Effects of pH on the Structural and Optical Properties of CaAl2O4: Eu2+, Dy3+ Nanoparticles

Abstract

Calcium aluminate phosphor nanomaterials co-doped with europium and dysprosium, (CaAl2O4: Eu2+, Dy3+) were prepared using a facile solution combustion technique. The structural and optical properties were investigated. The X-ray diffraction (XRD) results confirmed the presence of the monoclinic phase in all the samples. The Fourier-transform infrared analysis gave the expected chemical combustion results of the final product with few traces of Ca3Al2O6 impurities at low and very high Potential of Hydrogen (pH). The XRD patterns showed the presence of an impurity phase at low pH. This impurity phase was caused by preferential precipitation in the starting mixture due to a lack of homogeneity in the precursor mixture between the urea and metallic ions hence poor combustion. The diffraction angles of the major peaks shifted to lower 2θ for all the samples except for the sample synthesized at pH = 3.4 which shifted to higher 2θ. The crystallite sizes of the as-prepared samples were determined using the Debye-Scherrer equation. It was noted that there was variation in the crystallite sizes with a change in pH. The effect of pH was also observed in the Ultraviolet-Visible (UV-Vis) studies. It was also noted that the band gap increased with an increase in pH from 2.9 to 4.5. Scanning electron microscope (SEM) micrographs showed that all samples were agglomerated and had irregular shapes with pores and cracks. The study provides a simple route to synthesize CaAl2O4: Eu2+, Dy3+ phosphors with the optimum synthesis pH producing the most crystalline sample for application in lighting devices.