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Study of the local optical properties using electron beam (e-beam) can provide a valuable information concerning the inspection of the materials quality, the presence of the different phase inclusions and defects. Halide perovskites have been shown to be highly sensitive to external stress conditions like ambient atmosphere, light, and heat. In this paper, the cathodoluminescence (CL) spectroscopy has been exploited to carry out the investigation of CH3NH3PbBr3 monocrystals under low energy electron beam irradiation. The CL spectra exhibited strong transformation with the increase of the irradiation dose and significant shifts of the peak maximums from 2.23 eV to >2.5 eV. Utilizing a larger e-beam energy (>20 keV) was found to be preferable to slow down the dynamics of the decomposition and corrosion. The mechanisms of the changes in MAPbBr3 properties after e-beam exposure and correlation to the in-depth distribution of deposited energy were discussed., Comment: 8 pages, 3 figures

During the last years, giant optical anisotropy demonstrated its paramount importance for light manipulation which resulted in numerous applications ranging from subdiffraction light guiding to switchable nanolasers. In spite of recent advances in the field, achieving continuous tunability of optical anisotropy remains an outstanding challenge. Here, we present a solution to the problem through chemical alteration of the ratio of halogen atoms (X = Br or Cl) in single-crystal CsPbX$_3$ halide perovskites. It turns out that the anisotropy originates from an excitonic resonance in the perovskite, which spectral position and strength are determined by the halogens composition. As a result, we manage to continually modify the optical anisotropy by 0.14. We also discover that the halide perovskite can demonstrate optical anisotropy up to 0.6 in the visible range -- the largest value among non-van der Waals materials. Moreover, our results reveal that this anisotropy could be in-plane and out-of-plane, depending on perovskite shape -- rectangular and square. Hence, it can serve as an additional degree of freedom for anisotropy manipulation. As a practical demonstration, we created perovskite anisotropic nanowaveguides and show a significant impact of anisotropy on high-order guiding modes. These findings pave the way for halide perovskites as a next-generation platform for tunable anisotropic photonics., Comment: 18 pages, 3 figures