Doping concentration-dependent structural evolution and blue shift in indium-based organic–inorganic halide hybrids

Abstract

Despite the maturity of Sb³⁺ doping as a strategy for tuning structural and photophysical properties, inducing a configurational change of inorganic polyhedra solely by varying the dopant concentration remains highly challenging. Here, a series of indium-based halide hybrids (BZM)₃InCl₆:xSb³⁺ (BZM = benzimidazole, 0 ≤ x < 0.4) and (BZM)₅In₂Cl₁₁·H₂O:xSb³⁺ (0.4 ≤ x ≤ 0.7) were synthesized via a solvothermal method, enabling precise control over structural evolution and photoluminescence properties. Increasing the Sb³⁺ concentration progressively triggers a structural transition and an abnormal blue shift, with the emission color changing from orange to yellow. Comprehensive structural and optical analyses reveal that the subtle blue shift arises from local compressive distortion due to lattice reorganization from [In(Sb)Cl₆]³⁻ to [In(Sb)Cl₆·In(Sb)Cl₅]⁵⁻, which suppresses the extent of excited-state relaxation and slightly widens the band gap. This work demonstrates a crystal engineering approach to tailor the optical properties of hybrid luminescent materials through controlled doping, where the Sb³⁺-dependent luminescence stems from the coupled structural transformation and distortion, providing a robust route for photophysical engineering of metal halides toward versatile optical applications.