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 CsPb 2 Br 5 nanocrystals (NCs) with typical tetragonal structure, which exhibit orange emission and small size around 3.87 nm. Interestingly, the phase transition from CsPb 2 Br 5 to CsPbBr 3 occurs easily in DMF through mechanical induction, while the metastable mixed-phase structural CsPbBr 3 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 CsPbBr 3 NCs with 13 nm size are obtained and display the effective green emission. The synthesized CsPb 2 Br 5 and steady-state CsPbBr 3 NCs exhibit good optical stability in solution, while the metastable CsPbBr 3 NCs undergo a change in emission from yellow to green with increasing time.