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In this paper, the photoluminescent properties of a lead-free double perovskite Cs 2 NaInCl 6 doped with Sb 3+ are explored. The host crystal structure is a cubic double perovskite with Fm 3̄ m symmetry, a = 10.53344(4) Å, and rock salt ordering of Na + and In 3+ . It is a wide bandgap compound ( E g ≈ 5.1 eV), and substitution with Sb 3+ leads to strong absorption in the UV due to localized 5s 2 → 5s 1 5p 1 transitions on Sb 3+ centers. Radiative relaxation back to the 5s 2 ground state, via a 3 P 1 → 1 S 0 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 Cs 2 SnCl 6 . The reduction in Stokes shift is likely due to a change in coordination number of Sb 3+ from 6-coordinate in Cs 2 NaInCl 6 to 5-coordinate in Cs 2 SnCl 6 . In addition to the high quantum yield, Cs 2 NaInCl 6 :Sb 3+ 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. 

Abstract There has been a great deal of recent interest in extended compounds containing Ru³⁺and Ru⁴⁺in light of their range of unusual physical properties. Many of these properties are displayed in compounds with the perovskite and related structures. Here we report an array of structurally diverse hybrid ruthenium halide perovskites and related compounds: MA₂RuX₆(X=Cl or Br), MA₂MRuX₆(M=Na, K or Ag;X=Cl or Br) and MA₃Ru₂X₉(X=Br) based upon the use of methylammonium (MA=CH₃NH₃⁺) on the perovskite A site. The compounds MA₂RuX₆with Ru⁴⁺crystallize in the trigonal space groupand can be described as vacancy‐ordered double‐perovskites. The ordered compounds MA₂MRuX₆with M⁺and Ru³⁺crystallize in a structure related to BaNiO₃with alternatingMX₆and RuX₆face‐shared octahedra forming linear chains in the trigonalspace group. The compound MA₃Ru₂Br₉crystallizes in the orthorhombic Cmcm space group and displays pairs of face‐sharing octahedra forming isolated Ru₂Br₉moieties with very short Ru–Ru contacts of 2.789 Å. The structural details, including the role of hydrogen bonding and dimensionality, as well as the optical and magnetic properties of these compounds are described. The magnetic behavior of all three classes of compounds is influenced by spin–orbit coupling and their temperature‐dependent behavior has been compared with the predictions of the appropriate Kotani models.