Multi-color emission from lanthanide ions doped into niobium oxide

Abstract

The sol–gel process is a wet chemical methodology that uses compounds in the liquid state as starting reagents. After being transformed into a gel, the reagents can be molded into films, fibers, dense materials, or porous materials. The liquid-state reagents allow different compositions to be mixed, which gives rise to applications in various fields, including catalysis, biomaterials, photonics, and coatings. This study describes a way to produce phosphors based on niobium oxide doped with lanthanides ions by a non-hydrolytic sol–gel methodology for use in solid-state light emission. More specifically, the non-hydrolytic sol–gel route was used to prepare niobium oxide doped with La³⁺/Eu³⁺ or La³⁺/Tb³⁺ at different concentrations, which was followed by treatment at 550 or 900 °C. The X-ray diffraction (XRD) patterns revealed the presence of niobium oxide in the hexagonal, orthorhombic, and monoclinic phases. The lanthanide concentrations affected the niobium oxide crystalline structure interplanar spacing. The Raman spectra corroborated the XRD observations. The luminescence spectra showed that the niobium oxide matrix doped with lanthanides emitted at different wavelengths; the blue, the green, and the red emissions were ascribed to the matrix, Tb³⁺, and Eu³⁺, respectively. The samples doped with La³⁺ and Tb³⁺ or Eu³⁺ presented different colors in the chromaticity diagram. Energy was transferred between the niobium oxide matrix and the lanthanides ions, and the corresponding mechanisms were proposed. In conclusion, the niobium oxide matrix is an excellent host for application as light-emitting devices.