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In this study, we investigated the optoelectronic properties of cubic (Pm3m) and orthorhombic (Pnma) CsPbX3 (X = I, Br, and Cl). We utilized the full potential linear augmented plane wave method, which is implemented in the WIEN2k code, to facilitate the investigation. Different exchange potentials were used to analyze the optoelectronic behavior using the available density functional theory methods. Our findings revealed that CsPbX3 perovskites display direct band gaps at the R and Г points for cubic (Pm3m) and orthorhombic (Pnma) structures, respectively. Among the exchange potentials, the mBJ-GGA method provided the most accurate results. These outcomes concurred with the experimental results. In both Pm3m and Pnma structures, interesting changes were observed when iodide (I) was replaced with bromine (Br) and then chlorine (Cl). The direct band gap at the R and Г points shifted to higher energy levels. Similarly, when I was replaced with Br and Cl, there was a noticeable decrease in the absorption coefficient, dielectric constants, refractive index, and reflectivity, in addition to a band gap shift to higher energy levels. [ABSTRACT FROM AUTHOR]

A new detection technique for photothermal deflection spectroscopy and photoacoustic deflection spectroscopy is presented. The technique uses a pair of matched multiple slits placed in the path of the probe beam and oriented to block the probe light from the detector in the absence of a deflection signal. Significant improvement in the signal-to-noise ratio and in the frequency bandwidth compared with those available with current techniques is demonstrated. OCIS codes: 300.6430, 120.0120.

Abstract: Electronic and optical properties of ternary silver palladium oxide (Ag2PdO2) are investigated using density functional theory. Two different possible approximations for the exchange correlation potentials were employed. The X-ray and neutron crystallographic data were optimized by minimization of the forces (1 mRy/a.u.) acting on the atoms. The electronic structure, electron space charge density, chemical bonding and optical dielectric were determined from the relaxed geometry seeking deep insight understanding of this material. Our calculated energy band gap (0.15 eV) shows a good agreement with the experimental value (0.18 eV). [Copyright &y& Elsevier]

Abstract: The existence of α-Sr2GeN2 and β-Sr2GeN2 were reported recently with their structural properties. In this paper, electronic and optical properties have been investigated using density functional theory. The Perdew–Burke–Ernzerhof generalized gradient approximation (GGA-PBE) is used for the exchange and correlation potential to calculate the optimized parameters of the structures. Our results confirm the previous observation of the atomic positions and lattice parameters for both crystals. The values of the unit cell volume of α- and β-Sr2GeN2 are in good agreement with the experimental values. The local density approximation (LDA), (GGA), the Engel–Vosko GGA approximation (EV-GGA) and the modified Becke–Johnson method (mBJ) were used to calculate the electronic and optical properties. Our results show that α-Sr2GeN2 has a small band gap of about 0.0eV (LDA), 0.050eV (GGA), 0.210eV (EVGGA) and 0.268eV (mBJ) while β-Sr2GeN2 has energy band gap of about 0.10eV (EVGGA) and 0.15eV (mBJ). Additionally, optical dielectric constants were calculated for both ternary compounds. We believe that the current study can provide more information to understand the properties of these ternary nitrides. [Copyright &y& Elsevier]

The effect of halide composition on the structural, electronic, and optical properties of CsPb(Br1−xClx)3 perovskite was investigated in this study. When the chloride (Cl) content of x was increased, the unit cell volume decreased with a linear function. Theoretical X-ray diffraction analyses showed that the peak (at 2θ = 30.4°) shifts to a larger angle (at 2θ = 31.9°) when the average fraction of the incorporated Cl increased. The energy bandgap (Eg) was observed to increase with the increase in Cl concentration. For x = 0.00, 0.25, 0.33, 0.50, 0.66, 0.75, and 1.00, the Eg values calculated using the Perdew–Burke–Ernzerhof potential were between 1.53 and 1.93 eV, while those calculated using the modified Becke−Johnson generalized gradient approximation (mBJ–GGA) potential were between 2.23 and 2.90 eV. The Eg calculated using the mBJ–GGA method best matched the experimental values reported. The effective masses decreased with a concentration increase of Cl to 0.33 and then increased with a further increase in the concentration of Cl. Calculated photoabsorption coefficients show a blue shift of absorption at higher Cl content. The calculations indicate that CsPb(Br1−xClx)3 perovskite could be used in optical and optoelectronic devices by partly replacing bromide with chloride. [ABSTRACT FROM AUTHOR]

