Ternary sulfides ALnS₂:Eu²⁺ (A = Alkaline Metal, Ln = rare-earth element) for lighting: Correlation between the host structure and Eu²⁺ emission maxima

Ternary sulfides ALnS₂ (A = Alkaline Metal, Ln = rare-earth element) doped with the Eu²⁺ ions are characterized by a very wide range of tunability of the Eu²⁺ emission maxima with the host's chemical composition. In the present work, a detailed analysis of the structural properties of these materials was performed. It was shown that their lattice constants can easily be expressed as the linear functions of the ionic radii and electronegativities of the constituting elements. As a further step, the relations between the structural properties of the hosts and optical properties of the Eu²⁺ dopant were analyzed. It was demonstrated that the position of the Eu²⁺ emission maxima is a linear function of the so-called hexagonality ratio c/a, where c and a are the lattice constants of the rhombohedral ternary sulfides. The obtained results can be used as helpful guides for manufacturing Eu²⁺-doped ternary sulfides with desired emission properties with high potential for white LEDs applications.