Over the past decade, hybrid metal–halide perovskites have garnered significant interest for optoelectronic and photonic applications due to their exceptional light-emission properties—such as high photoluminescence quantum yield, optical gain, and amplified spontaneous emission—making them promising materials for LEDs, light-emitting transistors, and lasers.

Despite extensive studies, the fundamental photophysical mechanisms underlying ASE in these materials remain incompletely understood.

In this work, we conduct a detailed investigation of the temperature-dependent behavior of ASE and photoluminescence (PL) in a MAPbBr₃ thin film over the temperature range of 20–300 K, under both nanosecond-pulsed and continuous-wave (cw) excitation.

Under nanosecond excitation, ASE is observed throughout the entire temperature range, with a threshold that exhibits a marked temperature dependence. This behavior is attributed to thermally activated non-radiative processes. Discontinuities in the ASE threshold are observed at approximately 90 K and 190 K, corresponding to the orthorhombic–tetragonal and tetragonal–cubic phase transitions, respectively, leading to different activation energies and coupling rates of the non-radiative process.

Spontaneous emission, under both pulsed and cw excitation, reveals the contributions of free excitons (FE), bound excitons (BE), and trap states —only evident below 100 K — with their relative intensities depending on temperature and excitation conditions.

By comparing emission behavior across both excitation regimes and the temperature range, we find that ASE predominantly originates from BE, and among the three structural phases, the orthorhombic phase displays the most favorable ASE characteristics, with the lowest threshold and the weakest temperature dependence.

Our results shed light on the fundamental optical processes in MAPbBr₃ thin films, emphasizing the key role of the crystalline phase in ASE performance and the contribution of trap-related emissions to PL. These insights are crucial for guiding further improvements in the emission properties of hybrid lead halide perovskites, which are used in advanced photonic and optoelectronic applications.