We demonstrated the time-resolved dynamics of laser action from the conductive oligomer (CO) 1,4-Bis(9-ethyl-3-carbazo-vinylene)-9,9-dihexyl-fluorene (BECV-DHF). Absorption and fluorescence spectra were studied for BECV-DHF in different solvents under a wide range of concentrations. The Fourier-transform infrared spectroscopy (FTIR) spectrum was measured using simulation and experiments. The Ultraviolet-Visible (UV-VIS) spectra of the BECV-DHF were simulated in two different solutions. This CO formed a dimer and had two vibration bands in nonpolar solvents, partially dissolved in polar protic solvents, and created an H-type aggregate in polar aprotic solvents. BECV-DHF produced amplified spontaneous emission (ASE) at 464 nm in many solvents. The high efficiency of ASE is due to the waveguiding and self-assembly nature of the oligomer, which is very rare for optically pumped systems. However, BECV-DHF did not produce ASE in polar protic solvents. BECV-DHF produced ASE in both longitudinal and transverse pumping, and the full-width half maximum (FWHM) was 4 nm and 8 nm respectively for different solvents, such as toluene and acetone. The CO had a very low threshold pump energy (~0.5 mJ). The ASE efficiency was approximately 20%. The time-resolved spectroscopy (TRS) studies showed a temporal Gaussian-shaped ASE output from this CO. BECV-DHF shows remarkably high stability compare to the conjugated polymer (CP) PFO-co-pX. [ABSTRACT FROM AUTHOR]

A single crystal of the title compound is prepared by the Bridgman-Stockbarger method from the elements and characterized by XRD, absorption coefficient measurements in the energy range of 0.82-1.13 eV, and full potential linear augmented plane wave computations. [ABSTRACT FROM AUTHOR]

Cesium lead bromide (CsPbBr 3 ) perovskite has recently gained significance owing to its rapidly increasing performance when used for light-emitting devices. In this study, we used density functional theory to determine the structural, electronic, and optical properties of the cubic, tetragonal, and orthorhombic temperature-dependent phases of CsPbBr 3 perovskite using the full-potential linear augmented plane wave method. The electronic properties of CsPbBr 3 perovskite have been investigated by evaluating their changes upon exerting spin-orbit coupling (SOC). The following exchange potentials were used: the local density approximation (LDA), Perdew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA), Engel-Vosko GGA (EV-GGA), Perdew-Burke-Ernzerhof GGA revised for solids (PBEsol-GGA), modified Becke-Johnson GGA (mBJ-GGA), new modified Becke-Johnson GGA (nmBJ-GGA), and unmodified Becke-Johnson GGA (umBJ-GGA). Our band structure results indicated that the cubic, tetragonal, and orthorhombic phases have direct energy bandgaps. By including the SOC effect in the calculations, the bandgaps computed with mBJ-GGA and nmBJ-GGA were found to be in good agreement with the experimental results. Additionally, despite the large variations in their lattice constants, the three CsPbBr 3 phases possessed similar optical properties. These results demonstrate a wide temperature range of operation for CsPbBr 3 ., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

Exploring new perovskite-related solid-state materials and the investigating composition-dependent structural and physical properties are highly important for advanced functional material development. Herein, we present the successful hydrothermal synthesis of tetragonal CsPb 2 Cl 5 and the anion-exchange phase formation of CsPb 2 (Cl 1- x Br x ) 5 ( x = 0-1) solid solutions. The CsPb 2 (Cl 1- x Br x ) 5 crystal structures, which crystallize in the tetragonal system, space group I4/ mcm, with parameters similar to those of CsPb 2 Cl 5 , have been determined by Rietveld analysis. The optical band gap was obtained by UV-vis spectroscopy, and the band structure was further calculated by the full-potential method within the generalized gradient approximation. It was revealed that the band gap in CsPb 2 (Cl 1- x Br x ) 5 solid solutions can be tuned over the range of 4.5-3.8 eV by anion substitution.