Unveiling the multifunctional roles of hitherto known capping ligand oleic acid as blue emitter and sensitizer in tuning the emission colour to white in red-emitting phosphors

Abstract

Capping ligands are vital in stabilizing various nanostructures and semiconductor quantum dots in which unusual optical properties, especially white light emission, have been realized. Oleic acid (OA) is a widely used capping ligand. Here, we report blue emission from OA in its free molecular form and further demonstrate this by anchoring OA over the surfaces of Al2O3, ZnAl2O4(ZA), ZnAl2O4:Eu3+ (ZA:Eu3+), and Y2O3:Eu3+. White light emission was observed from OA-modified ZA:Eu3+ nanophosphor due to mixing of broad blue emission of OA and red emission of Eu3+ through energy transfer from OA to Eu3+. A detailed study revealed the characteristic binding modes of OA and their dependence on Eu3+ concentration, structural inversion in ZA, and the optical properties and surface states in the pristine and OA-modified ZA:Eu3+. First principles density functional theory calculations were employed to provide an insight into the HOMO-LUMO levels of OA molecule and, electronic structure of pristine and OA-modified ZA surface. The binding of OA with the ZA:xEu3+ surface changes from bridging bidentate to chelating bidentate with increasing Eu3+ concentration in the lattice. The surface binding nature of the carboxylate group with the optimized surface of ZA and the creation of mid-gap states were deduced theoretically by using butanoic acid instead of OA. The blue emission from OA and its mixing with Eu3+ emission was further confirmed experimentally by anchoring it over Y2O3:Eu3+ red phosphor. These results show the multifunctional roles of OA as capping ligand, blue emitter and sensitizer in tuning the emission colour of red phosphors into white.

Interfacial Modification of Photoanode|Electrolyte Interface Using Oleic Acid Enhancing the Efficiency of Dye-Sensitized Solar Cells

“…This enhanced absorbance can be attributed to the creation of surface states as observed in the case of OA-anchored ZnAl 2 O 4 :Eu 3+ and BiPO 4 :Eu 3+ phosphors. 19,22 To clearly observe this, the DRUV–vis spectrum of OA-modified TiO 2 was recorded using pristine TiO 2 as baseline reference. The spectrum obtained is the difference spectrum and shows only the absorbance from the surface states created because of anchoring of OA over TiO 2 surface.…”

“…As mentioned earlier, OA also acts as an emitter and a sensitizer. 19 Hence, understanding the optical properties of OA and its interaction with N719 dye will provide further insights into the observed enhancement in the PCE. The photoluminescence (PL) emission spectrum of OA while being monitored using 365 nm excitation wavelength falls in the blue region of visible spectrum (Figure 7A) where N719 dye absorbs.…”

“…18 Recently, OA has also been shown as a blue emitter and a sensitizer of rare-earth luminescent centers when anchored over different oxide surfaces. 19 Thus, it is important to understand the role of OA that is anchored over dye-adsorbed TiO 2 surface and its implications on DSSC performance.…”

“…18 Recently, OA has also been shown as a blue emitter and a sensitizer of rare-earth luminescent centers when anchored over different oxide surfaces. 19 Thus, it is important to understand the role of OA that is anchored over dye-adsorbed TiO 2 surface and its implications on DSSC performance. Hence, the interfacial engineering of photoanode to overcome the V OC −J SC trade-off, suppress the recombination losses, enhance the charge injection rate from sensitizer to semiconductor, and understand the mechanisms of the aforementioned phenomena will help in designing DSSCs with higher PCE.…”

“…OA-capped TiO 2 was used in DSSC along with resorcinol-based Ru­(II)–Re­(I) complexes and higher electron lifetimes were observed because of the resorcinol binding . Recently, OA has also been shown as a blue emitter and a sensitizer of rare-earth luminescent centers when anchored over different oxide surfaces . Thus, it is important to understand the role of OA that is anchored over dye-adsorbed TiO 2 surface and its implications on DSSC performance.…”