Mn3+ in Trigonal Bipyramidal Coordination: A New Blue Chromophore

Abstract

We show that trivalent manganese, Mn³⁺, imparts an intense blue color to oxides when it is introduced at dilution in trigonal bipyramidal coordination. Our optical measurements and first-principles density functional theory calculations indicate that the blue color results from an intense absorption in the red/green region. This absorption is due in turn to a symmetry-allowed optical transition between the valence-band maximum, composed of Mn 3d_x²−y²,xy states strongly hybridized with O 2p_x,y states, and the narrow Mn 3d_z²-based conduction-band minimum. We begin by demonstrating and explaining the effect using a well-defined prototype system: the hexagonal YMnO₃−YInO₃ solid solution. We then show that the behavior is a general feature of diluted Mn³⁺ in this coordination environment.