Extrinsic Photoluminescence and Resonant Raman Spectra of CsPb<sub>2</sub>Br<sub>5</sub> Microspheres
Peng Shen, Xiaoman Ma, Fang Pan, Yanan Wang, Beichen Liu, Honggang Ye
Abstract
Tetragonal CsPb2Br5 has attracted tremendous attention due to its high stability and strong green emission. But its luminescence mechanism has become controversial after it was found to have an indirect band gap of 3.35 eV. Here, the phase structure of a sample is confirmed by its X-ray diffraction pattern and absorption spectrum. The mechanism of the green emission is investigated by its temperature evolution features and the resonant Raman signals. The emission wavelength and its large-scale blue shift with increasing temperature from 10 to 300 K agree well with that of perovskite CsPbBr3, while the theoretical calculation indicates a negligible shift for the optical emission in CsPb2Br5. The photoluminescence intensity, peak width, and temporal decay curves also exhibit a temperature dependence similar to that of CsPbBr3. Additionally, the phonon modes derived from the resonant Raman spectrum of the sample are the same as those found in CsPbBr3 nanocubes. The one at 30 cm–1 is thought to be a specific sign for the existence of CsPbBr3. Therefore, the green emission observed in CsPb2Br5 is proposed to be from the traces of perovskite CsPbBr3.