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Graphical abstract Highlights • Structural transformation for wurtzite BeO under in-plane strain at 16.3%. • Electronic band structure has transformed from direct to indirect when applying large strain. • Electronic and optical properties of unstrained and strained BeO were investigated. • A considerable anisotropy between the components was found for strained BeO. Abstract Structural, electronic, and optical properties of wurtzite BeO under biaxial in-plane strain are investigated using first principles calculations. The present calculations are based on all the electrons' Full-Potential Linearized Augmented Plane Wave plus local orbital (FP-LAPW + lo). The planar strain is introduced to investigate the bonding characteristics, electronic properties, and optical properties of BeO. We observe that BeO is more stable in an h-MgO structure under large tensile strains. Structural, electronic, dielectric, and optical properties of strain-free and strained BeO wurtzite crystal are examined. Our results indicate that the biaxial strains change the bond lengths between Be and O, and we observe a strong correlation between the structural changes accompanying biaxial strains with the electronic structure variations of BeO. The variation in planar strains has a significant impact on the band gap of BeO, which could be proposed as potential candidate for optoelectronic applications. [ABSTRACT FROM AUTHOR]

We have investigated the structural, electronic and optical properties for two phases of polymorphs of hexamethylenetetraminium 2,4-dinitrophenolate monohydrate ( C 6 H 13 N 4 + · C 6 H 3 N 2 O 5 − · H 2 O ) compound which were synthesized by Hoong-Kun Fun's group. The first phase possesess monoclinic P2 1 /m space group, while the other phase has triclinic P1 space group. The all electron full potential linearized augmented plane wave (FP-LAPW + lo) method within the local density approximation (LDA) and the Perdew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA) were used. Calculation shows that the conduction band minimum (CBM) for the two phases is located between D and Z points of the Brillouin zone (BZ) while the valence band maximum (VBM) is located at the center of the BZ, resulting in an indirect band gap. It has been found that the monoclinic (300 K) polymorph possesses a band gap of about 1.884 (LDA) and 1.935 (PBE-GGA) eV while triclinic (143 K) polymorph has a band gap of about 1.720 (LDA) and 1.773 (PBE-GGA) eV. For a deeper insight into the electronic structure, we have performed comprehensive optical properties calculations. These confirm the band gap reduction during the phase transition (300 K→143 K). The bond lengths and angles are calculated and compared with the experimental data; good agreement was found which reveals the accuracy of the calculations. [ABSTRACT FROM AUTHOR]

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]

Highlights: [•] The thin film transistor based on sol–gel processed zinc oxide was fabricated. [•] The ZnO film is formed from the microfibers. [•] The solution-processed ZnO TFT was found to exhibit a high mobility of 0.47cm2/V.s. [Copyright &y& Elsevier]

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: First-principles density functional theory was used to investigate effects of in-plane strains on the structural, electronic, and optical properties of wurtzite cadmium selenide (CdSe). The results of this work show some interesting properties of this material under finite strains that do not exist in the bulk unstrained regime. The structural deformation produced by increasing the in-plane strain, including the internal parameter u, was examined. The result shows that the structure undergoes a phase transition at a strain of 9.3% due to an extraordinary increase of the internal parameter u. By analyzing the electronic band structure using the modified Becke–Johnson approximation (mBJ), a direct–indirect band gap transition at an in-plane strain of 9.3% was found. Additionally, optical dielectric constants, reflectivity, and refractive index were calculated at different values of the strain. These results indicate that, by controlling the CdSe biaxial in-plane lattice constant (for example, by epitaxial growth on an appropriate substrate), the electronic and optical properties can be tuned for specific device applications. [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]

