Complexing Eu<sup>3+</sup>/Tb<sup>3+</sup> in a Nanoscale Postmodified Zr-MOF toward Temperature-Modulated Multispectrum Chromism
Sanchita Karmakar, Adrija Ghosh, Faruk Ahamed Rahimi, Bhawna Rawat, Tapas Kumar Maji
Abstract
In recent years, extensive research has been directed toward the successful preparation of nanoscale luminescent thermometers with high sensitivities operative in a broad temperature range. To achieve this goal, we have devised a unique design and facile multistep synthesis of Zr-ctpy-NMOF@TbxEuy compounds by confining Ln-complexes (Ln = Eu3+/Tb3+) into a robust nanoscale Zr-NMOF (MOF-808) via postsynthetic modification. Covalent grafting of 4-(4′-carboxyphenyl)-2,2′:6,2″terpyridine ligand (ctpy) with a high triplet state energy and corresponding immobilization of bimetallic Ln3+ ions resulted in yellow light-emitting [email protected] to achieve a sensitivity of 5.2% K–1 (thermal uncertainty dT < 1 K) operative over a broad temperature range of 25–400 K. To defeat the odds related to the detection of minute temperature changes using luminescent materials, we prepared a white light-emitting [email protected] that showed temperature-modulated multispectrum chromism where the color drastically changes from green (at 25 K, Q.Y.: 20.21%) to yellowish-green (at 200 K, Q.Y.: 23.13%) to white (at 300 K, Q.Y.: 26.4%) to orange (at 350 K, Q.Y.: 26.93%) and finally red (at 400 K, Q.Y.: 28.2%) with a high energy transfer efficiency of 49.8%, which is further supported by electron–phonon coupling.