Synthesis of Metastable Silver-Lanthanide Double Perovskite Nanocrystals with White-Light Emission

Four silver-lanthanide double perovskite nanocrystals, namely, Cs₂AgSmCl₆, Cs₂AgEuCl₆, Cs₂AgGdCl₆, and Cs₂AgErCl₆, were synthesized for the first time. These four double perovskites have yet to be reported in any form and are found to be metastable in the bulk phase. By using the colloidal hot-injection synthesis method, the metastable double perovskite phase can be arrested kinetically. These lead-free nanocrystals show a broadband emission owing to the self-trapped exciton recombination, with Cs₂AgEuCl₆ exhibiting the characteristic f-f emission from Eu³⁺.