As shown in the microscope image taken under excitation light, many of the compounds synthesized in the search stage are a collection of particles with various luminescent properties. Since differences in luminescent color correspond to differences in materials, candidate particles are selected based on the luminescent color and particle shape information.
In order to handle a large number of candidate particles, particle recognition and emission spectrum measurement have also been automated, allowing for the rapid identification of particles with the desired properties. Selected particles are identified using single crystal X-ray structural analysis, and this has been automated, making it possible to develop new phosphors at a faster rate. Crystal structure analysis is possible even with particle sizes of just a few micrometers. No special crystal growth process is required, and new phosphor particles can be found among the products of general synthesis processes.
Advanced Phosphor Group
Group leader
Group members
AIM and GOAL
- Luminescent materials are one of key materials in solid state lighting and advanced flat panel displays that hold the promise of energy saving, environment friendliness and high quality.
Our group concerns itself with both fundamental and industrial research and development in the field of advanced luminescent materials for energy and environment related applications. - We are going to discover new highly efficient and reliable phosphors with promising luminescence properties and interesting crystal structures for those applications, by careful materials selection and synthetic strategies.
APPROACH
- New phosphors discovery：
A single-particle-diagnosis approach is used to search for luminescent materials with new crystal structure and promising properties. New phosphors are developed even from mixture powder. - Materials synthesis：
Several synthetic techniques, such as gas-pressure sintering, hot-isostatic pressing, gas reduction and nitridation, solution synthesis are applied to prepare phosphor powders.
FIG 1 A single particle diagnosis approach for high-speed discovery of novel phosphors
FIG 2 New phosphors discovered by a single particle diagnosis approach (crystal structure and appearance)
TAKEDA, Takashi / Group Leader
New phosphor discovery by analysis of one particle in the powder
Overview
Phosphors are used in a variety of fields, LED lighting and displays. In the next-generation lighting and displays, phosphors that exceeds existing performance are needed. To achieve significant performance improvements, new phosphors are needed, not just improvements on known phosphors. However, the search for new phosphors, which is carried out by powder synthesis, is difficult because it requires single-phase powder.
By focusing on single particle in a mixture powder, new phosphors can be developed rapidly without single-phase synthesis.
Characteristics
- New phosphor discovery from the crystal structure and luminescence property analyses of one particle down to few microns
- New phosphor discovery from a mixture powder
- Development of the evaluation method of one particle phosphor
Major reserch
The luminescence characteristics of the particle can be evaluated in the same way as powder (excitation and emission spectra, temperature dependence, quantum efficiency, fluorescence lifetime, etc).
We are also working to develop new, more efficient phosphors in collaboration with information science. Using this method, we will develop the phosphors necessary for next-generation lighting and displays.
Summary
High brightness laser lighting and next generation display are realized through the development of new phosphors with heat-resistant emission and narrow-band emission. Single particle diagnosis approach can be applied to different materials by developing characterization method.
NAKANISHI, Takayuki
Development of Advanced phosphors for next-generation light source devices
Overview
Fluorescent materials that absorbed high-energy light or X-rays convert them into “luminescence” are key materials for national optical industry. In recent years, new fluorescent materials are required for various applications such as displays, wavelength conversion materials for µLEDs, and medical devices. We already have developed a number of “Ceramic-” and “Inorganic-organic hybrid-” phosphors with transition metals and lanthanides as luminescent centers, and have accelerated the science and technology of these materials. In industrial collaboration, we are focusing on contributing to society through joint development by identifying specific corporate demands.
Currently, we are focusing on (1) “ultra-broadband near-infrared LEDs,” which are important as analytical light, and (2) “practical applications of high-brightness nano-phosphors” for min/micro-LEDs. Here, we are expecting approaches from industry and academia.
Characteristics
- Development of various phosphors in the 400-1500nm range with world-leading Internal/External quantum efficiency
- Realization of broad near-infrared LED devices with long-time light source stability
- Development of narrow-line nanophosphors (emission width < 10nm) that can be excited in the UV-blue band
Major reserch 1
The Development of a Novel Near-Infrared Phosphor：
Advances in blue LED technology in industry and academia have evolved into laser diodes that induced more than a watt (W) of light with a millimeter-sized chip. In addition, semiconductor printing technology enables devices to be made so small that they are invisible to the eye. Phosphors have similarly advanced to a new stage, and in this research, we are developing new phosphors targeting near-infrared emission at 700-1800 nm, which is especially useful for sensor light sources, security, and biological applications. In order to realize the development goal of an ultra-white LED light source with high efficiency and face emission, it is essential to have practical multiple phosphors in each wavelength band.
The “quality” of light required for each need is different these days, and close collaboration with industry and academia is important for specific applications, and we look forward to receiving your requests.
Major reserch 2
Development of Highly Brilliant Coordination Phosphors and its Industrial Applications：
Luminescence intensity is the product of a material's light absorption ability and photo-conversion efficiency. However, no matter how good the two are, if the material stability and thermal/light durability are low, it will not become a real applied material.
This research aims to create specific lanthanide coordination phosphors designed at the molecular level by making full use of the basic science of inorganic and organic chemistry. Coordination phosphors are composed of rare earths as luminescent centers and organic ligands that form a structure and serve as optical antennas. By assembling each part like Lego blocks, it is possible to create original phosphors with new functions. These phosphors are expected to be used in next-generation transparent displays and micro-LEDs because of their strong optical absorption and the advantage of being dispersible in organic binders.
Summary
In this research, we are developing special phosphors with unique characteristics such as strong, broad, and narrow luminescence in the visible and near-infrared bands. We can provide material development that flexibly responds to social needs by designing phosphor materials with the keywords of “high brightness luminescence” and “practical materials".
Fields of Electronic and Photofunctional Materials Research Center
Ultra-wide Bandgap Semiconductors Group
Optical Single Crystals Group