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The microstructure and mechanical properties of polycrystalline spinel ceramics (MgAl2O4) with high translucency were investigated. Several kinds of polycrystalline spinel ceramics were prepared under various sintering conditions, and single-crystal spinel and sapphire were used for comparison. The bending strength of polycrystalline spinel with smaller grain size fabricated without sintering aids exceeded that of single-crystal spinel. The bending strength at 1000°C tended to be lower than that at room temperature. The fracture toughness of polycrystalline spinel prepared without sintering aids measured by SEVNB was higher than that of spinel with sintering aids. By estimation of fracture strength considering different fracture origins, the polycrystalline spinel prepared without sintering aids might be fractured mainly from defects around residual spherical voids. If the size of voids can be minimized in polycrystalline spinel fabricated without sintering aids, both high transmission and good mechanical properties could be achieved. [ABSTRACT FROM AUTHOR]

Two types of transparent Y 2 O 3 ceramics without including large scattering sources such as residual pores, one with very high optical homogeneity (type A) and another one with slightly insufficient optical homogeneity (type B), are purposely prepared, and their optical properties are investigated and compared qualitatively and quantitatively. Type A ceramic exhibits transmittance characteristics with very low internal loss in the visible to infrared wavelength region, while type B ceramic is inferior in various optical performances especially in the short (visible) wavelength region. In type B ceramic, birefringence occurs due to optical inhomogeneity in the visible region, resulting in a decrease in the extinction ratio. Non-uniform refractive index distribution is also observed in the Schlieren image of type B ceramic, hence the laser beam quality through that material is degraded. This study proved the importance of optical homogeneity of transparent ceramics and clarified the problems in actual applications. [ABSTRACT FROM AUTHOR]

Double halide perovskites have outstanding properties for optoelectronic and renewable energy applications. In the present work, we have analszed the structural, mechanical, electronic and optical properties of K2BI6 (B = Ti, Zr and Hf) using the density functional theory. The results show that these perovskites have good mechanical stability. K2HfI6 is a direct bandgap semiconductor with a bandgap of 3.150 eV. K2TiI6 and K2ZrI6 are indirect bandgap semiconductors with bandgaps of 1.828 and 2.515 eV, respectively, but they can be regarded as quasi-direct bandgap semiconductors. They also show good light absorption properties in the ultraviolet–visible wavelength range. These properties make K2BI6 (B = Ti, Zr and Hf) perovskites good candidates for photovoltaic and optoelectronic applications, such as solar cells, photocatalysts and detectors. [ABSTRACT FROM AUTHOR]

The title inorganic-organic hybrid material containing a mixed anion, [BzIQl]2[Zn(NCS)2Br2] (1) (BzIQl = benzyl isoquinolinium, NCS− = isothiocyanate), crystallizes with a benzyl isoquinolinium cation and half of a bis(bromo)-bis(isothiocyanate)zinc(II) anion in the asymmetric unit. It was characterized by elemental analysis, Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-Vis), electrospray ionization mass spectrometry (ESI-MS), and powder and single crystal X-ray diffraction (PXRD and SC-XRD). The organic cation exhibits a Λ-shaped configuration in which two aromatic rings form an inclined dihedral angle of 90.12°. The ZnII ion in the anion is coordinated by two Br ions and two isothiocyanate ions, and two contiguous anions forms a dimer through S···Br interactions. The thermal stability of the hybrid crystal analyzed by thermogravimetric-differential thermal analysis (TG-DTA) reveals that the title crystal was stable up to 170 °C. The PXRD study confirms the phase purity of the crystalline sample. The band gap energy between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) explains the eventual charge transfer interaction that take place mainly between the anion and [BzIQl]+ cation, and the low value (0.46 ev) indicates the suitability of the crystal for optical application. The first hyperpolarizability predicted using density functional theory (DFT) is more than 720 times that of the reference potassium dihydrogen phosphate crystal (KDP). [ABSTRACT FROM AUTHOR]

