Structural and optical properties of Cr3+ doped SiO2 nanophosphor

SiO 2 :x% Cr 3+ (0 ≤ x ≤ 8) nanopowder samples were synthesized using the sol-gel method. The effect of Cr 3+ doping concentration on the SiO 2 nanoparticles was studied for possible application in light-emitting diodes (LEDs). Structure and optical properties of undoped and Cr 3+ doped SiO 2 nanoparticles were investigated in detail. X-ray diffraction (XRD) results confirmed the amorphous phase for undoped SiO 2 (A-SiO 2 ) nanopowder. However, above 0.8% Cr 3+ there were secondary peaks due rhombohedral structure of chromium (III) oxide (R-Cr 2 O 3 ). 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 Cr 3+ is increased there was an emergence of reflectance peaks at around 309, 419, and 553 nm which were attributed to the presence of the Cr 2 O 3 lattices. The photoluminescence (PL) results revealed that with an increase in the amount of Cr 3+ , 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 SiO 2 and R-Cr 2 O 3 . The emission peaks of undoped and Cr 3+ doped SiO 2 match well with the Uv-vis results. The international illumination colour chromaticity showed that above 0.8% Cr 3+ the colour shifts from yellow to blue with an increase in Cr 3+ concentration. The investigation indicated that Cr 3+ doped SiO 2 have a potential application in blue and yellow LED chips for lighting.