The structural, electronic, and optical features of CsPb(I 1-x Br x) 3 (x = 0, 0.25, 0.50, 0.75, and 1.0) compounds were evaluated using first-principles calculations based on the full-potential linear augmented plane wave (FP-LAPW). The ground-state properties were examined, with a focus on the structural, electronic, and optical properties of the compounds. The structural features were computed using the PBE-GGA potential, revealing that both the lattice constant and bulk modulus varied nonlinearly with respect to the bromide concentration. Theoretical X-ray diffraction analyses revealed peak shifts to larger angles when the average fraction of bromide incorporated increased, indicating shrinkage in the lattice. While the E g values were calculated using the PBE-GGA potential and resulted the 1.45, 1.43, 1.53, 1.50, and 1.77 eV values, the mBJ-GGA potential values resulted the 1.90, 1.81, 2.11, 2.12, and 2.50 eV for CsPbI 3 , CsPbI 2.75 Br 0.25 , CsPbI 1.5 Br 1.5 , CsPbI 0.25 Br 2.75 , and CsPbBr 3 respectively. In addition to that, the E g values of CsPbI 1.5 Br 1.5 which were calculated using other potentials: LDA and PBEsol potentials have resulted the 1.43 and 1.49 eV values, respectively. The E g of CsPb(I 1-x Br x) 3 obtained using mBJ-GGA potential has relatively matched with previously reported experimental values. The calculated effective masses are highly correlated with the energies of E g, the valence-band maximum (VBM), and conduction-band minimum (CBM). We observed that there was an increase, with small bowing parameters (b), in E g value as the Br concentration increases in the CsPb(I 1-x Br x) 3 compounds. The semiconductor characteristic was prominent in the observed band profiles when PBE-GGA and mBJ-GGA potentials were applied. Additionally, the optical properties were examined in details. The calculations indicate that the CsPb(I 1-x Br x) 3 compounds are promising candidates for optoelectronics. Image 1 • The structural, electrical and optical properties of CsPb(I 1-x Br x) 3 were investigated using the PBE-GGA and mBJ-GGA. • An increase in the band gap energy (Eg) values of 0.32 eV (PBE-GGA) and 0.60 eV (mBJ-GGA) when substituting I with Br. • The calculated band gap (Eg) values using the mBJ-GGA were better matched with the experimental values. • The effective masses of electron and hole were calculated using PBE-GGA and mBJ-GGA potentials. • All the optical properties of CsPb(I1-xBrx)3 were investigated using PBE-GGA and mBJ-GGA potentials in details. [ABSTRACT FROM AUTHOR]

In this work, we report on the time resolved spectroscopy of amplified spontaneous emission (ASE) from the conjugated oligomer (CO) 9,10-Bis[(9-ethyl-3-carbazoyl)-vinylenyl]-anthracene (BECVA) only upon energy transfer from another oligomer 1,4-Bis(9-ethyl-3-carbazo-vinylene)-9,9-dihexyl-fluorene (BECV-DHF). BECVA do not dissolve readily in tetrahydrofuran (THF) at room temperature, but completely dissolved when the temperature of the solution (THF & BECVA mix) was risen to 65 °C and remained dissolved even after cooling to room temperature. The process of heating and dissolving do not affect the performance of the CO. The heat-treated solutions were used to perform all experiments, unless mentioned. The absorption spectra indicated no aggregate formation upon increasing concentration, but the fluorescence spectra were very different for several concentrations of the solution, indicating the presence of the excimer. Pure BECVA in THF was pumped at various pump powers and concentrations. This produced only a broadband emission (from 500 to 750 nm) with a FWHM of 250 nm, which has potential applications in white light OLED. Next, we tried to produce ASE using the energy transfer process from a conjugated polymer (CP) poly (9,9-dioctylfluorenyl-2, 7-diyl) (PFO); however, this did not produce ASE, which could be due to the significant hindrance of the macromolecular PFO. The intensity of the BECVA spectra was enhanced with energy transform from PFO. The output was a broadband emission ranging from 400 to 750 nm (FWHM 350 nm). Finally, we added the oligomer BECV-DHF in solution (THF) to the BECVA solution at optimal pump power and concentration of donor (BECV-DHF), and the super-irradiant laser was produced from BECVA at 500 nm with a FWHM of 6 nm. The ultrafast dynamics of the BECVA solution under high pump power excitation and different energy donor (PFO and BECV-DHF) were extensively studied in this work. To the best of our knowledge, this is the first report of a CO that does not intrinsically produce ASE, but produces efficient ASE only via the energy transfer process by another CO. Image 10951 • ASE from the conjugated oligomer (CO) 9,10-Bis[(9-ethyl-3-carbazoyl)-vinylenyl]-anthracene (BECVA). • BECVA does not produce ASE intrinsically for different solvents in wide range of concentration. • ASE could be produce only trough energy transfer from one of the efficient CO BECV-DHF. • The energy transfer process from a macromolecule PFO to BECVA was not efficient. • The TRS studies demonstrated that BECVA begins the emission before the donor (BECV-DHF), even at low concentrations. [ABSTRACT FROM AUTHOR]

