Abstract
All-inorganic perovskite CsPbX3 (X=Cl, Br, I) nanostructures such as nanocrystals, nanosheets and nanowires have been increasingly explored in recent years. These CsPbX3 nanostructures have been demonstrated to exhibit excellent optical properties, but their photophysics has not yet clearly understood. In this thesis study, the luminescence mechanisms of CsPbBr3 nanosheets (NSs) are investigated by using various spectroscopic techniques. The main results and findings of this study are summarized as below. Two kinds of excitonic emissions are observed at low temperatures < 80 K under the conditions of low excitation level. Their origins are revealed by examining their spectral features and emission intensity dependence on the excitation power. Thermally induced exchange between the two kinds of excitons is found and modeled quantitatively. The temperature dependence of peak positions and FWHMs are also studied. The role of exciton−phonon coupling in light emission in CsPbBr3 NSs is investigated with a combined PL spectroscopy and the multimode Brownian oscillator (MBO) model in a low temperature range of 5 to 40 K. Several key parameters, including the Huang-Rhys factor characterizing the exciton-longitudinal-optical (LO) phonon coupling strength and the damping constant accounting for the phonon bath (quasi-continuous acoustic phonons) dissipation are examined. PL behavior of CsPbBr3 NSs is investigated in a broad temperature range from 5 to 500 K. The relationship between behavior of PL peak position and phase transition is investigated. The role of phonon scattering, especially at high temperatures, is also studied by examining the PL linewidth. The impact of excitation energy on the luminescence of free and trapped excitons in CsPbBr3 NSs is investigated both experimentally and theoretically. A quantitative model on the basis of the biological population growth theory is developed to interpret the peculiar reduction tendency of PL intensity between the trapped exciton emission and the free exciton emission with increasing the optical excitation energy at 10 K. The different capture coefficient of FX and TX levels is proposed to be responsible for the observed phenomenon. These findings may help to deepen the current understanding of the complex luminescence mechanisms of the perovskite families.
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