BaF2:Eu2+/3+,Tb3+ nanofibres achieve enhanced multicolor luminescence and white-light emission via multi-channel excitation and energy migration procedure

Abstract

A series of BaF₂:Eu^2+/3+ and BaF₂:Eu^2+/3+,Tb³⁺ one-dimensional (1D) nanofibres are devised and constructed by using electrospinning and di-crucible fluorination technology without applying reducing gas and protective gas. During the formation process of 1D Eu-doped BaF₂ nanofibres, partial reduction of Eu³⁺ is realized, resulting in the co-existence of Eu²⁺ and Eu³⁺ in the specimen, which is responsible for multicolor luminescence. In the emission spectra of BaF₂:Eu^2+/3+ nanofibres, the broad peak centered at 377 nm (5d → 4f) belongs to Eu²⁺ ions and the narrow peaks at 592 (⁵D₀ → ⁷F₁) and 613 nm (⁵D₀ → ⁷F₂) belong to Eu³⁺ ions. Concurrently, BaF₂:Eu^2+/3+ nanofibres directly emit luminous color from the blue-light to the yellow-light region by applying different wavelength excitation. Furthermore, by doping green-light-emitting Tb³⁺ into the BaF₂:Eu^2+/3+ nanofibres to acquire BaF₂:Eu^2+/3+,Tb³⁺ nanofibres, white-light emission and multicolor luminescence, covering the whole visible light area, are facilely realized via the multi-mode regulation of Eu ion valence states, Eu^2+/3+ and Tb³⁺ concentrations, the energy transfer among Eu^2+/3+ and Tb³⁺, and excitation wavelengths, thereby greatly improving the practicability of the neoteric luminescent material. Furthermore, the mechanisms of multicolor luminescence and white-light emission are systematically studied, and the Eu²⁺ → Tb³⁺ → Eu³⁺ energy transfer process in BaF₂:Eu^2+/3+,Tb³⁺ nanofibres is further improved and clarified. These new findings are helpful to design and fabricate new types of rare earth-based 1D luminescent nanostructures.