Structural phase stability, electronic structure, optical properties, and high-pressure behavior of polytypes of In 2 O 3 in three space group symmetry I2 1 3, Ia3 and R3 are studied by first-principles density functional calculations. From structural optimization studies lattice and positional parameters have been calculated, which are found to be in good agreement with the corresponding experimental data. In 2 O 3 of space group symmetry I2 1 3 and Ia3 are shown to undergo a pressureinduced phase transition to IO3 at pressures around 3.83 GPa. From analysis of band structure it is found that In 2 O 3 of space group symmetry I2 1 3 is indirect band gap semiconductors, while the other phase of space group Ia3 is direct band gap. The calculated carrier effective masses for all these three phases are compared with available experimental and theoretical values. From chargedensity and electron localization function analysis it is found that these phases have dominant ionic bonding. The magnitude of the absorption and reflection coefficients of In 2 O 3 with space group Ia3 and R3 are small in the energy range 0-5 eV, so that these materials can re regarded and classified as transparent.

Abstract:In this work we report on photochromism in transparent thin film samples of oxygencontaining yttrium hydride. Exposure to visible and ultraviolet (UV) light at moderate intensity triggers a decrease in the optical transmission of visible and infrared (IR) light. The photo-darkening is colour-neutral. We show that the optical transmission of samples of 500 nm thickness can be reduced by up to 50% after one hour of illumination with light of moderate intensity. The reaction is reversible and samples that are left in the dark return to the initial transparent state. The relaxation time in the dark depends on the temperature of the sample and the duration of the light exposure. The photochromic reaction takes place under ambient conditions in the as-deposited state of the thin-film samples. Graphical abstract:Research highlights:-Photochromic response in the as-deposited state at ambient conditions -Sensitive to visible and ultraviolet light -Color-neutral photo-darkening -Persistent photoconductivity accompanies the photochromic darkening -Reversible reaction, material relaxes back to transparent state when left in dark

Electronic structure and band characteristics for zinc monochalcogenides with zinc-blende-and wurtzite-type structures are studied by first-principles density-functional-theory calculations with different approximations. It is shown that the local-density approximation underestimates the band gap and energy splitting between the states at the top of the valence band, misplaces the energy levels of the Zn-3d states, and overestimates the crystal-field-splitting energy. The spin-orbit-coupling energy is found to be overestimated for both variants of ZnO, underestimated for ZnS with wurtzitetype structure, and more or less correct for ZnSe and ZnTe with zinc-blende-type structure. The order of the states at the top of the valence band is found to be anomalous for both variants of ZnO, but is normal for the other zinc monochalcogenides considered. It is shown that the Zn-3d electrons and their interference with the O-2p electrons are responsible for the anomalous order. The effective masses of the electrons at the conduction-band minimum and of the holes at the valence-band maximum have been calculated and show that the holes are much heavier than the conduction-band electrons in agreement with experimental findings. The calculations, moreover, indicate that the effective masses of the holes are much more anisotropic than the electrons. The typical errors in the calculated band gaps and related parameters for ZnO originate from strong Coulomb correlations, which are found to be highly significant for this compound. The local-density-approximation with multiorbital mean-field Hubbard potential approach is found to correct the strong correlation of the Zn-3d electrons, and thus to improve the agreement between the experimentally established location of the Zn-3d levels and that derived from pure LDA calculations.

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Electronic band structure and optical properties of zinc monochalcogenides with zinc-blende-and wurtzite-type structures were studied using the ab initio density functional method within the LDA, GGA, and LDA+U approaches. Calculations of the optical spectra have been performed for the energy range 0-20 eV, with and without including spin-orbit coupling. Reflectivity, absorption and extinction coefficients, and refractive index have been computed from the imaginary part of the dielectric function using the Kramers-Kronig transformations. A rigid shift of the calculated optical spectra is found to provide a good first approximation to reproduce experimental observations for almost all the zinc monochalcogenide phases considered. By inspection of the calculated and experimentally determined band-gap values for the zinc monochalcogenide series, the band gap of ZnO with zinc-blende structure has been estimated.

