Energy transfer cooperation between ligands and EuIII ions in molecular europium complexes for vapoluminescence sensing (reversible on/off emission switching) and hybrid white LED/plant-growth applications

Abstract

In a europium complex, two ancillary ligands were designed to provide complete energy transfer to the Eu(III) ion. Both ligands were successfully synthesized and utilized for europium complexation (Eu(TTA)₃-phen-fl-mCF₃, Eu(TTA)₃-phen-fl-pCH₃, Eu(DBM)₃-phen-fl-mCF₃, and Eu(DBM)₃-phen-fl-pCH₃). The ligands display deep blue emission, whereas their corresponding europium complexes exhibit pure red emission (⁵D₀ → ⁷F₂, electric dipole transition). Photophysical and electrochemical analyses were carried out in detail. The theoretical and experimental studies confirmed that complete energy transfer occurred from the ligands to the Eu(III) ion. The color purity was also calculated for the complexes, among them, the Eu(TTA)₃-phen-fl-mCF₃ complex showed the highest color purity (98.36%). The pure red emissive Eu-complexes were integrated with near UV light emitting diodes (LEDs) to fabricate a red LED. The Eu(TTA)₃-phen-fl-mCF₃ complex was blended with yellow dye conjugated on a blue LED to produce a white LED, the white LED showed warm white light with CIE (x = 0.336; y = 0.377) and lower CCT (5360 K) and superior CRI (81) values. The hybrid deep-red-LED was fabricated to study a plant cultivation application, the EL spectrum entirely covered the phytochrome Pr absorption spectrum. Also, a film of Eu-complex revealed on–off–on luminescence performance under an atmosphere of acid–base. The combination of Eu(III) complex + NaSrGd(MoO₄)₃:Sm³⁺ orange red phosphor based deep-red LED showed prominent coverage of the absorption spectrum of phytochrome Pr.