Biomass burning can significantly impact the chemical and optical properties of carbonaceous aerosols. Here, the biomass burning impacts were studied during wintertime in a megacity of Nanjing, eastern China. The high abundance of biomass burning tracers such as levoglucosan (lev), mannosan (man), galactosan (gal) and non-sea-salt potassium (nss- K+) was found during the studied period with the concentration ranges of 22.4–1476 ng m -3 , 2.1–56.2 ng m -3 , 1.4–32.2 ng m -3 and 0.2–3.8 µ g m -3 , respectively. The significant contribution of biomass burning to water-soluble organic carbon (WSOC; 22.3±9.9 %) and organic carbon (OC; 20.9±9.3 %) was observed in this study. Backward air mass origin analysis, potential emission sensitivity of elemental carbon (EC) and MODIS fire spot information indicated that the elevations of the carbonaceous aerosols were due to the transported biomass-burning aerosols from southeastern China. The characteristic mass ratio maps of lev/man and lev/nss - K+ suggested that the biomass fuels were mainly crop residuals. Furthermore, the strong correlation (p<0.01) between biomass burning tracers (such as lev) and light absorption coefficient (babs) for water-soluble brown carbon (BrC) revealed that biomass burning emissions played a significant role in the light-absorption properties of carbonaceous aerosols. The solar energy absorption due to water-soluble brown carbon and EC was estimated by a calculation based on measured light-absorbing parameters and a simulation based on a radiative transfer model (RRTMG_SW). The solar energy absorption of water-soluble BrC in short wavelengths (300–400 nm) was 0.8±0.4 (0.2–2.3) W m -2 (figures in parentheses represent the variation range of each parameter) from the calculation and 1.2±0.5 (0.3–1.9) W m -2 from the RRTMG_SW model. The absorption capacity of water-soluble BrC accounted for about 20 %–30 % of the total absorption of EC aerosols. The solar energy absorption of water-soluble BrC due to biomass burning was estimated as 0.2±0.1 (0.0–0.9) W m -2 , considering the biomass burning contribution to carbonaceous aerosols. Potential source contribution function model simulations showed that the solar energy absorption induced by water-soluble BrC and EC aerosols was mostly due to the regionally transported carbonaceous aerosols from source regions such as southeastern China. Our results illustrate the importance of the absorbing water-soluble brown carbon aerosols in trapping additional solar energy in the low-level atmosphere, heating the surface and inhibiting the energy from escaping the atmosphere. [ABSTRACT FROM AUTHOR]

Abstract Fabrication of transparent TIG (Tb 3 Fe 5 O 12) ceramics promising for 1.3–1.5 μm optical isolator was successful for the first time by a solid-state reaction between Tb 4 O 7 and Fe 2 O 3. The obtained TIG ceramics was free from grain boundary phases and inclusions but some residual pores were observed in the depth direction. Its in-line transmittance reached ca. 50% in infrared region of 1.1–2.0 μm. Faraday rotation angle of the TIG ceramics was 350deg./cm for 1300 nm, which is about 1.5 times larger than that of the YIG (Y 3 Fe 5 O 12) single crystal. Removal of those residual pores can significantly improve optical properties. Highlights • Succeeded to produce transparent TIG (Tb 3 Fe 5 O 12) ceramics by a simple solid-state reaction of Tb 4 O 7 and Fe 2 O 3 powders. • No wavelength dependency of the in-line transmittance. • Faraday rotation characteristics of the polycrystalline TIG ceramics as same as its single crystal counterpart (350 deg./cm). [ABSTRACT FROM AUTHOR]

Double perovskites A 2 CuSbX 6 (A = Cs, Rb, K; X = Cl, Br, I) have been investigated by first principles calculations. According to the tolerance factor, formation energy, binding energy and elastic stability criterion, the other materials except Cs 2 CuSbI 6 can be judged to have mechanical and thermodynamic stability. All the materials are ductile and show potential in wearable devices. The perovskites possess indirect band structures with bandgaps as 1.163 eV, 0.850 eV, 0.305 eV, 1.140 eV and 1.123 eV for Cs 2 CuSbCl 6 , Cs 2 CuSbBr 6 , Cs 2 CuSbI 6 , Rb 2 CuSbCl 6 and K 2 CuSbCl 6 , respectively. Compared with the other two Cl-based perovskites, K 2 CuSbCl 6 exhibits better optoeletronic properties because of its smaller average effective mass(0.294 m 0 for m h ∗ and 0.201 m 0 for m e ∗), longer carrier lifetime and higher light absorption coefficient (6.58 × 104 cm−1) in visible region. In addition, K 2 CuSbCl 6 has a high Debye temperature which represents better stability. The results indicate that K 2 CuSbCl 6 is an excellent candidate for photovoltaic and optoeletronic devices. [ABSTRACT FROM AUTHOR]