Oxygen-containing yttrium hydride thin films exhibit photochromic behavior: Transparent thin films reversibly switch from a transparent state to a photodarkened state after being illuminated with UV or blue light. From optical spectrophotometry and ellipsometry measurements of the transparent state and photodarkened state, it is concluded that the photochromic effect can be explained by the gradual growth, under illumination, of metallic domains within the initial wide-band-gap semiconducting lattice. This conclusion is supported by Raman measurements. DOI: 10.1103/PhysRevB.95.201301 Oxygen-containing yttrium hydride films exhibit photochromic (PC) behavior, i.e., the optical properties of the films change reversibly when illuminated by light of adequate energy (wavelengths in the blue or UV range). Early works by Hoekstra et al. [1] reported photoconductivity in yttrium hydrides at low temperature, and Ohmura et al. [2,3] accidentally discovered PC behavior in yttrium hydride films subjected to high pressure. In addition, Huiberts et al. observed for the first time the gasochromic behavior of yttrium hydride thin films [4]. Later, Mongstad et al. [5,6] reported PC behavior in transparent oxygen-rich yttrium hydride films under atmospheric conditions and at room temperature. In the latter case, however, the yttrium hydride films were directly obtained by reactive magnetron sputtering rather than by the subsequent hydrogenation of a predeposited metallic Y layer. Oxygen-rich yttrium hydride is not the only oxygen-containing hydride which exhibits interesting physical properties. For instance, Miniotas et al. have reported gigantic resistivity and band-gap changes in oxygen-containing gadolinium hydride [7].The mechanism of the PC behavior in oxygen-rich yttrium hydride is still unclear and seems to have no relation to the PC mechanism reported for transition-metal oxides [8]. In the present Rapid Communication, the properties of oxygen-rich transparent semiconducting yttrium hydride thin films-hereafter referred to as YH x O sc w , where the superscript sc refers to their semiconducting character-and of opaque metallic yttrium hydride thin films-from now on referred to as YH y O m z , where y < x and where the superscript m refers to their metallic character-have been investigated by grazing incidence x-ray diffraction (GIXRD), Raman spectroscopy, ellipsometry, and spectrophotometry. Both sets of films, YH x O sc w and YH y O m z , were deposited onto soda-lime glass substrates by sputter deposition at a hydrogen/argon ratio = 0.18 and 0.13, respectively, and then exposed to air where they oxidize. A detailed description of the deposition method can be found in our previous work [9] Chandran et al. [8], which reports changes of the hydrogen species in oxygen-containing yttrium hydride after illumination, suggesting the release of electrons and the formation of a metallic phase.Figure 1(a) shows GIXRD patterns-obtained by using Cu Kα radiation at a fixed angle of incidence of 2• in a Bruker Siemens D5000 diffr...

It has been recently demonstrated that yttrium oxyhydride (YHO) films can exhibit reversible photochromic properties when exposed to illumination at ambient conditions. This switchable optical property enables their utilization in many technological applications, such as smart windows, sensors, goggles, medical devices, etc. However, how the composition of the films affects their optical properties is not fully clear and therefore demands a straightforward investigation. In this work, the composition of YHO films manufactured by reactive magnetron sputtering under different conditions is deduced in a ternary diagram from Timeof-Flight Elastic Recoil Detection Analysis (ToF-ERDA). The results suggest that stable compounds are formed with a specific chemical formula-YH 2-δ O δ. In addition, optical and electrical properties of the films are investigated, and a correlation with their compositions is established. The corresponding photochromic response is found in a specific oxygen concentration range (0.45 < δ < 1.5) with maximum and minimum of magnitude on the lower and higher border, respectively.

Thin films of oxygen-containing yttrium hydride show photochromic effect at room temperature. In this work, we have studied structural and optical properties of the films deposited at different deposition pressures, discovering the possibility of engineering the optical band gap by variation of the oxygen content. In sum, the transparency of the films and the wavelength range of photons triggering the photochromic effect can be controlled by variation of the deposition pressure.