High-efficiency blue photoluminescence in the Cs2NaInCl6:Sb3+ double perovskite phosphor†
In this paper, the photoluminescent properties of a lead-free double perovskite Cs2NaInCl6 doped with Sb3+ are explored. The host crystal structure is a cubic double perovskite with Fmm symmetry, a = 10.53344(4) Å, and rock salt ordering of Na+ and In3+. It is a wide bandgap compound (Eg ≈ 5.1 eV), and substitution with Sb3+ leads to strong absorption in the UV due to localized 5s2 → 5s15p1 transitions on Sb3+ centers. Radiative relaxation back to the 5s2 ground state, via a 3P1 → 1S0 transition, leads to intense blue luminescence, centered at 445 nm, with a photoluminescent quantum yield of 79%. The Stokes shift of 0.94 eV is roughly 33% smaller than it is in the related vacancy ordered double perovskite Cs2SnCl6. The reduction in Stokes shift is likely due to a change in coordination number of Sb3+ from 6-coordinate in Cs2NaInCl6 to 5-coordinate in Cs2SnCl6. In addition to the high quantum yield, Cs2NaInCl6:Sb3+ exhibits excellent air/moisture stability and can be prepared from solution; these characteristics make it a promising blue phosphor for applications involving near-UV excitation.