Ultra-high density and optical grade Tb 2 Hf 2 O 7 (THO) pyrochlore ceramics was successfully synthesized by reactive sintering of Tb 4 O 7 and HfO 2 and successive HIP treatment. Residual pores were not observed in the material, and it was optically isotropic in transmission polarization observation. Its optical loss was considerably lower than 0.1%/cm. Optical homogeneity was significantly improved by additional annealing in hydrogen at 1700 °C after the HIP treatment. A very good laser beam profile was observed via the THO ceramics. Verdet constant, insertion loss and extinction ratio of this ceramics at 1064 nm were 50 radT−1m−1, 0.03 dB and 38 dB, respectively, better than that of the commercial TGG single crystal. • Optically homogeneous pyrochlore Tb 2 Hf 2 O 7 (THO) ceramics with low optical loss (0.1%/cm) was successfully produced for Faraday rotator materials by a solid-state reactive sintering and HIP process followed by annealing in hydrogen at high temperature. • Residual pores which cause Mie scattering were not observed in the THO ceramics. • Verdet constant, insertion loss, and extinction ratio of the THO ceramics exceeded the characteristics of commercially available TGG single crystals. [ABSTRACT FROM AUTHOR]

The perovskite materials have been widely used because of their excellent properties. Based on density functional theory, the structural, electronic, elastic, optical and thermodynamic properties of double antiperovskites X 6 BiSbN 2 (X = Mg, Ca, Sr) are calculated. The results show that X 6 BiSbN 2 (X = Mg, Ca, Sr) have stable crystal structures, and their band gaps are 1.172eV, 1.303eV and 0.965eV, respectively. Mg 6 BiSbN 2 is an indirect bandgap semiconductor, which may be more suitable for use as a photocatalyst. Ca 6 BiSbN 2 and Sr 6 BiSbN 2 are direct bandgap semiconductors with high polarization and absorption coefficients, low reflectivity in the visible light region and good mechanical durability, which may be suitable candidates for the absorption layer of perovskite solar cells. In addition, X 6 BiSbN 2 (X = Mg, Ca, Sr) have broad absorption range and high absorption coefficient in the ultraviolet region, which indicates that they may be potential photodetector materials. Sr 6 BiSbN 2 has no entanglement between acoustic and optical branches in the phonon spectrum and a low Debye temperature, which helps to improve the thermoelectric coefficient, so it may be suitable for thermoelectric devices. The calculation results in this paper show that X 6 BiSbN 2 (X = Mg, Ca, Sr) are expected to be used in the absorption layer of solar cells and photodetector field, and Sr 6 BiSbN 2 may also be suitable for thermoelectric devices. • The band gaps of X 6 BiSbN 2 (X = Mg, Ca, Sr) are 1.172eV, 1.303eV and 0.965eV, respectively. • Ca 6 BiSbN 2 and Sr 6 BiSbN 2 may be suitable for the absorption layer of perovskite solar cells. • X 6 BiSbN 2 (X = Mg, Ca, Sr) may be potential photodetector materials. • Sr 6 BiSbN 2 may be suitable for thermoelectric devices. [ABSTRACT FROM AUTHOR]

In this paper, the elastic, optical, electronic and thermodynamic properties and population analysis of double perovskite oxide Ba 2 MgXO 6 (X = Se, Te) are calculated based on first-principles. The results show that the phonon spectrum of Ba 2 MgXO 6 has no virtual frequency, its binding energy and formation enthalpy are negative, which satisfies the Born-Huang stability criterion, indicating that the compound is stable. The elastic parameters of Ba 2 MgXO 6 (X = Se, Te) indicate that they are all brittle materials. Ba 2 MgSeO 6 and Ba 2 MgTeO 6 are direct band gap semiconductor materials with band gap values of 2.197 eV and 2.788 eV, respectively. The charge population analysis indicates that Ba 2 MgXO 6 is a compound with a tendency towards ionic type. The heat capacity reaches the Dulong-Petit limit when the temperature is close to 800K, and both materials show high absorption coefficients in the far ultraviolet spectrum region. Therefore, our study suggests that Ba 2 MgXO 6 (X = Se, Te) may be a good candidate for photovoltaic materials and photoelectric devices in space. [ABSTRACT FROM AUTHOR]

