Trivalent europium complex nanocrystals: fine-tuning luminescence properties with a micellar dipole vector shell for fingerprint development

Abstract

Eu(III) complexes are intrinsically highly luminescent materials. However, their luminescence is strongly quenched by solvent molecules. To address this issue, we herein present a micellar dipole vector shell strategy that prevents penetration of solvent molecules through the micellar shell and into the Eu(III) complex nanocrystals (NCs). The micellar dipole vector shell is constructed upon the formation of reverse micelles with an ordered arrangement of dipole amine-based surfactant molecules. The magnitude of the micellar dipole vector is finely tuned by methylation of octadecylamine (ODm). Going from N,N-dimethyloctadecylamine (DMODm) to N-methyloctadecylamine (MODm) and ODm, the magnitude of the dipole moment of the surfactant increases from 0.45 D to 0.99 D and 1.50 D, thereby establishing a higher barrier against penetration of solvent molecules, resulting in a reduction of nonradiative relaxation and an enhancement of radiative emission. As a result, the photoluminescence quantum yields (PLQY) of the Eu(III) complex (Eu-1) NCs increase from 4.6% to 12.4% and 15.1% and the exciton binding energy goes from 226.0 meV to 462.2 meV and then 542.2 meV. A potential application of this approach is confirmed with the construction of Eu(III) NCs from Eu-2. Overall, our results demonstrate that covering the trivalent europium complex NCs with a micellar dipole vector shell is a novel solution to enhance their luminescence.