Temperature-induced line broadening, line narrowing and line shift in the luminescence of nanocrystalline ZnS:Mn2+

Emission spectra of nanocrystalline ZnS:Mn2+ have been recorded as a function of temperature between 4 and 300 K. For the two emission bands observed (a defect-related emission band around 420 nm and a Mn2+-related emission band around 590 nm), the temperature dependence of the width and the position of the emission bands has been analyzed. The shift and the broadening of the Mn2+ emission can be satisfactorily explained by theoretical models and parameters for electron-phonon coupling that are similar to those for bulk ZnS. For the defect-related emission, the shift to lower energies follows the decrease in bandgap of bulk ZnS with increasing temperature. The width of the defect-related emission decreases as the temperature is raised. This anomalous behavior is explained by inhomogeneous broadening at low temperatures