Tantalum oxynitride has been studied as an active photocatalyst under visible light, using a full potential linearized augmented plane wave method within the framework of density functional theory. The electronic and optical properties of TaON are calculated using local density approximation (LDA), generalized gradient approximation (GGA), Engel–Vosko generalized gradient approximation (EVGGA) and the modified Becke–Johnson (mBJ) potential approximation to describe the exchange–correlation potential. The calculated band gap value obtained by the mBJ approximation approach (2.5 eV) is very close to the experimental result (2.5 eV). We found that hybridization among the Ta-d, O-p and N-p states results in the formation of a covalent bond between Ta–N and Ta–O. The calculated optical properties confirm that the TaON is an active photocatalyst under visible light irradiation. TaON has a high dielectric constant and the components show anisotropy in the energy range between 3.0 eV and 10.0 eV. A high refractive index of 2.47 at 632.8 nm is obtained which shows better agreement with the experimental value (2.5 at 632.8 nm) than previous results.

Photoelectrical properties of Tl_1−xIn_1−xSn_xSe₂ single crystalline alloys (x = 0, 0.1, 0.2, 0.25) grown using the Bridgman–Stockbarger method were studied. The temperature dependence of electrical and photoconductivity for the Tl_1−xIn_1−xSn_xSe₂ single crystals was explored. It has been established that photosensitivity of the Tl_1−xIn_1−xSn_xSe₂ single crystals increases with x. The spectral distribution of photocurrent in the wavelength spectral range 400–1000 nm has been investigated at various temperatures. Photoconductivity increases in all the studied crystals with temperature. Therefore, thermal activation of photoconductivity is caused by re-charging of the photoactive centers as the samples are heated. Based on our investigations, a model of center re-charging is proposed that explains the observed phenomena. X-ray photoelectron valence-band spectra for pristine and Ar⁺-ion irradiated surfaces of the Tl_1−xIn_1−xSn_xSe₂ single crystals have been measured. These results reveal that the Tl_1−xIn_1−xSn_xSe₂ single-crystal surface is sensitive to the Ar⁺ ion irradiation that induced structural modification in the top surface layers. Comparison on a common energy scale of the X-ray emission Se Kβ₂ bands representing energy distribution of the Se 4p-like states and the X-ray photoelectron valence-band spectra was done.