Elusive double perovskite iodides. Structural, optical, and magnetic properties

Halide double perovskites [A${}_2$M${}^I$M${}^{III}$X${}_6$] are an important class of materials that have garnered substantial interest as non-toxic alternatives to conventional lead iodide perovskites for optoelectronic applications. While numerous studies have examined chloride and bromide double perovskites, reports of iodide double perovskites are rare, and their definitive structural characterization has not been reported. Predictive models have aided us here in the synthesis and characterization of five iodide double perovskites of general formula Cs${}_2$NaLnI${}_6$ (Ln=Ce, Nd, Gd, Tb, Dy). The complete crystal structures, structural phase transitions, optical, photoluminescent, and magnetic properties of these compounds are reported. (© 2023 Wiley-VCH GmbH)