Magnesium Halides as a Lead-free Family with Unique Optoelectronic Properties

The metal halides have superior optoelectronic properties because of their special electronic structures, such as the ns2 metal halides (Pb2+, Sb3+, Sn2+, etc.) and dx metal halides (Zn2+, Cd2+, Mn2+, etc.). The Mg halides, which have unfriendly electronic structures with high excited state energy levels, conflicts with the basic requests of luminescent metal halides. Here we found efficient luminescent properties for the Mg halides. A series of Mg halides have been synthesized and studied. Under ultraviolet (UV) excitation, Li2MgCl4 and RbMgCl3 exhibit violet light emissions at 350 nm and 430 nm, CsMgCl3 and Cs2MgCl4 exhibit blue light emissions at 465 nm and 480 nm. CsMgCl3, RbMgCl3, and Li2MgCl4 show high thermal stability due to the strong rigidity of the crystal structures. With the doping of Mn(II) ions into the Mg sites, their emission colors could be further tuned. Based on the unique photoluminescence of the Mg halides, we have successfully applied the as-synthesized materials into green lighting and anti-counterfeiting devices. Our study shows that Mg halides are also a family worthy studying, shedding light on the exploration of metal halides as efficient optoelectronic semiconductors.