Synthesis, crystal structure, optical and adsorption properties of BaAl2O4: Eu2+, Eu2+/ L3+ (L = Dy, Er, Sm, Gd, Nd, and Pr) phosphors

In this work, the BaAl2O4: Eu2+, Eu2+/L3+ (L= Dy, Er, Sm, Gd, Nd, and Pr) phosphors were synthesized via a facile solid-state reaction method using LiCl as a flux material at 1100 °C. The structural properties, microstructure, adsorption and photoluminescence characteristics of products were evaluated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Uv–vis adsorption and photoluminescence (PL) analyses. The observation of XRD patterns showed that even 10% LiCl is not able to produce any impurity phase in BaAl2O4: Eu2+ crystal structure, although the microstructure morphology is considerably affected. The particle size of BaAl2O4: Eu2+ phosphors was about 220 nm while the use of LiCl flux resulted in a remarkable decrease of this parameter to about 120 nm. Furthermore, the PL patterns disclosed that Eu2+ ions have occupied one type of Ba2+ sites while larger quantities of lanthanides (L3+) occupied the second type of Ba2+ sites. The strongest photoluminescence emission intensity at the wavelength of 495 nm was achieved when 5 wt% LiCl was added to BaAl2O4: Eu2+. Also, the absorption analysis revealed that the addition of flux enriches the adsorption of Congo red (CR) dye on the phosphor powders. The use of 5 wt% flux material led to noticeable improvement of CR adsorption capacity from 38.53 to 48.3 mg g−1.