(388d) Reversible Tuning of the Optoelectronic Properties of Transition Metal Doped Semiconductor Materials for Adaptive Luminescence
AIChE Annual Meeting
2019
2019 AIChE Annual Meeting
Materials Engineering and Sciences Division
Area 8E (Electronic and Photonic Materials) Graduate Student Award Session (Sponsored by JVST)
Tuesday, November 12, 2019 - 4:45pm to 5:10pm
Ni doped TiO2 thin films, synthesized via sol-gel chemistry, were characterized to identify effect of surface dipoles (para-substituted benzoic acid ligands) on their optoelectronic and structural properties. The local structural and electronic 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 and energy levels were observed in the Ni LII edge XAS spectra and was attributed to a local geometry distortion with a change in the electron density based on DFT simulations. Additionally, the direction of the valence band bending and valence band electronic structure of the TiO2:Ni2+ thin films was characterized with UPS. The bending was observed to be a function of the surface dipole and coverage, and the original state could be recovered due to the weak chemisorption of the benzoic-acid ligand molecules on the surface of the TiO2:Ni2+. Finally, a core-shell structure was synthesized to facilitate energy transfer between the Ni and RE dopants for enhanced upconversion luminescence. Er3+ doped NaYF4 nanoparticles were synthesized as the core NPs using colloidal chemistry and Ni2+ doped shell layer was coated to have ligand dependent absorption. 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 (PL) measurements. Additionally, the excited state energy transfer kinetics between the Er-Ni 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, bio-detection, etc.