Figure 26.

(a) An approximate band diagram of a CsPbX₃ perovskite without (left) and with (right) inclusion of effects of spin–orbit coupling (SOC). If one accounts for splitting of the CB states due to SOC, the CB band-edge degeneracy is reduced from 4 to 2. (b) The early- and late-time PL signals (A and B, respectively) of the CsPbBr_1.5I_1.5 nanocrystals as a function of ⟨N⟩ obtained from the PL time transients (inset) recorded using excitation with 3.6 eV, 220 fs pulses. At large ⟨N⟩, when both signals are saturated, their ratio is controlled by the degeneracies of the CB and VB states that define their maximal occupancies. Based on the conducted modeling, the measurements are best described assuming g_e = g_h = 2 (black solid line). The dashed lines show modeling for g_min = 2 and g_max = 4 (blue), and g_min = g_max = 4 (green). Here, g_min = min(g_e, g_h) and g_max = max(g_e, g_h). The red line is calculated from (1 – p₀), there p₀ is the fraction of unexcited nanocrystals obtained using Poisson statistics of photon absorption events. Adapted with permission from ref (100). Copyright 2016 American Chemical Society.