Synergy in the energy transfer between ligands and EuIII ions in molecular europium complexes: single-component white light-emitting luminogens

Abstract

Due to their structural flexibility and easy solution process capability, single-component white light-emitting pure organo-lanthanide complexes have been considered as promising candidates for solid-state lighting. Herein, we have reported a series of ancillary ligands, prepared by using imidazo-bipyridyl derivatives and dibenzoylmethane (DBM) as anionic ligands to synthesize ternary Eu(III) complexes, namely, Eu(DBM)₃L-mCF₃, Eu(DBM)₃L-pCF₃, Eu(DBM)₃L-pCH₃, and Eu(DBM)₃L-Naph-OCH₃. The photophysical and electrochemical properties of the ligands and their Eu(III) complexes were carefully investigated. The energy transfer mechanism was understood by combining experimental and theoretical calculations. Multiple emissions from both the ligand and the Eu(III) ions led to single-component white light emission. White light-emitting diodes (WLEDs) were fabricated by conjugating the Eu complexes with near UV LEDs. The results indicated superior performance, i.e., Commission Internationale de l'Éclairage (CIE) values of x = 0.33, y = 0.33, which were close to the National Television System Committee (NTSC) standard for pure white emission, correlated color temperature (CCT) of 5386 K and color rendering index (CRI) of 63%. The selected Eu complex was further coated on a blue LED chip and the corresponding white LED showed the following results: CIE (x = 0.36, y = 0.35), CCT (4234 K) and CRI (75%). In addition, taking advantage of the dual characteristic emission of the Eu complexes, the ratiometric sensing behavior was also explored. Eu(DBM)₃L-mCF₃ had a relative sensitivity value of 4.9% K⁻¹ at 323 K.