• The band gap values of Rb 2 SeI 6 and K 2 SeI 6 are 1.51 eV and 1.45 eV, respectively, which are very suitable for use as photosensitive materials of solar cells. • The optical parameters indicate that Rb 2 SeI 6 and K 2 SeI 6 have better light absorption characteristics than most lead-free perovskite materials, especially in the visible light range. • The effective mass of electrons and holes of Rb 2 SeI 6 and K 2 SeI 6 are much small than that of many perovskite materials. In this work, we have studied in detail the structural, electronic and optical properties of lead-free double perovskites Rb 2 SeI 6 and K 2 SeI 6 based on first-principles calculations. Their negative binding energy (E b) and formation energy (E f) ensure the stability of the studied materials. Our calculations give band gap values of Rb 2 SeI 6 and K 2 SeI 6 to be 1.51 eV and 1.45 eV, respectively. This illustrates that the two perovskite compounds belong to indirect band gap semiconductors, and are suitable for photosensitive materials of solar cells. For both Rb 2 SeI 6 and K 2 SeI 6 , the valence band maximum (VBM) are dominated by the I-p orbitals, and their conduction band minimum (CBM) are mainly contributed from the I-p orbitals and the Se-p orbitals. The results indicate that the effective mass of electrons and holes in Rb 2 SeI 6 and K 2 SeI 6 is very small, and therefore they are favorable for carrier transport. Moreover, the optical parameters display that Rb 2 SeI 6 and K 2 SeI 6 have significant light absorption properties, especially in the visible light range. Due to the suitable band gap values and excellent light absorption, Rb 2 SeI 6 and K 2 SeI 6 have great application potential in the absorption layer of solar cells. [ABSTRACT FROM AUTHOR]

A novel organic dye with 2D-A structure has been designed and calculated whereby density functional theory (DFT) and time-dependent density functional theory (TD-DFT) for dye-sensitized solar cells. The double-donor branched dye which was consisted of two separated light-harvesting moieties was beneficial to photocurrent generation. First, we discussed the effects of different donor chains on photoelectric performance in the dye molecule, using the DTP-B8 which was a previously reported structure as the reference. Only to conclude that the suitable length can achieve the satisfactory efficiency. Secondly, to modify and sift potential sensitizers further, three series of dyes (BC-series, CB-series and CC-series) were designed and characterized. The increased molar extinction coefficient and the red-shifted λ max was attributed to an increasing in electron conjunction. This work presented a new route to design sensitizers that provide two channels for donating more electrons and improve the final efficiency. It is expected to provide some theoretical guidance on designing and synthetizing high efficiency photosensitive dye in the future experiments. [ABSTRACT FROM AUTHOR]

Water-soluble humic-like substances (HULIS ws) are a group of heterogeneous organic compounds in the atmosphere, greatly impacting climate change and human health. As the most significant biomass burning (BB) and fossil fuel burning polluted area in China, Northeast China Plain could generate more light absorbing HULIS ws to the atmosphere. In this work, daily fine particle (PM 2.5) samples were collected in Changchun, located in Northeast China Plain, from October 17th to November 29th, 2016, to investigate the potential sources of optical properties of HULIS ws. Here, the whole sampling period was divided into three sub-periods using the density of fire spots and the timeline of the central heating: the non-heating (October 17th to October 24th), early heating (October 25th to November 13th), and normal heating (November 14th to November 29th) periods. The mean mass concentrations of HULIS ws were 4.2 ± 1.2, 8.6 ± 3.6, and 2.4 ± 1.3 μg m−3 during the non-heating, early heating, and normal heating periods, respectively. The positive matrix factorization (PMF) model results suggested that the contribution of primary BB, secondary BB, and fossil fuel burning emissions were 46%, 24%, and 19% during the non-heating period, 22%, 29%, and 17% during the early heating period, and 13%, 16%, and 50% during the normal heating period, respectively. Combining the PMF results with the random forest (RF) algorithm, the contribution of each source to the optical properties was quantified. Here, BB still dominated the optical properties of HULIS ws in Northeast China. During the study period, the primary BB and secondary BB contributed 25% and 34% in the light absorption coefficient (Abs), 22% and 33% in the mass absorption exponent (MAE), and 17% and 33% in the absorption Ångström exponent (AAE), respectively. Other sources like cooking and fossil combustion contributed 25% and 35% in Abs, 35% and 26% in MAE, and 16% and 33% in AAE, respectively. • 72% biomass burning emission contributed 40%–50% to light absorption parameters. • 4% cooking emission contributed 16%–35% to light absorption parameters. • This work provides a fast and easy way to quantify the contribution of sources to the light absorption properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • Predicting the basic properties of anti-perovskites X 3 SbP (X = Ca, Sr, Ba) via first-principles. • Theoretical calculation shows that the three materials are stable. • The results show that they are potential solar cell materials, as well as photoelectric materials. In this study, the structure, elastic, electronic and optical properties of anti-perovskites X 3 SbP (X = Ca, Sr, Ba) are theoretically predicted by first-principles. The stability of X 3 SbP is confirmed by the elastic constants, negative formation energy and negative formation enthalpy. From the calculation, we know that Ca 3 SbP, Sr 3 SbP and Ba 3 SbP are direct bandgap semiconductors with bandgap values of 1.52 eV, 1.35 eV and 0.98 eV, respectively. Their energy loss and reflectivity are small in the visible light range, indicating that this kind of materials have small loss and reflected energy of light radiation. In addition, these materials have good light absorption ability in the range of ultraviolet and visible wavelengths. These calculated properties indicate that Ca 3 SbP, Sr 3 SbP and Ba 3 SbP are potential candidates for solar cells, detectors and sensors. [ABSTRACT FROM AUTHOR]

