Solid state synthesis and luminescence of Zn2GeO4:Mn2+ phosphors using MnO2 as manganese source material: self-reduction of Mn4+ to Mn2+

We synthesized Zn2GeO4:Mn2+ phosphors using MnO2 as manganese source material by a solid state reaction in air condition. The Zn2GeO4:Mn2+ phosphors show green emission band corresponding to the 4T1 → 6A1 transitions of Mn2+. The green emission of Zn2GeO4:Mn2+ phosphors gives clear evidence for the substitution of Mn2+ to Zn2+ in Zn2GeO4 since Mn2+ presents green emission when it locates in a weak crystal field of four coordinated tetrahedron and there are only tetrahedral Zn2+ sites in Zn2GeO4. The existence of Mn2+ emission also suggests a self-reduction of Mn4+ to Mn2+ in the solid state reaction under air condition at high temperature. Based on the substitution in the phosphors, the self-reduction mechanism is speculated.