Upconversion and multiexciton generation in organic Mn(II) complex boost the quantum yield to > 100%

Abstract

Highly efficient, low-cost, and eco-friendly fluorescent bulk materials showing the quantum confinement effect with both upconversion (UC) and multiexciton generation (MEG) are promising for optoelectronic devices. Yet, these combined phenomena have not been realized in bulk organic-inorganic single crystals (SCs). MEG by low-energy photons remains a critical challenge for generating multiexcitons. Herein, we report non-toxic, zero-dimensional (0D) bulk organic-inorganic hybrid, green light-emitting SCs of [Me3NPh](2)MnBr4 (1) (Ph: phenyl), which show both UC and MEG along with a long lifetime (400 mu s). This is supported by many-body theory predicting a large exciton binding energy (483 meV), upon excitation by band-gap energy (2.62 eV) photons. The MEG in 1 contributes to the photoluminescence (PL) quantum yield (QY) of up to 189%, the highest among any 0D hybrid or other single crystals. Our findings will pave the way to design and synthesize lead-free 0D hybrid materials having UC and MEG properties, improving the performances of solar cells, LEDs, and other optoelectronic devices.