Correlation between inhomogeneous width and crystallite size: 2E → 4A2 luminescence of Co(II) in nanocrystalline ZnAl2O4/Co(II)

We report low-temperature 4A2 ← 2E photoluminescence spectra of nanocrystalline ZnAl2O4/Co(II) as prepared by co-precipitation and subsequent calcination between 600 and 1000 °C. The inhomogeneous width and the peak maximum of the electronic origin are strongly dependent on the particle size, e.g. displaying shifts and widths of −88 and 198 cm−1 for 3 nm crystallites. The lineshape of the electronic origin can be simulated by a ligand field (LF) model that is centred around low-symmetry LF contributions, induced by lattice defects. Transition metal ions can be employed as effective spectroscopic probes for particle size and strain and hence for lattice defect densities in nanocrystallites.