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

S. Sekar, J. George Muller, J. Karthikeyan, P. Murugan, N. Lakshminarasimhan*

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

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:xEu(3+) 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.

Original languageEnglish
Pages (from-to)19087-19097
Number of pages11
JournalPhysical Chemistry Chemical Physics
Volume20
Issue number28
DOIs
Publication statusPublished - 28 Jul 2018
MoE publication typeA1 Journal article-refereed

Keywords

  • CADMIUM SELENIDE NANOCRYSTALS
  • LIGHT EMISSION
  • QUANTUM DOTS
  • EU3+ IONS
  • SPECTROSCOPY
  • NANOPARTICLES
  • FLUORESCENCE
  • SURFACES
  • CRYSTAL
  • SPINELS

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