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Heterovalent CsPbBr doping with Bi results in a significant red shift of the optical absorption of both single-crystal and powdered samples. The results of low-temperature (3.6 K) photoluminescence studies of perovskite single crystals indicate that the position of the excitonic luminescence peak remains unaffected by Bi doping that, in turn, infers that the band gap of Bi-doped perovskite is not changed as well. The position and state density distribution of the valence band and Fermi level of single-crystal perovskites were determined by another direct method of ultraviolet photoelectron spectroscopy. The obtained results show that Bi doping causes no changes in the valence band structure but an increase in the Fermi level by 0.6 eV. The summary of the obtained results directly demonstrates that the concept of the band-gap engineering in Bi-doped CsPbBr halide perovskite is not valid.

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The set of Al-doped titania x-Al-TiO 2 (x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.1 wt% Al) has been synthetized by sol-gel method and tested in the reaction of photocatalytic degradation of phenol in aqueous suspension. XRD and Raman studies show that TiO 2 samples have mixedphase rutile-anatase crystalline structure with linear increase of anatase fraction from 0.0 wt% for 0.0-Al-TiO 2 up to 18 wt% for 1.1-Al-TiO 2 . The decrease of the particle size from ∼ 800 nm to 50 nm and the increase of specific surface area from 1.7 m 2 /g up to 28 m 2 /g with increased content of Al have been observed. The data of XRD, XPS, Raman spectroscopy and EDS

We present optical study of MAPbBr 3 single crystals grown from solution by inverse temperature crystallization method. Photoluminescence temperature dependence of narrow and isolated exciton resonance showed encouragingly low inhomogeneous broadening Γ ≈ 0.5 meV, which is comparable to those of MBE-grown III-V heterostructures, indicating high quality of the solution-grown perovskite. Excitonic origin of the resonance was proved by its superlinear pump intensity dependence in contrast to the linear behavior of the defect-assisted recombination bands. In addition, for the first time phonon replicas were resolved in MAPbBr 3 photoluminescence spectra and attributed to the known lattice vibrational modes by comparison with Raman scattering spectra.