Bright Blue and Green Luminescence of Sb(III) in Double Perovskite Cs₂MInCl₆ (M = Na, K) Matrices

The vast structural and compositional space of metal halides has recently become a major research focus for designing inexpensive and versatile light sources; in particular, for applications in displays, solid-state lighting, lasing, etc. Compounds with isolated ns²-metal halide centers often exhibit bright broadband emission that stems from self-trapped excitons (STEs). The Sb­(III) halides are attractive STE emitters due to their low toxicity and oxidative stability; however, coupling these features with an appropriately robust, fully inorganic material containing Sb³⁺ in an octahedral halide environment has proven to be a challenge. Here, we investigate Sb³⁺ as a dopant in a solution-grown metal halide double perovskite (DP) matrix, namely Cs₂MInCl₆:xSb (M = Na, K, x = 0–100%). Cs₂KInCl₆ is found to crystallize in the tetragonal DP phase, unlike Cs₂NaInCl₆ that adopts the traditional cubic DP structure. This structural difference results in distinct emission colors, as Cs₂NaInCl₆:xSb and Cs₂KInCl₆:xSb compounds exhibit broadband blue and green emissions, respectively, with photoluminescence quantum yields (PLQYs) of up to 93%. Spectroscopic and computational investigations confirm that this efficient emission originates from Sb­(III)-hosted STEs. These fully inorganic DP compounds demonstrate that Sb­(III) can be incorporated as a bright emissive center for stable lighting applications.