Influence of Annealing Temperature and Gd and Eu Concentrations on Structure and Luminescence Properties of (Y,Gd)BO₃:Eu³⁺ Phosphors Prepared by Sol–Gel Method

Abstract

Red-emitting Eu³⁺-doped (Y,Gd)BO₃ phosphors have been synthesized by a sol–gel process using metal oxides and boric acid as starting materials and citric acid as chelating agent. The main factors affecting the structure and luminescence properties of the product, such as sintering temperature, chemical composition, and Eu³⁺ doping concentration, were investigated. X-ray diffraction (XRD) analysis indicated that the phosphors begin to crystallize at sintering temperature of 700°C and become phase pure at 900°C. The average size of the phosphor particles after sintering at 1000°C was determined to be about 30 nm to 50 nm. The (Y,Gd)BO₃:Eu³⁺ phosphors were found to exhibit strong red emission at 611 nm and 625 nm corresponding to the ⁵D₀–⁷F₂ transitions of Eu³⁺ in the host lattice. The photoluminescence intensity was enhanced by posttreatment at 900°C and remained unchanged at 1000°C. It was also found that the optimal concentration of Gd³⁺ ions for Eu³⁺ emission was 35%, and no concentration quenching of the photoluminescence was observed even at Eu³⁺ doping concentration up to 30%.