Influence of Bi doping on the structure and photoluminescence of ZnO phosphor synthesized by the combustion method.

Bismuth doped ZnO (BZO) phosphors have been synthesized by the combustion method. The effect of Bi doping up to 4mol% on the structural, morphological, optical and photoluminescence (PL) properties have been investigated. X-ray diffraction analysis revealed that the BZO phosphors had the hexagonal wurtzite structure. The nanocrystallite size decreased from 75 to 38nm as the Bi concentration increased up to 3mol%, but then increased slightly for 4mol% Bi. The chemical states of the synthesized BZO phosphors were investigated using X-ray photoelectron spectroscopy and revealed the presence of both Bi3+ and Bi2+ charge states. The surface morphology showed spherical grains with some small particle agglomeration. The grain agglomeration and irregular shapes increased with increasing Bi concentration in the BZO phosphor. The absorption spectra were calculated from the reflection spectra using the Kubelka-Munk function and a blue shift in the absorption was obtained. The optical bandgap varied from 3.08 to 3.11eV for increasing Bi doping concentration. The PL spectra showed a blue emission at 410-500nm and a broad red peak at 650nm. These peaks are attributed to oxygen related defects in the ZnO host. The addition of Bi decreased the red emission and enhanced the blue emission.