Efficient Rare-Metal-Free Phosphorescent Molecule Discovered

Guest Authors July 29, 2024

By Dr. Jonathan Melman & David Shiller

Japanese researchers led by Osaka University have published the discovery of a family of significantly more efficient organic, rare-metal-free, phosphorescent materials: thienyl diketones. Room temperature phosphorescence (RTP) without using rare metals has been an area of intense research. Most commercial RTP materials today utilize iridium or platinum, both rare metals with high costs. RTP materials are currently used in OLEDs and cancer diagnostics.

Several thienyl diketone compounds were tested in various states (liquid, crystalline solids, polymer films). The materials exhibited narrow spectrum emissions in the 560 – 568 nm range (yellow). The researchers achieved RTP quantum yields (efficiencies) of 38.2% in solution under Ar, 54% in a polymer matrix in air, and 50% in crystalline solids in air.

The material discovery and new design guidelines for developing organic, rare metal-free phosphorescent materials have the potential to lead to significant advancements in lighting, OLEDs, and medical diagnostics.

David Shiller asked Dr. Jonathan Melman, an expert in phosphors and other downconverters, about the significance of this research. Dr. Melman shared:

The narrow emissions (FWHM) is good for display applications.
The 560-568nm wavelength is not good for RGB displays. If the researchers could adjust the wavelength to 540nm it would be good for displays utilizing the DCI-P3 gamut.
In theory, the 560nm could be paired with a blue pump for lighting to create 4000K-5000K CCT, but the narrow emissions would create a terribly low CRI.
It could find positive use in OLED general illumination using 4 narrow emissions, such as RGBY.
The design rules created by the team could lead to further discoveries and improvements in the rare-metal-free thienyl diketone. It’s also a positive that they emit well under different physical conditions: solid material, in liquid solution, and in polymer film.
With time, the researchers may be able to shift the emission wavelengths to those more appropriate for display, both green and red. By doing the detailed mechanistic work, they have a better chance of getting large shifts to the wavelengths they want, and not necessarily just incremental changes to a material that seems to somewhat work.
A major question is that OLEDs are not photoluminescence (PL) driven, but electroluminescence (EL) driven. How will the material perform under those EL conditions?

The full research paper can be found here. Special thanks to Dr. Melman for sharing his downconverter expertise with LightNOW readers.

About The Authors

Dr. Jonathan Melman is Principal & CTO of Melman Consulting, LLC, which provides Chemistry, IP, and Business Services to Small Businesses and Start-ups – Especially focusing on the LED, Lighting, and Display industries. Dr. Melman’s specialties include: Solid State Lighting/Phosphor Converting LEDs, Rare Earth Chemistry, Coordination Chemistry, and Government Research Contracts.

David Shiller is Publisher of LightNOW and President of Lighting Solution Development, a leading business development and marketing consulting firm to the lighting, EV charger, and networked lighting control industries.