Investigation of structural profiles and lattice dynamics in Gd2O3-Based multication phosphorescent materials: Studies on crystal field splitting and photoluminescence characteristics

Abstract

Gd₂O₃:Eu³⁺: Li phosphors were synthesized via high-temperature solid-state reactions, revealing significant symmetry distortions and wavelength tuning to orange emissions upon lithium incorporation. Li⁺ ions introduced crystal field effects that favored electric dipole transitions. Rietveld refinement of X-ray diffractogram data (Li doping: 4 %–12 %) confirmed phase purity. Incorporating Li ⁺ ions into Eu³-doped Gd₂O₃ nanoparticles induced notable changes in lattice dynamics, evidenced by Raman mode evolution. Raman intensity increased up to 10 % Li doping and decreased beyond, indicating an optimal doping concentration for structural coherence. UV–Vis spectroscopy and Tauc plot analysis showed a red shift in the absorption edge and enhanced absorbance due to oxygen vacancies and interstitial defects. The optical bandgap narrowed from 5.71 eV (undoped) to 5.17–5.08 eV with Li doping, confirming defect-driven modulation of the electronic structure and improved energy transfer in the Eu³⁺-activated matrix. Photoluminescence spectra and CIE analysis revealed rare orange emissions from Eu³⁺. Judd–Ofelt (JO) theory was applied to assess the luminescent properties. JO parameters (Ω₂ and Ω₄), along with fluorescence lifetimes and radiative transition rates, validated the efficiency of the samples as orange emitters. Calculations showed Ω₂ values were consistently greater than Ω₄, indicating asymmetry in the local environment of the dopant, which enhances the relaxation of electric dipole selection rules. This asymmetry facilitates intense ⁵D₀ → ⁷F₂ transitions, accounting for the enhanced orange emission intensity. These findings suggest the samples as promising candidates for efficient orange-emitting phosphors.