Manganese(II) in Tetrahedral Halide Environment: Factors Governing Bright Green Luminescence

Finding narrow-band light emitters for the visible spectral region remains an immense challenge. Such phosphors are in great demand for solid-state lighting and display application. In this context, green luminescence from tetrahedrally coordinated Mn(II) is an attractive research direction. While the oxide-ligand environment had been studied for decades, much less systematic efforts have been undertaken with regard to halide coordination, especially in the form of fully inorganic halide matrixes. In this study, we synthesized a series of hybrid organic-inorganic Mn(II) halides as well as a range of fully inorganic Zn halide hosts (chlorides, bromides, iodides) doped with Mn(II). In the latter, tetrahedral coordination is attained via substitutional doping owing to the tetrahedral symmetry of Zn sites. We find that the choice of the halide as well as subtle details of the crystal structure profoundly govern the photoluminescence peak positions (500-550 nm range) and emission line widths (40-60 nm) as well as radiative lifetimes (shorter for iodides) through the altered ligand-field effects and degrees of spin-orbit coupling. The photoluminescence quantum yields were as high as 70-90%. The major hurdle for the practical use of these compounds lies in their low absorption coefficients in the blue spectral regions.