the OLED technology "Hyperfluorescence™" for use in OLED displays and lighting. Hyperfluorescence™ developed at the Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, is highly anticipated by the display industry as the ultimate OLED technology that achieves high efficiency and high color purity without using rare metals.

Additionally, to accelerate the development of TADF, Kyumatic™, a Materials Informatics (MI) system that combines cutting-edge artificial intelligence (AI) with unique functions introduced by Harvard University in 2016, was applied to materials development to increase development speed dramatically. Kyumatic™ can not only predict material properties but also predict the performance of thin films and devices, and we are focusing on technological development not only for material development and mass production but also for the future development of organic optoelectronic materials.

Prof. Adachi: The Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, is involved in supporting the research and development of Kyulux and is working on high-speed spectroscopic and theoretical analysis of excited states in CT molecular systems, as well as clarification of device degradation mechanisms, to deepen the scientific principles and propose high-performance molecules. We strongly expect that this basic research will improve practical device performance.

Explore the website of Kyulux, Inc.

About KOALA Tech Inc.

KOALA Tech, Inc., is a start-up company from Kyushu University, established in 2019. This company was established to commercialize the world's first Organic Semiconductor Laser Diode (OSLD) laser technology realized by the Kyushu University Research Center for Advanced Organic Photonics and Electronics (OPERA). OSLDs combine the “flexibility, low environmental impact, low cost, and high wavelength selectivity” of organic electronics with the “high color purity and high light linearity” of lasers.

We have been working on the practical application of OSLDs as a laser light source that is highly compatible with organic electronic device platforms, including OLEDs, which have attracted attention in recent years as high-definition and flexible displays to provide new solutions to customers in the organic semiconductor device field and to contribute to a smart society where people and technology coexist through organic x laser hybrid technology.

Prof. Adachi: The Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, provides cutting-edge academic knowledge and world-class research and development infrastructure through its collaborative research with KOALA Tech. We expect that further advancements and commercialization of organic semiconductor laser research and development will significantly expand the frontier of organic electronics in both academic and industrial fields.

OSLD device structure

Explore the website of KOALA Tech, Inc.

Researcher profiles

Professor Chihaya Adachi

Chihaya Adachi
Department of Applied Chemistry, Kyushu University: Professor
Center for Organic Photonics and Electronics Research (OPERA): Director

Mar. 1991

Ph.D., Department of Materials Development Engineering, Graduate School of Engineering Sciences, Kyushu University

Apr. 1991

Researcher, Ricoh Co., Ltd. Chemical Products Technology Research Institute

Aug. 1996

Assistant, Department of Functional Polymer Science, Faculty of Textile Science and Technology, Shinshu University

May. 1999

Researcher, Center for Photonics and Optoelectronic Materials (POEM), Princeton University

Mar. 2001

Assistant Professor, Department of Materials and Photonic Science, School of Photonics Science, Chitose Institute of Science and Technology

Apr. 2004

Professor, Department of Materials and Photonic Science, School of Photonics Science, Chitose Institute of Science and Technology

Oct. 2005

Professor, Center for Future Chemistry, Kyushu University

Apr. 2010

Current post

Associate Professor Hajime Nakanotani

Hajime Nakanotani
Department of Applied Chemistry, Kyushu University: Associate Professor
Center for Organic Photonics and Electronics Research (OPERA): Vice Director

Mar. 2010

Department of Materials Creation Engineering, Graduate School of Engineering, Kyushu University, Ph.D.

Apr. 2010

Researcher, Ricoh Co., Ltd. Research and Development Headquarters

Apr. 2012

Researcher, Organic Photonics Device Laboratory, Kyushu Institute of Advanced Science and Technology, Public Interest Incorporated Foundation
Visiting Assistant Professor, Center for Futere Chemistry

Apr. 2014

Assistant Professor, Center for Organic Photonics and Electronics Research (OPERA)

Jan. 2015

Department of Applied Chemistry, Kyushu University: Associate Professor

Apr. 2019

Center for Organic Photonics and Electronics Research (OPERA): Vice Director

Explore the website of the Center for Organic Photonics and Electronics Research (OPERA), Kyushu University

Related product

Quantaurus-QY^® Absolute PL quantum yield spectrometer

Compact one-box absolute quantum yield spectrometer for luminescence materials using photoluminescence method. Not only thin materials but also liquid solution and powder can be analyzed. It quickly measures the absolute PL quantum yield, excitation wavelength dependence and PL in a short time.

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