Hetero Atom (Nitrogen) replaced by Phenyl Insertion in Molecular Eu-complex Facilitated Sun Light-like Emission for Sustainable White LEDs and Non-Contact Thermometer

Abstract

To enhance the quality of white light (mimicking sunlight-like emission) for solid-state lighting (SSL) applications, a novel imidazolyl-bipyridyl ligand was designed as an ancillary ligand to achieve multi-coloured emission in the Europium (III) complex. The structural engineering in the case of the ligand was crafted by replacing the nitrogen heteroatom with a phenyl moiety to shift the broad green emission (λ = 553 nm) into a narrow blue emission (λ = 460 nm). This blue emission of ligand, when combined with Europium (III) using thenoyltrifluoroacetone (TTA) and dibenzoylmethane (DBM) as anionic ligands, helped to achieve white light emission by exciting with near-UV LED (λex = 390 nm), which had a great advantage to get white emission colour without blue LED (λex = 460 nm). Density Functional Theory (DFT) calculations were performed to theoretically investigate the energy transfer process from the ligand to the emitting level (5D0) of Eu3+ in Eu complexes. These Europium (III) complexes exhibit a unique dual-emissive behaviour (multi-coloured emission), including white emission across various solvents. The Eu(III) complexes have shown excellent properties in a white LED, with a Commission Internationale de l'Éclairage (CIE) coordinate (x = 0.30, y = 0.32), and serve as a functional luminescent thermometer, displaying a colour change with a temperature rise.