Effect of Eu3+ Concentration on the BaAl2O4/CaAl4O7: x% Eu3+ (0 ≤ x ≤ 5.5) Mixed-Phase Nanophosphors Synthesized Using Citrate Sol-Gel Method

Bamba Mahman,Mpho Enoch Sithole,Guang xing Liang

doi:10.1155/2021/7064183

Abstract

A series of undoped mixed-phase BaAl2O4/CaAl4O7 (hereafter called BC) and doped BC: x% Eu3+ (0 < x ≤ 5.5) nanophosphors were successfully prepared by the citrate sol-gel technique. Their structure, morphology, and optical properties were studied in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence (PL) spectroscopy. XRD and SEM showed that all the BC:x% Eu3+ samples consisted of the crystalline structure of the mixed phases of both the BaAl2O4 and CaAl4O7 materials. The structure resembles more that of the BaAl2O4 than the CaAl4O7 phase. The TEM results suggest that the crystallite sizes are in the nanometer scale with rod-like particles. PL results showed multiple emission peaks located at 436, 590, 616, 656, and 703 nm, which were assigned to the intrinsic defects within the BC matrix, 5D0 ⟶ 7F1, 5D0 ⟶ 7F2, 5D0 ⟶ 7F3, and 5D0 ⟶ 7F4 transitions of Eu3+, respectively. The decay curves evidently showed that the nanophosphors have persistent luminescence. The Commission Internationale de l’Eclairage (CIE) analysis revealed that doping has tuned the emission colour from blue to orange-red. The results indicate that the Eu3+-doped samples can potentially be used in the orange/red-emitting phosphors.

Highlights

IntroductionFluorescence phosphors such as calcium aluminates (CaAl2O4 and CaAl4O7), which are good examples of the materials exhibiting a long lasting afterglow, have found application in light-emitting devices such as plasma display panels, medical lamps, and fluorescent lamps [8]
Yerpude et al [22] have prepared a BaCa2Al8O15 : Eu2+, Dy3+ phosphor using the combustion method. ey observed a broadband excitation spectrum, which peaks at 334 nm when monitoring the emission at 435 nm and that was assigned to the 4f55 d1 ⟶ 4f7 transition of Eu2+. ey observed blue long-lasting phosphorescence (BLLP) for several minutes in the dark when the light source was removed. e BLLP was attributed to the presence of Dy3+ ions which act as hole traps. ere was no emission from Eu3+ suggesting that all the Eu3+ ions in the crystal matrix had been completely reduced to Eu2+ [15, 23]
The solutions were heated at temperatures ∼80°C for 3 h under constant stirring using a magnetic stirrer to obtain gels. e gels were dried at room temperature for 12 h to allow enough gelling. e gels were calcined in a furnace at 1000°C for 3.5 h. is is because CaAl4O7 crystallizes directly at 883°C [27]. e product from the furnace was crushed in an agate mortar with a pestle for powder synthesis. e ground and pulverized powders were taken for characterization using different analysis techniques

Summary

Introduction

Fluorescence phosphors such as calcium aluminates (CaAl2O4 and CaAl4O7), which are good examples of the materials exhibiting a long lasting afterglow, have found application in light-emitting devices such as plasma display panels, medical lamps, and fluorescent lamps [8] To this end, the europium ions can be introduced into the CaAl2O4, CaAl4O7, or BaAl2O4 lattice in its trivalent (Eu3+) or divalent (Eu2+) state or both of them at the same time [9]. Ere was no emission from Eu3+ suggesting that all the Eu3+ ions in the crystal matrix had been completely reduced to Eu2+ [15, 23] It is clear from the above studies that mixed phases in phosphors have more exceptional luminescence and fluorescence performance than singlephase phosphors.

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