Optical and Structural Properties of Mn⁴⁺-Activated (Zn_xMg_1–x)₂TiO₄ Red Phosphors

A report on optical and structural investigations of Mn⁴⁺-activated (Zn_xMg_1–x)₂TiO₄ red phosphors by X-ray diffraction, photoluminescence (PL), and electron paramagnetic resonance methods is provided. The phosphors of Mg₂TiO₄, Zn₂TiO₄ and solid solutions (Zn_xMg_1–x)₂TiO₄ (x = 0.25, 0.50, 0.75) with manganese content of 0.1 mol% are synthesized at temperatures in the range of 800–1200 °C via solid state reaction. Formation of solid solutions of inverse spinel structure demonstrates the features similar to both the Mg₂TiO₄ and Zn₂TiO₄, i.e., decomposition of the (Zn,Mg)₂TiO₄ on the (Zn,Mg)TiO₃ and MgO and separation of the secondary ZnO phase, respectively. These processes depend on the composition of solid solution and sintering temperature, and for some regimes, the single-phase phosphor can be obtained. The largest intensity of Mn⁴⁺ red PL is found in the Mn-doped (Zn_0.25Mg_0.75)₂TiO₄ phosphor sintered at 1100 °C and it is 2 times larger than those in similar Mn⁴⁺-activated Mg₂TiO₄ phosphor. The differences in the PL intensity of the phosphors of solid solutions are explained by different PL thermal quenching as well as by competing processes of Mn incorporation in +2 and +4 charge states in zinc–magnesium titanate crystal lattice.