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1. Transport and optical properties of the chiral semiconductor Ag ₃ AuSe ₂

   https://doi.org/10.1002/zaac.202200055  

   Won, Juyeon; Kim, Soyeun; Gutierrez‐Amigo, Martin; Bettler, Simon; Lee, Bumjoo; Son, Jaeseok; Won Noh, Tae; Errea, Ion; Vergniory, Maia G.; Abbamonte, Peter; et al (May 2022, Zeitschrift für anorganische und allgemeine Chemie)

   Abstract Previous band structure calculations predicted Ag₃AuSe₂to be a semiconductor with a band gap of approximately 1 eV. Here, we report single crystal growth of Ag₃AuSe₂and its transport and optical properties. Single crystals of Ag₃AuSe₂were synthesized by slow‐cooling from the melt, and grain sizes were confirmed to be greater than 2 mm using electron backscatter diffraction. Optical and transport measurements reveal that Ag₃AuSe₂is a highly resistive semiconductor with a band gap and activation energy around 0.3 eV. Our first‐principles calculations show that the experimentally determined band gap lies between the predicted band gaps from GGA and hybrid functionals. We predict band inversion to be possible by applying tensile strain. The sensitivity of the gap to Ag/Au ordering, chemical substitution, and heat treatment merit further investigation. 

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2. Temperature-dependent optical properties of monocrystalline CaF ₂ , BaF ₂ , and MgF ₂

   https://doi.org/10.1364/OME.496246  

   Zheng, Qifan; Wang, Xinchao; Thompson, Dakotah (July 2023, Optical Materials Express)

   CaF₂, BaF₂, and MgF₂are low-index, infrared-transparent materials that are extensively used in optical systems. Despite their technological importance, a systematic investigation into the temperature dependence of their optical properties is lacking. In this study, spectroscopic ellipsometry was used to obtain the refractive index of monocrystalline CaF₂, BaF₂, and MgF₂for wavelengths between 220 nm and 1700 nm, and for temperatures between 21 °C and 368 °C. The raw ellipsometric data was fit to a Sellmeier model with temperature-dependent oscillator terms to extract the real part of the refractive index of each material. The refractive index of CaF₂and BaF₂was observed to decrease linearly with increasing temperature, which can be largely attributed to a reduction in the mass density due to thermal expansion. In contrast, the refractive index of MgF₂was found to vary nonlinearly with temperature, which suggests competing effects from the material’s electronic polarizability. The temperature-dependent refractive index data reported here provide a finely-resolved mapping of the thermo-optic coefficient for these three materials, which could inform the development of optical devices operating at elevated or unsteady temperatures. 

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3. Optical Properties and Photocarrier Dynamics of Bi ₂ O ₂ Se Monolayer and Nanoplates

   https://doi.org/10.1002/adom.201901567  

   Liu, Shuangyan; Tan, Congwei; He, Dawei; Wang, Yongsheng; Peng, Hailin; Zhao, Hui (January 2020, Advanced Optical Materials)

   Abstract A comprehensive experimental study on optical properties and photocarrier dynamics in Bi₂O₂Se monolayers and nanoplates is presented. Large and uniform Bi₂O₂Se nanoplates with various thicknesses down to the monolayer limit are fabricated. In nanoplates, a direct optical transition near 720 nm is identified by optical transmission, photoluminescence, and transient absorption spectroscopic measurements and is attributed to the transition between the valence and conduction bands in the Γ valley. Time‐resolved differential reflection measurements reveal ultrafast carrier thermalization and energy relaxation processes and a photocarrier recombination lifetime of about 200 ps in nanoplates. Furthermore, by spatially resolving the differential reflection signal, a photocarrier diffusion coefficient of about 4.8 cm²s⁻¹is obtained, corresponding to a mobility of about 180 cm²V⁻¹s⁻¹. A similar direct transition is also observed in monolayer Bi₂O₂Se, suggesting that the states in the Γ valley do not change significantly with the thickness. The temporal dynamics of the excitons in the monolayer is quite different from the nanoplates, with a strong saturation effect and fast exciton–exciton annihilation at high densities. Spatially and temporally resolved measurements yield an exciton diffusion coefficient of about 20 cm²s⁻¹. 

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4. Thermo-Optical Modulator Based on VO ₂ and Graphene Plasmonics

   https://doi.org/10.1109/JPHOT.2025.3581488  

   Vatani, Sareh; Faramarzi, Vahid; Park, Jeongwon (August 2025, IEEE Photonics Journal)
5. Inorganic Molecular Electride Mg ₄ O ₃ : Structure, Bonding, and Nonlinear Optical Properties

   https://doi.org/10.1002/chem.201806372  

   Kulichenko, Maksim; Fedik, Nikita; Bozhenko, Konstatin V.; Boldyrev, Alexander I. (March 2019, Chemistry – A European Journal)