Influence of Al3+doping on the energy levels and thermal property of the 3.5MgO·0.5MgF2·GeO2:Mn4+ red-emitting phosphor*

A series of Al3+ -doped 3.5MgO0.5MgF2GeO2:Mn4+ red-emitting phosphors is synthesized by high temperature solid-state reaction. The broad excitation band at 300 nm–380 nm, resulting from the 4A2 → 4T1 transition of Mn4+, exhibits a blue shift with the increase of Al2O3 content. The observation of the decreased Mn4+O2 − distance is explained by the crystal field theory. The temperature-dependent photoluminescence spectra with various amounts of Al2O3 content are comparatively measured and the calculation shows that the activation energy increases up to 0.41 eV at the Al2O3 content of 0.1 mol. The maximum phonon densities of state for these samples are calculated from Raman spectra and they are correlated with the thermal properties.