Molecular and Self-Trapped Excitonic Contributions to the Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems

摘要

The present solid state lighting (SSL) technology is based on using a combination of phosphors to give the desired white light emitting devices. The property of broadband emission from a single phosphor is not only difficult to achieve but also poses a challenge in device fabrication. Hybrid organic–inorganic perovskites especially in low dimensions (2D/1D) are being widely explored for their optoelectronic properties. Few of these materials exhibit broadband emission upon ultraviolet excitation, providing a scope for synthetic engineering in achieving commercially viable singlephosphor materials. In this work, three interesting diammonium-based lowdimensional hybrid perovskites for broadband photoluminescence (PL) are examined. The doubly protonated ethylenediamine-configured monoclinic (P2_1/n) 1D ribbon assembly (H_3N-CH_2-CH_2-NH_3)_8(Pb_4Br_(18)) · Br_6 (1) and the orthorhombic (Pbcm) 2D-twisted octahedral (H_3N-CH_2-CH_2-NH_3) (Pb_2Cl_6) (2) show white luminescence, while the doubly protonated piperazine-configured orthorhombic (Pnnm) 0D dual-octahedral (C_4N_2H_(12))4(Pb_2Br_(11)) · (Br)(H_2O)_4 (3) exhibits bluish-white luminescence. Based on the PL of the organic diammonium salt, the time-resolved PL, Raman signatures, and density functional theory (DFT) calculations, it is shown that the broadband luminescence has dual origin: one around 400 nm from diammonium-related molecular fluorescence and another around 516 nm from self-trapped excitons. The structure-specific relative contributions and interplay between the two define the overall character of the broadband luminescence.