Exploring the effect of boron on the grain morphology change and spectral properties of Eu3+ activated barium tantalate phosphor

Abstract

The effect of the grain morphology on the photoluminescence, charge transfer band, and decay properties was investigated by xEu³⁺, yB³⁺ (x = 10 mol%, y = 0, 5, 15, 30, 50, 70, and 100 mol%) co-doped BaTa₂O₆ ceramics fabricated by solid-state reaction. X-ray diffractions of the samples showed that the single-phase structure persisted up to 100 mol% and there was an improvement in crystallinity with increasing B³⁺ concentration. SEM micrographs of the Eu³⁺, B³⁺ co-doped grains showed that the flux effect of boron promotes grain growth and elongated grain shape. The PL emissions of the BaTa₂O₆:xEu³⁺, yB³⁺ co-doped phosphors increased up to 100 mol% B³⁺ concentration, and there was an increase in the intensities of the CTB energy ⁵D₀ → ⁷F₁ transition. The increase in PL may be attributed to the increased grain size leading to a decrease in the surface area (SA)/volume (vol) ratio with increasing B³⁺ concentration, as well as the improvement in crystallinity. However, the decrease in asymmetry ratio was related to the occupation of centrosymmetric (B) sites and the transformation from a rounded/irregular-like to an elongated/rod-like grain shape which has an increasing effect on the SA/vol ratio. The decreasing trend of the Judd–Ofelt parameters (Ω₂, and Ω₄) with the increase in boron was related to a high local symmetry of Eu³⁺ sites, and an increase in the electron density of the surrounding ligands, respectively. The increase in boron led to longer decays in the observed lifetime with bi-exponential characteristics. The CIE diagram and UV lamp photographs of the phosphors showed a color transition from red to orange associated with the increasing magnetic dipole transition. This study may provide an alternative perspective and new strategies to describe the control of grain morphology and luminescence concerning RE-doped phosphors.