The structural, electronic and optical properties of Cs 2 AgSbX 6 (X = I, Br, Cl) were investigated based on first-principles calculation in this paper. The stability of these materials can be determined by the binding energy, formation energy and two tolerance factors. The results indicate that three materials are indirect band gap, with ideal band gap range of materials for photoelectric applications. The bandgap values of Cs 2 AgSbI 6 , Cs 2 AgSbBr 6 and Cs 2 AgSbCl 6 are 0.84 eV, 1.47 eV and 1.87 eV, respectively. Compared with other perovskites, the effective masses of holes of Cs 2 AgSbX 6 are smaller, which is beneficial to the carrier transport and the performance improvement of optoelectronic devices. Moreover, the exploration of optical characteristics reveal the potential utilization of Cs 2 AgSbX 6 in photovoltaic devices. Based on these calculated results, the double-perovskite Cs 2 AgSbX 6 is a potential candidate for photovoltaic applications. [ABSTRACT FROM AUTHOR]

• Two substituted benzyl triphenylphosphinium picrate salts were synthesized and characterized. • The FT-IR and Raman spectra have been discussed and assigned. • The HOMO-LUMO energy gap explains the charge transfer interactions in the molecules. • The nonlinear optical properties were studies using DFT calculations. • The title crystals exhibit violet and green fluorescence emissions in solid state at room temperature. Two new organic hybrid materials, namely, 4-chlorobenzyl triphenylphosphinium picrate and 4-iodobenzyl triphenylphosphinium picrate [4ClBzTPP][PIC](1) and [4IBzTPP][PIC](2), have been grown by slow evaporation solution growth technique and characterized by elemental analysis, spectroscopy, thermal analysis, powder and single crystal XRD. Two new picrates crystallize in triclinic space group P −1 and consist of a pair of [4ClBzTPP]+/[4IBzTPP]+ cations and picrate anions. The one-dimensional anionic chain are constructed by the non-bonded O···O and N···O interactions. Experimental vibrational bands (IR and Raman) have been discussed and assigned. The HOMO-LUMO energy gap explains the charge transfer interactions in the molecules. TG-TDA technique reveals that two materials were stable up to 215 °C and 253 °C, respectively. Excited by 250 nm ultraviolet light, two materials emit main luminescent emissions bands at about 374 nm and 524 nm in solid state at room temperature. In addition, two picrates show good antibacterial activities against Escherichia coli and Staphylococcus aureus. The results of DFT calculations based on the structures of 1 and 2 indicate that the first hyperpolarizability value (β tot) of two crystals are 5.8 and 32.3 times that of KDP, respectively, which show good nonlinear optical properties. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, the structural, elastic, electronic and optical properties of double-perovskite halides Rb 2 CuBiX 6 are studied using first-principles calculations based on density functional theory. The results show that Rb 2 CuBiX 6 (X = Br, Cl) have thermodynamic and mechanical stability according to the tolerance factor, binding energy, formation energy and Born-Huang stability criterion. The B/G value and Poisson's ratio indicate that Rb 2 CuBiX 6 is a flexible material. Rb 2 CuBiBr 6 and Rb 2 CuBiCl 6 are indirect bandgap semiconductors with bandgap values of 1.11 eV and 1.43 eV, respectively. In addition, the effective masses of electrons of Rb 2 CuBiX 6 are much smaller than that of other perovskite compounds, indicating that they have better carrier mobility. In the visible light range, Rb 2 CuBiX 6 has good dielectric properties and excellent light absorption properties. Therefore, Rb 2 CuBiX 6 has great potential in photovoltaic application due to their suitable bandgap values and excellent optical properties. • The bandgap values of Rb 2 CuBiX 6 (X = Br, Cl) are very suitable for photosensitive materials of solar cells. • The Rb 2 CuBiX 6 can be a potential candidate for excellent light absorbing material. • Rb 2 CuBiX 6 is the structural and thermodynamic stabilities. [ABSTRACT FROM AUTHOR]

