Controlling Light Emission in Multinary Copper(I) Halides for Advanced Optoelectronic Applications

Among the lead-free hybrid luminescent materials, hybrid organic-inorganic Cu(I) halides are getting increased attention due to their low cost, nontoxic and earth abundant elemental compositions, and ability of Cu(I) to form variable coordination patterns and geometries. In this work, we demonstrate that adaptable and flexible organic cations such as C₈H₂₀P⁺ (as opposed to rigid aromatic cations) can lead to structural diversity by stabilizing multiple structural building blocks. We found that the anionic structural building blocks in (C₈H₂₀P)₂Cu₂Br₄ and (C₈H₂₀P)₂Cu₄Br₆ are composed of edge-sharing dimeric trigonal planar units [Cu₂Br₄]^2- and star-shaped cluster units [Cu₄Br₆]^2-, respectively. (C₈H₂₀P)₂Cu₂Br₄ and (C₈H₂₀P)₂Cu₄Br₆ exhibit bright greenish-white and orange emission with photoluminescence quantum yield (PLQY) values >90%. Optical spectroscopy measurements and computational results reveal that photoemission in (C₈H₂₀P)₂Cu₂Br₄ and (C₈H₂₀P)₂Cu₄Br₆ originate from self-trapped excitons due to the excited state distortions in the inorganic units.
Besides, to bring emission tunability in a single component copper(I) halide, the inclusion of Mn²⁺ in (C₈H₂₀P)₂Cu₄Br₆ resulted in the formation of a new compound (C₈H₂₀P)₄Cu₄MnBr₁₀. In this work, we showed that both Mn²⁺ and Cu⁺ can act as distinct optical active sites in bimetallic halide system and the resultant material can generate dual band emission (covering 450 nm to 850 nm) providing wide spectral tunability. This novel bimetallic copper(I) halide exhibits bright green and yellow emission with PLQY values of ~80% and ~50% under 465 nm and 395 nm excitation, respectively. The investigation of the excited state dynamics of (C₈H₂₀P)₂Cu₄Br₆ is ongoing and will be reported in due course.
These three novel hybrid copper(I) halides demonstrate promising radioluminescence at room temperature under both X- and γ-rays, suggesting their potential for scintillation applications. Moreover, the sensitivity of (C₈H₂₀P)₂Cu₂Br₄, (C₈H₂₀P)₂Cu₄Br₆ and (C₈H₂₀P)₄Cu₄MnBr₁₀ to the chemical and/or thermal stimuli coupled with their ultrabright light emission allows their consideration for multiple optoelectronic applications such as photodetection, solid-state lighting, high-level security sensing, multi-modal anticounterfeiting, and information storage. Notably, a UV solar blind photodetector based on (C₈H₂₀P)₂Cu₂Br₄ demonstrates external quantum efficiency up to 53%.
Overall, fundamental understanding of the structure-property relationships in these novel materials will eventually help to design and develop future copper(I) based photoluminescent materials with better tunability of the optical properties for desirable optoelectronic applications.