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.