Crystal field distribution and non-radiative transitions in Cr3+-doped gallogermanates

The large broadening of the fluorescence transitions in Cr3+-doped gallogermanates is attributed to variations in the distortions to the octahedron of nearest-neighbour oxygen ions. For the weak field sites that fluoresce via the 4T2 → 4A2 transition, this causes the Huang-Rhys factor to vary from site to site. Such a crystal field distribution results in strong broadening of the emission band, and also enhances non-radiative decay processes. The non-radiative decay is described in terms of an internal conversion process and modelling shows a confinement potential to reproduce the experimental data most accurately.