Near‐Infrared Emitting Lanthanide Catecholate Giant Single Crystals – Morphology Control and Photon Down‐Conversion

Abstract Lanthanide coordination polymers (Ln‐CPs), an intriguing type of near‐infrared (NIR) emitting materials, hold significant potential as fast‐response platforms in light‐emitting devices. The controlled crystallization of a series of Ln‐DHBQ (2,5‐dihydroxy‐1,4‐benzoquinone) CPs, yielding photoactive single crystals, is reported herein. Single crystal X‐ray diffraction analysis revealed the impact of the synthesis conditions employed on the structure of Ln‐DHBQ CPs. Hereby, the well‐known isostructural series of [Ln 2 (C 6 H 2 O 4 ) 3 (H 2 O) 6 ]·18H 2 O (Ln = Yb ( 1 ), Nd ( 3 )) is expanded with a novel member [Ln 2 (C 6 H 2 O 4 ) 3 (H 2 O) 4 ]·6H 2 O (Ln = Yb ( 2 )), that crystallizes in the monoclinic space group C 2/m instead of the trigonal space group R , which is typical of the parent series. Scanning electron microscopy and optical microscopy images showed that control over the size and morphology of Yb‐DHBQ and Nd‐DHBQ crystals was achieved, emerging as either disc‐like single crystals of up to 100 µm in size or faceted large single crystals up to 500 µm, respectively. This series of Ln‐DHBQ ( 1 − 3 ) features NIR photoluminescence with nanosecond lifetimes. Photon bunching is observed on the timescale of the excited‐state lifetime in the second‐order time correlation function, demonstrating a photon down‐conversion process for both Yb‐DHBQ CPs. This places Ln‐DHBQ crystals as excellent candidates for the development of operational platforms requiring intense and short period light emission read out cycles.