The structural, elastic, electronic and optical properties of K 2 CuBiX 6 (X ​= ​Br, Cl) are studied by the first principle calculation in this paper. Their structural and thermodynamic stabilities are guaranteed by the formation energy, binding energy and Born-Huang criterion. The results of elastic constants show that the two materials are ductile and can be applied in foldable optoelectronic devices. Besides, The calculated bandgap values are 1.03 ​eV and 1.44 ​eV for K 2 CuBiBr 6 and K 2 CuBiCl 6 , respectively, which is just in the ideal energy gap range of semiconductors. K 2 CuBiX 6 has very small effective mass advantageous to carrier transport. In addition, the optical properties analysis shows that K 2 CuBiX 6 has excellent light absorption properties in ultraviolet–visible wavelength. Due to their suitable bandgaps and good light absorption, K 2 CuBiX 6 has a promising application in solar cells and other optoelectronic devices. In this study, the perovskites K 2 CuBiX 6 (X ​= ​Br, Cl) are proposed as functional materials in solar cells. [Display omitted] • The K 2 CuBiX 6 (X ​= ​Br, Cl) are very suitable for photosensitive materials of solar cells. • The K 2 CuBiX 6 can be a potential candidate for excellent light absorbing material. • The K 2 CuBiX 6 is the structural and thermodynamic stabilities. [ABSTRACT FROM AUTHOR]

• Cs 2 TlAsX 6 (X = Cl, Br, I) are thermodynamically and mechanically stable. • Cs 2 TlAsX 6 is a functional material with direct bandgap. • Cs 2 TlAsX 6 can be a photoelectric material for its excellent light absorbing. In this work, we have been systematically studied the structural stability, electronic and optical properties of Cs 2 TlAsX 6 (X = I, Br, Cl) by adopting first-principles calculations based on density functional theory (DFT). The mechanical and thermodynamic stability of Cs 2 TlAsX 6 are confirmed by the calculated elastic constants, negative binding energies and formation energies. The calculated Pugh and Poisson's ratio indicate that Cs 2 TlAsI 6 is brittle, and Cs 2 TlAsBr 6 and Cs 2 TlAsCl 6 are ductile. Moreover, the calculated results reveal that Cs 2 TlAsX 6 (X = I, Br, Cl) are direct bandgap semiconductors with values of 1.476 eV, 1.874 eV, and 2.19 eV, respectively. Furthermore, the effective mass of electrons of Cs 2 TlAsX 6 is much smaller than that of many perovskite materials. In addition, all the materials exhibit significant absorption capacity of visible and near ultraviolet light. Perovskite Cs 2 TlAsX 6 is very suitable for solar cell applications and other optoelectronic devices because of its good light absorption performance and narrow band gap. [ABSTRACT FROM AUTHOR]

