Structural and optical properties of Cr³⁺ doped SiO₂ nanophosphor

SiO₂:x% Cr³⁺ (0 ≤ x ≤ 8) nanopowder samples were synthesized using the sol-gel method. The effect of Cr³⁺ doping concentration on the SiO₂ nanoparticles was studied for possible application in light-emitting diodes (LEDs). Structure and optical properties of undoped and Cr³⁺ doped SiO₂ nanoparticles were investigated in detail. X-ray diffraction (XRD) results confirmed the amorphous phase for undoped SiO₂ (A-SiO₂) nanopowder. However, above 0.8% Cr³⁺ there were secondary peaks due rhombohedral structure of chromium (III) oxide (R-Cr₂O₃). Ultraviolet-visible spectroscopy (UV-Vis) spectra showed a reflectance peak at around 320 nm for the undoped sample. The results showed that when the concentration of Cr³⁺ is increased there was an emergence of reflectance peaks at around 309, 419, and 553 nm which were attributed to the presence of the Cr₂O₃ lattices. The photoluminescence (PL) results revealed that with an increase in the amount of Cr³⁺, the maximum peaks in blue and near red emerge at around 2.82 and 1.89 eV, respectively. Those peaks may be due to defects within both SiO₂ and R-Cr₂O₃. The emission peaks of undoped and Cr³⁺ doped SiO₂ match well with the Uv-vis results. The international illumination colour chromaticity showed that above 0.8% Cr³⁺ the colour shifts from yellow to blue with an increase in Cr³⁺ concentration. The investigation indicated that Cr³⁺ doped SiO₂ have a potential application in blue and yellow LED chips for lighting.