Optical properties and mechanical induced phase transition of CsPb2Br5 and CsPbBr3 nanocrystals

The Cs-Pb-Br system possesses excellent optical properties and unique phase transition characteristics due to soft lattice structures. Herein, a simple and green synthetic method based on self-assembly in Dimethyl formamide (DMF) is proposed to prepare CsPb2Br5 nanocrystals (NCs) with typical tetragonal structure, which exhibit orange emission and small size around 3.87 nm. Interestingly, the phase transition from CsPb2Br5 to CsPbBr3 occurs easily in DMF through mechanical induction, while the metastable mixed-phase structural CsPbBr3 NCs with an average size of about 5 nm appear and show bright yellow emission. Afterwards, in combination with the supersaturation crystallization method, stable cubic CsPbBr3 NCs with 13 nm size are obtained and display the effective green emission. The synthesized CsPb2Br5 and steady-state CsPbBr3 NCs exhibit good optical stability in solution, while the metastable CsPbBr3 NCs undergo a change in emission from yellow to green with increasing time.