Stimuli-responsive photoluminescent copper(I) halides for scintillation, anticounterfeiting, and light-emitting diode applications

Abstract

Highly sensitive stimuli-responsive luminescent materials are crucial for applications in optical sensing, security, and anticounterfeiting. Here, we report two zero-dimensional (0D) copper(I) halides, (TEP)₂Cu₂Br₄, (TEP)₂Cu₄Br₆, and 1D (TEP)₃Ag₆Br₉, which are comprised of isolated [Cu₂Br₄]²⁻, [Cu₄Br₆]²⁻, and [Ag₆Br₉]³⁻ polyanions, respectively, separated by TEP⁺ (tetraethylphosphonium [TEP]) cations. (TEP)₂Cu₂Br₄ and (TEP)₂Cu₄Br₆ demonstrate greenish-white and orange-red emissions, respectively, with near unity photoluminescence quantum yields, while (TEP)₃Ag₆Br₉ is a poor light emitter. Optical spectroscopy measurements and density-functional theory calculations reveal that photoemissions of these compounds originate from self-trapped excitons due to the excited-state distortions in the copper(I) halide units. Crystals of Cu(I) halides are radioluminescence active at room temperature under both X- and γ-rays exposure. The light yields up to 15,800 ph/MeV under 662 keV γ-rays of ¹³⁷Cs suggesting their potential for scintillation applications. Remarkably, (TEP)₂Cu₂Br₄ and (TEP)₂Cu₄Br₆ are interconvertible through chemical stimuli or reverse crystallization. In addition, both compounds demonstrate luminescence on-off switching upon thermal stimuli. The sensitivity of (TEP)₂Cu₂Br₄ and (TEP)₂Cu₄Br₆ to the chemical and thermal stimuli coupled with their ultrabright emission allows their consideration for applications such as solid-state lighting, sensing, information storage, and anticounterfeiting.