Dynamical Investigations of Inhomogeneous Vibrational Broadening in Diluted Magnetic Semiconductor Nanocrystals

Nanocrystalline semiconductors doped with transition metal impurities are appealing candidates for spintronic, photovoltaic, and photocatalytic applications. The electronic nature of these materials is probed experimentally by absorption spectroscopies. Although electronic structure excited state methods are very useful in obtaining insights into the characteristics of excitations, they are generally incapable of reproducing the line shapes observed in experimental spectra. Rigorous line shape analysis was carried out for these systems’ characteristic excitations. The width of corresponding spectral features was found in all cases to result from the inhomogeneous broadening mechanism. A method for simulating finite-temperature, inhomogeneously broadened electronic absorption spectra of large systems with high densities of states is described and applied to the problem of peak broadening in dilute magnetic semiconductor nanocrystals. When applied to Mn2+- and Co2+-doped ZnO nanocrystals, the approach accurately captures the temperature-dependent inhomogeneous broadening of the charge transfer transitions and resolves previous inconsistencies between theory and experiment.