Enhanced emission from Eu³⁺ in B ions doped sol-gel SiO₂ phosphors

Eu single doped and Eu, B co-doped SiO₂ xerogels and films were prepared by sol-gel process, using tetraethoxy silane, boric acid and aluminium nitrate as precursors, europium nitrate as the dopant. The influence of B ions and annealing temperature on luminescent properties of phosphors has been studied using fluorescence spectrum, X-ray diffraction and IR spectrum. The phosphors showed prominent luminescent in red. When heated up to 500°C, the emission spectrum showed six characteristic emission peaks, due to the electronic transition of⁵D₀→⁷F_J (J = 0, 1, 2, 3, 4) for Eu³⁺ respectively and the electronic transition of ⁵D₀→⁷F₁ was splited two peaks. When B ions were introduced to the Eu doped samples, the red Eu³⁺ emission was enhanced remarkably. This is because Si-O-B bonds were formed in the luminescent materials, and the symmetry of network was breached. Annealing changed the network structure and reduced the content of -OH and water, which benefits intensity of emission from Eu³⁺. The intensity of emission from Eu³⁺ quenches with increasing of annealing (up to 850°C) for probability during the annealing process, the rare earth ions may migrate and form clusters. The clustering process makes the local concentration of Eu very high and causes serious fluorescence quenching. XRD results show that the phosphor is in amorphous phase.