Anomalous intense emission of the 5D0/7F4 transition for reddish-orange light-emitting and fluorescent probe for multiple lattice sites in β-PbF2:Eu3+/K+ oxyfluoride glass ceramics†

Herein, β-PbF₂:Eu³⁺/K⁺ glass ceramics (GCs) were synthesized and characterized by X-ray diffraction (XRD), photoluminescence (PL) and decay curves. Based on the XRD analysis, it was inferred that Eu³⁺ and K⁺ ions were doped in the β-PbF₂ lattice by substituting Pb²⁺ ions. Compared with the interstitial fluorine (F_i⁻) (Eu³⁺ + F_i⁻ = Pb²⁺), K⁺ substitutional doping (Eu³⁺ + K⁺ = 2Pb²⁺) was the preferential charge-compensating mechanism with the introduction of K⁺ ions in the β-PbF₂:Eu³⁺ GCs. Consequently, this is the first report on the anomalous emission of the ⁵D₀/⁷F₄ transition in β-PbF₂:Eu³⁺ GCs. Based on this anomalous ⁵D₀/⁷F₄ transition, a new lattice site with D_4d symmetry occupied by Eu³⁺ ions was proposed for the first time in β-PbF₂:Eu³⁺ GCs. Moreover, according to the intensity ratio of I(⁵D₀/⁷F₀)/I(⁵D₀/⁷F₂) (I₀₀/I₀₂), I(⁵D₀/⁷F₂)/I(⁵D₀/⁷F₁) (I₀₂/I₀₁) and I(⁵D₀/⁷F₄)/I(⁵D₀/⁷F₁) (I₀₄/I₀₁), the breaking of the local lattice symmetry around the Eu³⁺ ions induced by K⁺ ions was demonstrated in detail. With the introduction of K⁺ ions in β-PbF₂:Eu³⁺ GCs, the local lattice symmetry around the Eu³⁺ ions continued to decrease from O_h to D_4d, C_4v, C_3v, C_2v, and C₁. Due to the effective charge-compensation of the K⁺ ions, we successfully realized the adjustment and enhancement of the reddish-orange emission from β-PbF₂:Eu³⁺ GCs. Simultaneously, an example of Er³⁺-doped β-PbF₂ GC was employed to demonstrate the spectral broadening effect of trivalent lanthanide ions (Ln³⁺) caused by lattice distortion and charge compensation. All these results provide insights to investigate the lattice structures of compounds and also guide researchers to design new emitting devices.