Understanding the mechanism behind the photochromic properties and light-induced structural and chemical changes in yttrium oxyhydride remains a challenge. This lack of knowledge limits our ability to address degradation, enhance photochromic performance, control color, improve durability, and fully realize the material’s applications. Here, first-principles calculations indicate that anion vacancies may be responsible for the photochromic effect and other key properties of yttrium oxyhydride. These vacancies form deep localized energy levels in the band gap. Sunlight absorption transfers electrons from the valence band to these defect levels, altering the charge state of the vacancies and triggering both the photochromic effect and lattice relaxation. This relaxation involves yttrium cations shifting outward for positively charged vacancies and inward for negatively charged ones, thereby affecting the local environment around the yttrium cations by altering the second coordination shell. Using extended X-ray absorption fine structure spectroscopy on transparent and photo-darkened yttrium oxyhydride films, we show that UV light induces lattice relaxation in the second coordination shell, in agreement with first-principles calculations.

Oxyhydrides of rare-earth metals (REMOHs) exhibit notable photochromic behaviors. Among these, yttrium oxyhydride (YHO) stands out for its impressive transparency and swift UV-responsive color change, positioning it as an optimal material for self-cleaning window applications. Although semiconductor photocatalysis holds potential solutions for critical environmental issues, optimizing the photocatalytic efficacy of photochromic substances has not been adequately addressed. This research advances the study of REMOHs, focusing on the properties of gadolinium oxyhydride (GdHO) both theoretically and experimentally. The electronic and structural characteristics of GdHO, vital for ceramic technology, are thoroughly examined. Explicitly determined work functions for GdH₂, GdHO, and Gd₂O₃ stand at 3.4 eV, 3.0 eV, and 4.3 eV, respectively. Bader charge analysis showcases GdHO’s intricate bonding attributes, whereas its electron localization function majorly presents an ionic nature. The charge neutrality level is situated about 0.33 eV below the top valence band, highlighting these materials’ inclination for acceptor-dominant electrical conductivity. Remarkably, this research unveils GdHO films’ photocatalytic capabilities for the first time. Even with their restricted surface due to thinness, these films follow the Langmuir–Hinshelwood degradation kinetics, ensuring total degradation of methylene blue in a day. It was observed that GdHO’s work function diminishes with reduced deposition pressure, and UV exposure further decreases it by 0.2 eV—a change that reverts post-UV exposure. The persistent stability of GdHO films, hinting at feasible recyclability, enhances their potential efficiency, underlining their viability in practical applications. Overall, this study accentuates GdHO’s pivotal role in electronics and photocatalysis, representing a landmark advancement in the domain.

In recent developments in solar energy research, Sb₂Se₃ and Sb₂S₃ emerge as environment friendly photovoltaic absorber materials, distinguished by their narrow bandgap and high absorption coefficient. Theoretical investigations to determine the electronic structure, effective density of states, dielectric function, and absorption coefficient of Sb₂Se₃ and Sb₂S₃ crystals have been performed using first-principle methods. The results reveal band gap values of about 0.822 and 1.757 eV (PBE method), 1.114 and 1.778 eV (HSE06 method) for Sb₂Se₃ and Sb₂S₃, respectively. The valence band and conduction band edges are primarily formed by Se 4p, S 3p, and Sb 5p hybridized orbitals. The effective density of states (DOS) exhibit magnitudes on the order of 10¹⁹ cm⁻³. Notably, anisotropic characteristics are observed in the real and imaginary parts of the dielectric function. Furthermore, the absorption coefficient surpasses 10⁵ cm⁻¹ at 1 and 1.2 eV for both Sb₂Se₃ and Sb₂S₃. The result indicates that these highly efficient absorber materials are suitable in collecting solar energy.