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†
Abstract
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 (Fi−) (Eu3+ + Fi− = 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 D4d 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 Oh to D4d, C4v, C3v, C2v, 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.