This paper is focusing on simulation and analyzing of S-band multi-wavelength Brillouin–Raman fiber laser performance utilizing fiber Bragg grating and Raman amplifier in ring cavity. Raman amplifier-average power model is employed for signal amplification. This laser system is operates in S-band wavelength region due to vast demanding on transmitting the information. Multi-wavelength fiber lasers based on hybrid Brillouin–Raman gain configuration supported by Raman scattering effect have attracted significant research interest due to its ability to produced multi-wavelength signals from a single light source. In multi-wavelength Brillouin–Raman fiber, single mode fiber is utilized as the nonlinear gain medium. From output results, 90% output coupling ratio has ability to provide the maximum average output power of 43 dBm at Brillouin pump power of 20 dBm and Raman pump power of 14 dBm. Furthermore, multi-wavelength Brillouin–Raman fiber laser utilizing fiber Bragg grating and Raman amplifier is capable of generated 7 Brillouin Stokes signals at 1480 nm, 1510 nm and 1530 nm. [ABSTRACT FROM AUTHOR]

• TEM images show that oligomer covers the Perovskite Quantum dot (PQD). • Addition of oligomer enhances PQD's photochemical stability. • Oligomer improves PQD's photo-physical properties. • Oligomer/PQD colloidal blend produces a spectral narrowing under the optical cavity In this paper, we performed steady-state spectroscopy and time-resolved optical spectroscopy (TRS) of conjugated oligomer 1,4-bis(9-ethyl-3-carbazo-vinylene)-9,9-dihexyl-fluorene (BECV-DHF)/perovskite quantum dot (PQD) (C s P b B r 3) (LUMAR)] composites in solution. Furthermore, we investigated the lasing properties of the composites under nanosecond laser pumping. PQDs were dissolved in various solvents. These solutions were blended to form composite solutions with various weight ratios. The transmission, absorption, fluorescence, and band gap of BECV-DHF and PQDs were measured for various solvents and concentrations. Toluene was found to be the best solvent for blending PQDs and BECV-DHF. The absorption and fluorescence spectra of the blends showed the superposition of features of both materials. TEM analysis showed that the BECV-DHF and PQDs were separated by a distance of 9.75 Å. The calculated Förster radius between the BECV-DHF and PQDs was found to be approximately 50 Å – 60 Å. The presence of PQDs in the BECV-DHF solution reduces the lifetime of the excited states of BECV-DHF, and the fluorescence intensity of the PQDs precedes the fluorescence intensity of the BECV-DHF; hence, the underlying mechanism was Förster-type resonant energy transfer (FRET). The spectrally narrow peaks of PQDs and the BECV-DHF/PQDs were obtained at 523 nm using optical cavity. The spectral narrowing of the full width at half maximum (FWHM) was improved from 15 nm to 8.36 nm compared to BECV-DHF/PQDs with pure PQDs. This strategy of obtaining a short-chain stable laser material via the addition of conjugated oligomer could potentially facilitate the development of efficient optoelectronic devices. [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]