Effects of Ce³⁺ concentration, beam voltage and current on the cathodoluminescence intensity of SiO₂:Pr³⁺-Ce³⁺ nanophosphor

SiO₂:Pr³⁺-Ce³⁺ phosphor powders were successfully prepared using a sol-gel process. The concentration of Pr ³⁺ was fixed at 0.2 mol% while that of Ce³⁺ was varied in the range of 0.2-2 mol%. High resolution transmission electron microscopy (HRTEM) clearly showed nanoclusters of Pr and Ce present in the amorphous SiO₂ matrix, field emission scanning electron microscopy (FE-SEM) indicated that SiO₂ clustered nanoparticles from 20 to 120 nm were obtained. Si-O-Si asymmetric stretching was measured with Fourier transform-IR (FT-IR) spectroscopy and it was also realized that this band increased with incorporation of the activator ions into the SiO₂ matrix. The broad blue emission from the Ce³⁺ ions attributed to the 5d ¹-4f¹ transition was observed from the SiO₂:0.2 mol% Pr³⁺-1 mol% Ce³⁺ phosphor. This emission was slightly enhanced compared to that of the singly doped SiO₂:1 mol%Ce³⁺ phosphor. Further investigations were conducted where the CL intensity was measured at different beam voltages and currents from 1 to 5 kV and 8.5 to 30 μA, respectively, in order to study their effects on the CL intensity of SiO₂:0.2 mol% Pr³⁺-1 mol% Ce³⁺. The electron-beam dissociated the SiO₂ and as a result an oxygen-deficient surface dead or non-luminescent layer of SiO_x, where x < 2 on the surface, was formed.