Synthesis and characterization of a Eu3+ -activated Ba2-x V2 O7 :xEu3+ phosphor using a hydrothermal method: a potential material for near-UV-WLED applications

Abstract

Eu³⁺ -activated Ba₂ V₂ O₇ (Ba_2-x V₂ O₇ :xEu³⁺ ) phosphor materials were synthesized using a hydrothermal method and different concentrations of europium (x = 0.01, 0.02, 0.03, 0.04, and 0.05%). Phase purity, structural, morphological, optical, and luminescence characteristics of the as-synthesized phosphors were studied using powder X-ray diffraction (XRD), high resolution scanning electron microscopy, UV-visible spectroscopy, and fluorescence spectrometry. The recorded XRD patterns of the as-synthesized phosphors were indexed and predicted to be a triclinic structure. A cube-like morphology was obtained for the as-prepared samples. Broad absorption in the UV region from 200 nm to 380 nm was observed and the good transparency in the visible region at 400-800 nm originated from the [VO₄ ]^3- group charge transfer (CT) transition. The broad emission peak centred at 499 nm was due to the CT band of the [VO₄ ]^3- group. Also, a sharp peak observed at 613 nm was due to the electric dipole transition of ⁵ D₀ →⁷ F₂ of Eu³⁺ ions that occupied the lattice sites without inversion symmetry for all concentrations. The colour qualities of the as-prepared samples were calculated using Commission International de l'Eclairage coordinates. The colour-rending index (CRI) value was 86 for the Ba_1.97 V₂ O₇ :0.03Eu³⁺ phosphor. Furthermore, a WLED with a high CRI value of 95 was achieved by coupling the 3 W 356 nm near-UV light-emitting diode (LED) chip with the Ba_2-x V₂ O₇ :xEu³⁺ phosphor. These results suggested that the as-prepared phosphor materials are potential candidates for fabrication of near-UV chip excited WLEDs.

Keywords: Eu3+ ions; colour-rending index; electric dipole transition; hydrothermal method; luminescence.