Recently, more and more vacancy-ordered double perovskites have been proposed as functional materials in optoelectronic devices. In this paper, a simulation work on the structural, electronic and optical properties of vacancy-ordered double perovskites Tl 2 TiX 6 (X ​= ​Cl, Br, I) has been carried out by using first-principles calculations to reveal their potential application in optoelectronic devices. The Goldschmidt's tolerance factors of these compounds are very close to the ideal value of 1 for cubic perovskites, which confirm their structural stability. Moreover, the formation energies of these compounds were also calculated to evaluate their thermodynamic stability. The theoretically predicted lattice constants of Tl 2 TiCl 6 , Tl 2 TiBr 6 and Tl 2 TiI 6 are 10.060 ​Å, 10.553 ​Å and 11.320 ​Å, respectively, which can provide references for future experimental research. The calculated electronic properties indicate that Tl 2 TiCl 6 , Tl 2 TiBr 6 and Tl 2 TiI 6 have direct bandgaps of 3.39 ​eV, 2.57 ​eV and 1.58 ​eV, respectively, showing ideal bandgap nature for optoelectronic applications. Compared with many vacancy-ordered double perovskites, the three Tl 2 TiX 6 compounds all show the advantage of small effective mass of holes. In addition, the investigation of optical properties, such as reflectivity, absorption coefficient and energy loss function in the photon energy range of 0–25 ​eV further confirms the potential utilization of these Tl 2 TiX 6 compounds in optoelectronic devices. In this study, vacancy-ordered double perovskites Tl 2 TiX 6 (X ​= ​Cl, Br, I) are proposed as functional materials in solar cells and other optoelectronic devices. [Display omitted] • The structural and optoelectronic properties of perovskite materials Tl 2 TiX 6 (X = Cl, Br, I) were studied theoretically. • The results show that they are functional materials with direct bandgap nature. • Compared with many vacancy-ordered double perovskites, the effective mass of holes of the studied compounds is very small. • The three Tl 2 TiX 6 compounds are suitable for optoelectronic applications. [ABSTRACT FROM AUTHOR]

In this paper, the structural, elastic, electronic and optical properties of lead-free perovskite derivatives Cs 2 SeX 6 (X = Cl, Br, I) were studied based on first-principles. The results show that the structures of these perovskite derivatives are stable and they are all anisotropic materials. The three perovskite derivatives Cs 2 SeX 6 (X = Cl, Br, I) are all indirect band gap semiconductors, and the band gap values are 3.28 eV, 2.66 eV and 1.69 eV, respectively. Among the three perovskite derivatives, Cs 2 SeI 6 has not only a suitable band gap, but also a smaller carrier mass, a better absorption spectrum and a larger dielectric function in the visible region. Therefore, the perovskite derivative Cs 2 SeI 6 has the best photoelectric properties. Due to the suitable bandgaps and excellent light absorption, the perovskite derivative Cs 2 SeI 6 can be used as potential photoelectric absorption layer materials of solar cells, while Cs 2 SeCl 6 and Cs 2 SeBr 6 have the potential to develop as other optoelectronic devices. • First-principles method was adopted to study the structural, electronic and optical properties of lead-free perovskite derivatives Cs 2 SeX 6 (X = Cl, Br, I). • Because of the suitable value of bandgap and excellent light absorption, the perovskite Cs 2 SeI 6 can be used as potential photoelectric absorption layer materials of solar cells. • The structures of three perovskites Cs 2 SeX 6 (X = Cl, Br, I) are all stable. [ABSTRACT FROM AUTHOR]

In this paper, the structural, electronic and optical properties of vacancy-ordered double perovskites Cs 2 PtI 6 and Rb 2 PtI 6 were studied based on first-principles calculations. The stability of studied compounds is ensured by the negative formation enthalpy. The calculated results show that both Cs 2 PtI 6 and Rb 2 PtI 6 are indirect bandgap semiconductors. The bandgap values of Cs 2 PtI 6 and Rb 2 PtI 6 are 1.29 and 1.15 eV, respectively, which are suitable for photosensitive materials of solar cells. For both Cs 2 PtI 6 and Rb 2 PtI 6 , the valence band maximum (VBM) is dominated by the I-5p orbitals and the conduction band minimum (CBM) is mainly composed of the I-5p orbitals along with the Pt-5d orbitals. The optical properties of Cs 2 PtI 6 and Rb 2 PtI 6 in the photon energy range from 0 to 12 eV have been comprehensively studied by the HSE06 method. The results show that these two compounds exhibit excellent light absorption, especially in the ultraviolet range. Due to the suitable bandgaps and excellent light absorption, the vacancy-ordered double perovskites Cs 2 PtI 6 and Rb 2 PtI 6 can be effective candidates for lead-free photovoltaic materials. • First-principles method was used to study the structural, electronic and optical properties of Cs 2 PtI 6 and Rb 2 PtI 6. • The bandgap values of Cs 2 PtI 6 and Rb 2 PtI 6 are suitable for photosensitive materials of solar cells. • Both Cs 2 PtI 6 and Rb 2 PtI 6 show excellent light absorption in the ultraviolet range. • This work is meaningful for the development of lead-free double perovskites for photovoltaic applications. [ABSTRACT FROM AUTHOR]