Discovery of novel inorganic Mn5+-doped sky-blue pigments based on Ca6BaP4O17: Crystal structure, optical and color properties, and color durability

Novel inorganic sky-blue pigments, Ca6Ba(P1-xMnx)4O17 (0 ≤ x ≤ 0.13) were synthesized in a single phase form by a conventional solid-state reaction method and their color properties were investigated in the detail. The pigments exhibited strong optical absorption in the UV and the yellow-red light regions due to the CT transition in MnO4 tetrahedra and the DMSO-d6 transitions of Mn5+, which is the origin of the sky-blue color. The optimization of the composition resulted in the attainment of the highest sky-blue hue for the Ca6Ba(P0.99Mn0.01)4O17, where the L*, a*, b*, C, and H° values are 75.47, −11.67, −10.29, 15.6, and 221.4°, respectively. These pigments showed a low chemical stability of color for acid/alkali solution, whereas the pigments showed an excellent color durability for heat and light. Although they are required to improve the chemical stability of color, the present pigment could be an attractive candidate as a novel environment friendly inorganic sky-blue pigment.