High-efficiency blue photoluminescence in the Cs2NaInCl6:Sb3+ double perovskite phosphor

Abstract

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 (E_g ≈ 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.