Glycothermal synthesis and photoluminescence of MgGa₂O ₄:Mn²⁺ nanophosphors: Comparison to ZnGa₂O ₄:Mn²⁺ nanophosphors

The photoluminescence (PL) intensity of MgGa₂O ₄:Mn²⁺ (MGM) nanophosphors synthesized by glycothermal reaction are ∼75 times higher than that of ZnGa₂O ₄:Mn²⁺ (ZGM) nanophosphors. We discuss this reason from the following points of view: (i) Mn contents, (ii) particle size, (iii) crystallinity, (iv) spontaneous pressure, (v) emission mechanism, and (vi) Mn²⁺ state. Judging from the results of the X-ray fluorescence analysis, transmission electron microscopy, X-ray diffractometry, PL spectroscopy, and electron paramagnetic resonance spectroscopy, the more homogeneous distribution of Mn²⁺ ions in the matrix of MGM is the predominant factor for determining the PL intensity. Mn²⁺ ions are more homogeneously incorporated into ZGM after post-heat-treatment at 1200°C for 1 h in Ar in comparison to MGM. This is explained by the geometrical reason: the order of ionic radius for tetrahedral coordination is Mg ²⁺ (71 pm) < Zn²⁺ (74 pm) < Mn²⁺ (80 pm). These results indicate that the glycothermal reaction promotes the incorporation of Mn²⁺ in MGM nanosphosphor, resulting in the higher PL intensity of MGM than that of ZGM. This is attributed to the formation of the low-crystallized MGM glycoxide precursor with the higher homogeneous mixture of different metallic ions.