Novel yellowish-green single-phased spinel Mg_1−xBa_xAl₂O₄:Mn²⁺ phosphor(s) for color rendering white-light-emitting diodes

For white light-rendering research activities, interpretation by using colored emitting materials is an alternative approach. But there are issues in designing the white color emitting materials. Particularly, differences in thermal and decay properties of discrete red, green, and blue emitting materials led to the quest for the search of a single-phased material, able to emit primary colors for white light generation. The current study is an effort to design a simple, single-phase, and cost-effective material with the tunable emission of primary colors by a series of Mg_1−xBa_xAl₂O₄:Mn²⁺ nanopowders. Doping of manganese ion (Mn²⁺) in the presence of the larger barium cation (Ba²⁺) at tetrahedral-sites of the spinel magnesium aluminate (MgAl₂O₄) structure led to the creation of antisite defects. Doped samples were found to have lower bandgaps compared with MgAl₂O₄, and hybridization of 3d-orbitals of Mn²⁺ with O(2p), Mg(2s)/Al(2s3p) was found to be responsible for narrowing the bandgap. The distribution of cations at various sites at random results in a variety of electronic transitions between the valance band and oxygen vacancies as well as electron traps produced the antisite defects. The suggested compositions might be used in white light applications since they have three emission bands with centers at 516 nm (green), 464 nm (blue) and 622 nm (red) at an excitation wavelength of 380 nm. A detailed discussion to analyze the effects of the larger cationic radius of Ba²⁺ on the lattice strain, unit cell parameters, and cell volumes using X-ray diffraction analysis is presented.