Cryptomelane (K-OMS-2) (K(Mn 4+ , Mn 2+ ) 8 O 16 ) is a manganese-oxide mineral that is abundant in soils and rock coatings globally and is gaining importance in materials science and industrial mineralogy. The crystal structure is composed of 2 × 2 octahedra that creates a tunnel space for K + . Low-weight percent (wt%) europium (Eu)-doped, high-wt% Eu-doped, low-wt% cerium (Ce)-doped, and high-wt% Ce-doped cryptomelane were...