Doping Metal Ions into Cs2AgInCl6 Halide Double Perovskites

Abstract

Lead halide perovskites have been rising as a potential candidate for photovoltaic (PV) and light emitting diode applications due to their impressive optical and optoelectronic properties. However, their commercialization confronts major issues like moisture and thermal instability and Pb toxicity. Recent development of lead-free halide double perovskites (HDPs), A2BICIIIX6 by substituting the divalent cation Pb2+ with a monovalent and a trivalent cation have been suggested to overcome the above concerns. But most HDPs have either indirect or wide band gaps with weak photoluminescence (PL) emissions limiting their optical applications. Recently reported Cs2AgInCl6 HDPs exhibit direct band gap as well as inherent crystal stability but they have a wide band gap (3.5 eV). They also have a very less intense, broad, defect mediated emission in the lower energy region of visible spectrum. Hence tailoring the optical emission of Cs2AgInCl6 was necessary. Here I report the synthesis and characterization of metal ion doped Cs2AgInCl6 double perovskites. Doping of Mn2+ transition metal ions into the Cs2AgInCl6 host lattice imparted an intense emission at red region (632 nm) due to the spin forbidden 4T1 - 6A1 transition of Mn d electrons. PL decay for doped samples revealed sub millisecond lifetime accounted for the spin forbidden transitions of isolated Mn2+ dopants. A hyperfine splitting constant of 8.5 mT confirms the incorporation of Mn2+ into Cs2AgInCl6 lattice. Lanthanide ions doping (Eu2+ and Sm3+) were carried out expecting sharp and intense multicolor emission in Cs2AgInCl6 host. Also Cs2AgIn(Cl/Br)6 mix HDP synthesis was attempted for developing a direct band gap material with suitable band gap for PV application.