Metal-oxide semiconductor-based flexible electronics are receiving widespread attention owing to their superior electrical properties and excellent stability. However, the main challenge in these materials is their ability to switch their responses in a reversible fashion. Currently, external stimuli (e.g. pressure, temperature) are applied on these materials to modify their optoelectronic properties via permanent structural distortion. The current work demonstrates the reversible tuning of nanophosphors using weak external fields (chemical dipoles). As a proof-of-concept, the adaptive optical properties of these materials are coupled with the rare-earth (RE) dopants for dynamic luminescent applications. Ni-doped TiO2 thin films, synthesized via sol-gel chemistry, were characterized to identify the effect of molecular dipoles (para-substituted benzoic acid ligands) on their optoelectronic properties. The local electronic structure changes around Ni2+ with the ligand were investigated via soft x-ray absorption spectroscopy (XAS) and in situ ultraviolet photoelectron spectroscopy (UPS), respectively. Upon functionalization with an electron-withdrawing ligand, a distinct shift in the t2g:eg filling was observed in the Ni LII edge XAS and was attributed to change in the electron density based on DFT simulations. Additionally, UPS results indicate that the direction of valence band bending is a function of the surface dipole moment, and the original state could be recovered due to the weak chemisorption of the ligands. Finally, a core-shell structure (Y2O3:Er3+|TiO2:Ni2+) was developed to facilitate energy transfer between the Ni and RE (Er3+) dopants for enhanced upconversion luminescence. The ligand-induced shifts in the optical absorption (~ 50 nm) and the emission spectra of these surface-modified core-shell phosphors were determined by UV-Vis and photoluminescence measurements. Additionally, the excited state energy transfer kinetics between the RE-TM ion couple were extracted from the lifetime decay measurements. Ultimately, these adaptive luminescent phosphors have the potential to reduce the RE dependence in light-emitting diodes, anti-counterfeit technologies, and bio-detection.

Reversible tuning of the pptoelectronic properties of transition metal doped oxide semiconductors for adaptive luminescence

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.