Nanotunnel Structures within Metal Oxides Induce Active Sites for the Strong Self-Reduction of Mn^IV to Mn^II

Zn₂SiO₄, Zn₂GeO₄, and CdAl₂O₄ possess high electron density in their six-membered-ring nanotunnels, manganese from MnO₂ was successfully doped into them, and green or blue phosphors were produced in air. It is nanotunnel A with high electron density that induces active sites for the reduction of Mn^IV. Mn^IV is captured and reduced to Mn^II on active sites by seizing two electrons from native defect V_O^× (V_O^× + Mn⁴⁺ → V_O^·· + Mn²⁺). CdB₄O₇:0.02Mn²⁺ was also synthesized from MnO₂ or MnCO₃ to confirm the role of nanotunnels. Such inorganic crystals with unique nanotunnel structure may bring more amazing performances in the field of materials in the future.