Research

Chalcohalides have emerged as promising materials for next-generation electronic and optoelectronic devices due to their unique electronic structures, high charge carrier mobility, defect tolerance, strong light absorption, and tunable optical and electrical properties. In particular, chalcohalide nanocrystals synthesized via solution-based fabrication methods exhibit excellent electrical and optical performance owing to their uniform size, shape, composition, and colloidal stability in various solvents. These characteristics make them highly suitable for solution-processable device fabrication, enabling low-cost and low-temperature manufacturing.

Our research group focuses on the solution-phase synthesis of novel metal chalcohalide nanocrystals and their applications in solution-processed optoelectronic devices. We are developing novel synthesis strategies such as solvothermal, hot-injection, and heat-up methods with precise control of phase and compositions, and conducting in-depth investigations into the structural and optical properties of chalcohalide nanocrystals. These help us understand the structure–property relationships and optimize the synthesis conditions for enhanced material performance. Furthermore, we investigate their integration into optoelectronic and photoelectrochemical devices, such as photodetectors and PEC cells, to fully exploit the advantages of these solution-processed nanocrystals. 

Our research laboratory focuses on the synthesis, structural characterization, and optical investigation of luminescent nanocrystals based on lanthanide elements and metal halide perovskite compounds. Lanthanide-based nanocrystals offer tremendous potential for emerging applications, including displays, spectral converters for photovoltaics, and optical sensors. The unique optical and magnetic properties of lanthanide ions arise from their partially filled 4f orbitals, which result in sharp atomic absorption and emission lines as well as exceptionally long excited-state lifetimes. By incorporating optically active lanthanide dopants into carefully engineered host matrices, we explore nonlinear optical processes such as upconversion luminescence, quantum cutting, and downshifting via energy transfer between discrete electronic states. By tailoring their composition, morphology, and surface chemistry, we aim to optimize their optical efficiency and integration into device platforms.

In parallel, our laboratory investigates all-inorganic metal halide perovskite or perovskite-related nanocrystals composed of non-toxic elements, as promising luminescent materials for optoelectronic applications. With appropriate compositions or doping, these perovskite NCs exhibit high photoluminescence quantum yields and narrow emission bandwidths, which can be precisely tuned by controlling their chemical composition, particle size, and structural dimensionality. These factors significantly affect their optical behavior, enabling tunable emission through both compositional and structural controls. This structural versatility makes them highly attractive for next-generation light-emitting and photonic applications. By combining advanced colloidal synthesis methods, comprehensive spectroscopic analyses, and systematic tuning of nanocrystal architecture, our laboratory aims to deepen the fundamental understanding of these material systems and to expand their practical applications in optoelectronics and energy conversion.

Our research group focuses on smart and reconfigurable materials for next-generation optical components and sustainable energy-saving systems. As a first step, we have developed thermochromic vanadium dioxide (VO₂) films from colloidally synthesized nanoparticles. VO₂ exhibits unique thermochromic properties, undergoing a reversible insulator–metal transition at a critical temperature (Tc ≈ 68 °C). Specifically, it transforms from the monoclinic insulating phase (VO₂(M), space group P2₁/c) to the metallic rutile phase (VO₂(R), space group P4₂/mnm). This phase transition is accompanied by remarkable changes in electrical and optical properties, which can be exploited for smart building blocks in reconfigurable optics. Moreover, during the transition, VO₂(M) maintains high near-infrared (NIR) transmittance, while VO₂(R) significantly suppresses NIR transmission, thereby enabling efficient regulation of solar heat gain without requiring external power input. These characteristics make VO₂-based films highly promising for energy-saving smart windows that adaptively control light and heat transmission, contributing to sustainable building technologies. 

In addition to thermochromic materials, our group also develops nanoparticle-based radiative cooling materials that passively dissipate heat to the cold universe, offering new opportunities for energy-efficient thermal management. Furthermore, we are investigating high-refractive-index nanocrystals tailored for advanced AR/VR optical components, aiming to enhance light manipulation and improve immersive display performance. Through these multidisciplinary approaches, our mission is to pioneer multifunctional materials that bridge sustainability and next-generation photonic technologies.