Effects of solution pH value and mineralizer on formation and color property of holmium molybdate pigment via co-precipitation and sintering

A novel functional ceramic or glass pigment of monoclinic holmium molybdate (Ho2MoO6) with ‘allochroic effect’ was synthesized via co-precipitation and subsequent low-temperature sintering with different mineralizers (i.e., lithium chloride, sodium fluoride and boric acid). Effects of solution pH value and mineralizer type/content on Ho2MoO6 formation at different sintering temperatures and time were investigated. The results reveal that the solution pH value in co-precipitation reaction has an influence on the element ratio of Mo and Ho in the precursor and the pigment purity. The sintering temperature of forming sole Ho2MoO6 phase is decreased by 200 °C and the sintering duration is reduced in the presence of 5 wt % lithium chloride due to the decreased crystallization activation energy. Meanwhile, Ho2MoO6 pigment as powder or coating on ceramic tile and glass exhibits various colors (i.e., pale yellow, salmon, mustard and coral) under different illuminants (i.e., incandescent lamp A, solar-light D65, cool white fluorescent lamp F2 and three-band fluorescent lamp F11).