Li2MnO3: a rare red-coloured manganese(iv) oxide exhibiting tunable red–yellow–green emission

Abstract

An experimental assessment of Li₂MnO₃ has been conducted, in conjunction with related Mn(IV) oxides, to investigate its red colour and photoluminescence. Optical absorption spectra revealed strong band gap absorption, with a sharp edge at ∼610 nm and a transparent region between ∼610 and ∼650 nm, giving rise to the red colour of this compound. Octahedral Mn(IV) ligand field transitions have been observed in the excitation spectra of Li₂MnO₃, corresponding both to Mn(IV) at ideal sites and displaced in Li sites in the rock salt-based layered structure of Li₂MnO₃. Optical excitation at ligand field transition energies produces tunable emission in the red–yellow–green region, rendering Li₂MnO₃ a unique Mn(IV) oxide. The honeycomb-ordered [LiMn₆] units in its structure are probably the origin of both the absorption and the photoluminescent properties of Li₂MnO₃.