NaGdF4:Eu3+ nanocrystalline: an in-depth study of energy transfer processes and Judd-Ofelt analysis using the luminescence excitation spectrum

Abstract

NaGdF₄ nanocrystalline doped with different concentrations of Eu³⁺ ions were synthesized using the precipitation method. The structure and morphology of the material were investigated through the measurements of the XRD patterns and SEM images, respectively. The optical properties of the NaGdF₄:Eu³⁺ nanocrystalline were studied in the framework of the Judd-Ofelt theory in which the Ω_λ parameters were calculated by two methods: the traditional method using the luminescence spectra and the self-referenced method using the luminescence excitation spectra. In NaGdF₄:Eu³⁺ nanocrystalline, the Gd³⁺ ions in the lattice act as sensitizer centers for the luminescence of Eu³⁺ ions under excitation at 272 and 310 nm. The energy transfer process from Gd³⁺ to Eu³⁺ causes the emission enhancement of Eu³⁺ ions. Upon excitation by the characteristic wavelengths of Gd³⁺, the luminescence efficiency of the Eu³⁺ ions in NaGdF₄:Eu³⁺ is affected by two mechanisms: the emission of Gd³⁺ ions and the trapping of excited energy by the Eu³⁺ ions. The energy transfer between Eu³⁺ ions was also discussed in detail. This process leads to the enhancement of the luminescence bands originating from the ⁵D₀ level. The dominant interaction between the Eu³⁺ ions in the energy transfer process is the dipole-dipole mechanism, which is determined by fitting the decay curve of the ⁵D₂ level to the Inokuti-Hirayama model.