Effect of Li⁺ co-doping on structural and luminescence properties of Mn⁴⁺ activated magnesium titanate films

The effect of Li⁺ co-doping on crystal phase formation and photoluminescence (PL) of Mn⁴⁺ activated magnesium titanate films produced by a solid state reaction method at different temperatures (800–1200 °C) has been investigated by using X-ray diffraction (XRD), diffuse reflectance and PL spectroscopy. The chemical composition of sintered films was estimated by energy dispersive X-ray spectroscopy. The concentration of Mn impurity estimated by Electron spin resonance was about 5 × 10¹⁶ cm⁻³. The XRD study of the annealed films revealed several magnesium titanate crystal phases, such as Mg₂TiO₄, MgTiO₃ and MgTi₂O₅. The contribution of each phase depended strongly on the annealing temperature and the presence of Li⁺ additive. Furthermore, Li⁺ co-doping facilitated the formation of both MgTiO₃ and Mg₂TiO₄ phases, especially at lower annealing temperatures. The PL spectra showed two bands centered at 660 and 710 nm and ascribed to the ²E → ⁴A₂ spin-forbidden transition of the Mn⁴⁺ ion in the Mg₂TiO₄ and MgTiO₃, respectively. In Li co-doped films, the integrated intensity of Mn⁴⁺ luminescence was found several times stronger compared to Li-undoped films that was ascribed mainly to flux effect of lithium.