Kiyoshi Miyata

Hybrid lead halide perovskites exhibit carrier properties that resemble those of pristine nonpolar semiconductors despite static and dynamic disorder, but how carriers are protected from efficient scattering with charged defects and optical phonons is unknown. Here, we reveal the carrier protection mechanism by comparing three single-crystal lead bromide perovskites: CH₃NH₃PbBr₃, CH(NH₂)₂PbBr₃, and CsPbBr₃ We observed h

Lead halide perovskites show marked defect tolerance responsible for their excellent optoelectronic properties. These properties might be explained by the formation of large polarons, but how they are formed and whether organic cations are essential remain open questions. We provide a direct time domain view of large polaron formation in single-crystal lead bromide perovskites CH₃NH₃PbBr₃ and CsPbBr₃. We found that large polaron forms predominantly fro

Lead halide perovskites have been demonstrated as high performance materials in solar cells and light-emitting devices. These materials are characterized by coherent band transport expected from crystalline semiconductors, but dielectric responses and phonon dynamics typical of liquids. This "crystal-liquid" duality implies that lead halide perovskites belong to phonon glass electron crystals, a class of materials believed to make the most efficient thermoelectrics. We show that the crystal-liqu

This account aims at providing an understanding of singlet fission, i.e., the photophysical process of a singlet state ( S₁) splitting into two triplet states (2 × T₁) in molecular chromophores. Since its discovery 50 years ago, the field of singlet fission has enjoyed rapid expansion in the past 8 years. However, there have been lingering confusion and debates on the nature of the all-important triplet pair intermediate states and the definition of singlet fission rates. H

Thermally activated delayed fluorescence (TADF) molecules are gathering attention for their potential to boost the efficiency of organic light-emitting diodes without precious metals. Minimizing the energy difference between the S₁ and T₁ states (Δ E_ST) is a fundamental strategy to accelerate reverse intersystem crossing (RISC). However, the lack of microscopic understanding of the process prevents adequate design strategies for efficient TADF materials. Here, we

Trivalent europium (Eu³⁺) complexes are attractive materials for luminescence applications if energy transfer from antenna ligands to the lanthanide ion is efficient. However, the microscopic mechanisms of the transfer remain elusive, and fundamental physical chemistry questions still require answers. We track the energy transfer processes in a luminescent complex Eu(hfa)₃(DPPTO)₂ (hfa, hexafluoroacetylacetonate; DPPTO, 2-diphenylphosphoryltriphenylene) using tim

Thermally activated triplet-to-singlet upconversion is attractive from both fundamental science and exciton engineering, but controlling the process from molecular configuration is still unrevealed. In particular, the flexibility of the freedom of molecular geometry is of major importance to understand the kinetics of the phonon-induced upconversion. Here, we focus on two linearly connected donor-acceptor molecules, 9,9-dimethyl-9,10-dihydroacridine-2,4,6-triphenyl-1,3,5-triazine (DMAC-TRZ) and

Lead halide perovskites are promising materials for optoelectronic applications because of their exceptional performances in carrier lifetime and diffusion length; however, the microscopic origins of their unique characteristics remain elusive. The organic-inorganic hybrid perovskites show unique dielectric functions, i.e., ferroelectric-like phonon responses in the 0.1-10 THz region and liquid-like rotational relaxation in the 1-100 GHz range. To reveal the role of the dielectric responses is o

Trivalent lanthanide complexes are attractive light emitters owing to their ideal high color purity. Sensitization using ligands with high absorption efficiency is a powerful approach to enhancing photoluminescence intensity. However, the development of antenna ligands that can be used for sensitization is limited due to difficulties in controlling the coordination structures of lanthanides. When compared to conventional luminescent Eu(iii) complexes, a system composed of triazine-based host mol

Controlling luminescence behaviors of organic chromophores is essential for their applications. As emissions from chromophores are strongly modulated by structural fluctuations and external environments, their comprehensive understandings remain elusive. Here, we demonstrate the modulation of the photophysics of benzophenone (Bzp), a prototypical triplet sensor molecule, by encapsulating it into mesoporous silica nanomaterials (MSNs). We systematically probed photoluminescence property modulatio

While the microscopic transfer properties of carriers are of primary importance for carrier transport of organic semiconductors, the mesoscopic features including the morphologies of grains and the structure of grain boundaries limit the overall carrier transport particularly in polycrystalline organic thin films. Thus the conventional evaluation methods of carrier mobility that rely on macroscopic properties such as $I\text{\ensuremath{-}}V$ curves of devices are not capable to determine carrie

Trivalent europium (Eu(III)) complexes emit narrow-band luminescence as a result of energy transfer following the photoexcitation of antenna ligands. Bidentate β-diketonates are typically used as antenna ligands; however, their entire energy transfer mechanism to Eu(III) remains unknown. We used time-resolved photoluminescence spectroscopy and femtosecond transient absorption spectroscopy to map the complete intramolecular energy transfer process in the [Eu(hfa)₃(TPPO)₂] (h