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The parameters of monoclinic unit cell of TlInSeS layered crystals were determined from X-ray powder diffraction study. The optical properties of TlInSeS have been investigated by means of transmission and reflection measurements in the wavelength range of 500–1100 nm. The optical indirect transitions with band gap energy of 2.05 eV and direct transitions with band gap energy of 2.21 eV were found by means of the analysis of the absorption data at room temperature. Transmission measurements carried out in the temperature range of 10–300 K revealed that the rate of change of the indirect band gap with temperature is γ = -4.7 × 10^-4 eV/K. The dispersion of the refractive index is discussed in terms of the single oscillator model. The refractive index dispersion parameters: oscillator wavelength and strength were found to be 2.78 × 10^-7 m and 1.21 × 10¹⁴m^-2, respectively.

In this paper, glass sample was prepared by the conventional wet chemical method. A series of borate glass consists of lithium and potassium carbonate doped with 0.1mol% of NH₄ H₂PO₄ and copper oxides have been well prepared. The structural and the optical properties of the glass have been measured by means of their XRD, FTIR, PL and UV-VIS spectra. From the results, the current sample shows a nonlinear optical property by emitting two prominent peaks at 504 and 540 nm (green light emission) under the excitation of 630 nm. A significant enhancement on the PL spectra due to increment of phosphorus impurities dopant has also been observed. Some other physical parameters were also been measured and identified. The results of structural as well as the optical were then being estimated and discussed.

The bulk energy gap of two-dimensional (2D) topological insulators (TIs) is generally small, leading to their study being limited to extremely low temperatures, thus increasing the energy gap of 2D TIs is an urgent challenge. It has been reported that the compressive strain could enhance the band gap of the 2D TI to about 55 meV. Based on this result, this paper further calculated the band structures of 2D TIs with a special structure, i.e., the double quantum well, and especially evaluated their band gaps. We found that by choosing different internal barrier thicknesses, asymmetry factors and electric fields, numerical results show that the energy gap of the TIs with double quantum well (DQW) structure can further reach over 70 meV. This result might be significant for the possible applications of 2D TIs.

CuO:Cu₂O/Si heterojunctions have been prepared with different concentrations of Cu₂O nanoparticles using the thermal evaporation technique. The X-ray diffraction (XRD) results show that the prepared films are polycrystalline with orthorhombic structure and preferential orientation (110) direction along the $c$ axis at $2𝜃=32.82^{\circ }$, which corresponds to the pure CuO with crystallite size 18nm, while the particle size ranged from 14nm to 34 nm (resulted from SEM test). The optical properties were studied by recording the absorbance spectra using the UV–visible spectrophotometer. The absorbance increased with Cu₂O doping. The high values of the energy gap refer to the quantization effect. The electrical properties including the Hall effect were studied. CuO:Cu₂O/Si heterojunctions have been prepared at different concentrations. $I$–$V$ characteristics show that the Cu₂O doping increases the energy conversion efficiency by retarding the electron–hole recombination and the improved device performance is caused by the high short-circuit current ($I_{\mathrm{\text{sc}}})$ and open circuit voltage ($V_{\mathrm{\text{oc}}})$ and found that the highest efficiency ($\eta )$ at doping 0.006 Cu₂O 3.471% with $V_{\mathrm{\text{oc}}}$ of 2.20V, $I_{\mathrm{\text{sc}}}$ of 0.0170mA cm${}^{-2}$ and F.F of 0.6497 at $P=100$mW/cm².

Quaternary glasses were successfully fabricated using melt quenching technique based on the chemical compound composition ($x$)Bi₂O₃–($0.5-x$) ZnO–(0.2)B₂O₃–(0.3)SiO₂, where ($x=0.1$, 0.2, 0.3, 0.4, 0.45) mole. The sources of SiO₂ was produced from rice husk ash (RHA) at 99.36% of SiO₂. The Urbach energy was increased from 0.16eV to the 0.29eV as the mole of Bi₂O₃ increased in the glass structure. The indirect energy band gap is indicated in decrement pattern with 3.15eV towards 2.51eV. The results of Urbach energy and band gap energy that were obtained are due to the increment of Bi${}^{3+}$ ion in the glass network. The refractive indexes for the prepared glasses were evaluated at 2.36 to 2.54 based on the Lorentz–Lorentz formulation which correlated to the energy band gap. The calculated of molar polarizability, electronic polarizability and optical basicity exemplify fine complement to the Bi₂O₃ addition in the glass network. The glass sample was indicated in amorphous state.