Research Team Led by Ok Kang-min, Professor in the Department of Chemistry, Publishes Paper in JACS, one of the World’s Most Prestigious Academic Journals
A research team led by Professor Ok Kang-min in the Department of Chemistry has proposed a new inorganic crystal design strategy for achieving ultra-high-performance birefringence in the short-wavelength ultraviolet (SWUV) region and has successfully developed a new material with world-class performance.
Professor Ok Kang-min served as the corresponding author and postdoctoral researcher Chen Chong-An as the first author for this study. The research findings were published in the Journal of the American Chemical Society (JACS), the most prestigious academic journal in the field of chemistry.
Birefringence is a phenomenon where light travels at different speeds depending on its polarization direction as it passes through a material, enabling precise control over the direction, speed, and polarization state of light. This property serves as a core foundation for advanced optical technologies, including lasers, semiconductor lithography, optical communications, and precision sensors. However, in the short-wavelength ultraviolet region, developing high-performance birefringent materials has long been a major challenge due to the fundamental difficulty of simultaneously achieving a wide bandgap and high optical anisotropy.
To overcome these limitations, the research team proposed a new design strategy called “density-compensated polarizability anisotropy.” Unlike existing approaches that merely focus on increasing the anisotropy of individual structural units, this strategy maximizes macroscopic optical anisotropy by densely aligning small, linear anions.
Based on this, the research team designed and synthesized four new inorganic crystals, K[Hg(NCO)2]Cl, K[Cd(NCO)3], K2[Hg(NCO)4], and K2[Cd(NCO)4], by combining the linear cyanate anion (NCO⁻) with d10 transition metals (Hg²⁺ and Cd²⁺).
These materials achieved record-breaking birefringence values of up to Δn ≃ 0.511 (@546 nm) while maintaining ultraviolet transparency in the 229–254 nm range (SWUV cutoff). In particular, compounds 3 and 4 exhibit the highest performance among SWUV inorganic birefringent crystals reported to date. The research shows that this enhancement stems not merely from changes in chemical composition, but from the combined effect of an ordered structural arrangement induced by the high-density integration of linear (NCO)⁻ units and d10 metal ions. Specifically, the structural synergy of "high density + aligned directionality" was revealed as the key mechanism for maximizing optical anisotropy.
Professor Ok Kang-min stated, “This study demonstrates how the ‘bandgap-anisotropy trade-off,’ a long-standing challenge in birefringent material design, can be overcome through structural design strategies.” He added, “We expect this to provide a new direction for the development of ultraviolet lasers, ultra-precision optical systems, and next-generation photonic materials.”
Supported by the Global Leader Grants from the National Research Foundation of Korea, this study holds great significance as it goes beyond the development of a specific material to present a universal design principle for optical materials using linear-structure functional units.
▶Title: Density-Compensated Polarizability Anisotropy for Record Birefringence in Short-Wavelength Ultraviolet Inorganic Crystals
▶Direct link to the paper: https://pubs.acs.org/doi/10.1021/jacs.5c23008
[Keyword]
Optical Materials, Laser Technology, Advanced Chemistry
[Summary]
Through advanced chemistry, Professor Ok Kang-min's team has developed a world-record optical material for short-wavelength ultraviolet light. This breakthrough, published in JACS, provides a new design strategy for inorganic crystals, paving the way for next-generation laser technology and high-precision semiconductor manufacturing.
Professor Ok Kang-min served as the corresponding author and postdoctoral researcher Chen Chong-An as the first author for this study. The research findings were published in the Journal of the American Chemical Society (JACS), the most prestigious academic journal in the field of chemistry.
Birefringence is a phenomenon where light travels at different speeds depending on its polarization direction as it passes through a material, enabling precise control over the direction, speed, and polarization state of light. This property serves as a core foundation for advanced optical technologies, including lasers, semiconductor lithography, optical communications, and precision sensors. However, in the short-wavelength ultraviolet region, developing high-performance birefringent materials has long been a major challenge due to the fundamental difficulty of simultaneously achieving a wide bandgap and high optical anisotropy.
To overcome these limitations, the research team proposed a new design strategy called “density-compensated polarizability anisotropy.” Unlike existing approaches that merely focus on increasing the anisotropy of individual structural units, this strategy maximizes macroscopic optical anisotropy by densely aligning small, linear anions.
Based on this, the research team designed and synthesized four new inorganic crystals, K[Hg(NCO)2]Cl, K[Cd(NCO)3], K2[Hg(NCO)4], and K2[Cd(NCO)4], by combining the linear cyanate anion (NCO⁻) with d10 transition metals (Hg²⁺ and Cd²⁺).
These materials achieved record-breaking birefringence values of up to Δn ≃ 0.511 (@546 nm) while maintaining ultraviolet transparency in the 229–254 nm range (SWUV cutoff). In particular, compounds 3 and 4 exhibit the highest performance among SWUV inorganic birefringent crystals reported to date. The research shows that this enhancement stems not merely from changes in chemical composition, but from the combined effect of an ordered structural arrangement induced by the high-density integration of linear (NCO)⁻ units and d10 metal ions. Specifically, the structural synergy of "high density + aligned directionality" was revealed as the key mechanism for maximizing optical anisotropy.
Professor Ok Kang-min stated, “This study demonstrates how the ‘bandgap-anisotropy trade-off,’ a long-standing challenge in birefringent material design, can be overcome through structural design strategies.” He added, “We expect this to provide a new direction for the development of ultraviolet lasers, ultra-precision optical systems, and next-generation photonic materials.”
Supported by the Global Leader Grants from the National Research Foundation of Korea, this study holds great significance as it goes beyond the development of a specific material to present a universal design principle for optical materials using linear-structure functional units.
▶Title: Density-Compensated Polarizability Anisotropy for Record Birefringence in Short-Wavelength Ultraviolet Inorganic Crystals
▶Direct link to the paper: https://pubs.acs.org/doi/10.1021/jacs.5c23008
[Keyword]
Optical Materials, Laser Technology, Advanced Chemistry
[Summary]
Through advanced chemistry, Professor Ok Kang-min's team has developed a world-record optical material for short-wavelength ultraviolet light. This breakthrough, published in JACS, provides a new design strategy for inorganic crystals, paving the way for next-generation laser technology and high-precision semiconductor manufacturing.