Role of Localized States in Photoluminescence Dynamics of High Optical Gain CsPbBr₃ Nanocrystals

Abstract Temperature‐dependent time‐resolved photoluminescence (TRPL) spectroscopy of high optical gain CsPbBr₃ nanocrystals (NCs) films along with temperature‐dependent steady‐state absorption and photoluminescence (PL) spectra is studied. A red shift in the optical band edge and the corresponding PL peak is observed by lowering the temperature from room temperature, analogous to hybrid perovskite semiconductors. However, the faster PL decay of CsPbBr₃ NCs film at a low temperature as compared to room temperature is in contrast with many other traditional colloidal quantum dots. The TRPL spectroscopy as a function of temperature suggests the presence of a red‐shifted (≈75 ± 15 meV) defect‐induced emission peak at longer times. Temperature‐dependent PL intensity study shows an Arrhenius type of character with two activation energies: ≈77 ± 18 and ≈12 ± 3 meV. A qualitative model is developed where interaction between the excitonic level and these observed localized states as a function of temperature can qualitatively explain the contrasting PL decay mechanism of CsPbBr₃ NCs film. To ensure the quality of in‐house synthesized CsPbBr₃ NCs with a mixture of oleylamine and octylamine ligands, the amplified spontaneous emission from CsPbBr₃ NCs film as a planar waveguide medium is studied, which shows state‐of‐art optical gain coefficient of ≈51cm⁻¹ and a loss coefficient of ≈15cm⁻¹ at room temperature.