Effects of Pb2+ ions concentration on the structure and PL intensity of Pb-doped ZnAl2O4 nanocrystals synthesized using sol-gel process

Undoped and Pb2+-doped ultrafine cubic zinc aluminate (ZnAl2O4) hosts were successfully prepared at a relatively low temperature (similar to 80 A degrees C) using the sol-gel method. The concentration of Pb2+ was varied from 0 to 5 mol%. The TGA showed that the minimum annealing temperature required to obtain single phase ZnAl2O4 must be above 400 A degrees C. The XRD data revealed that all the annealed samples were single phase crystalline structures and the estimated crystallites size were in the range of 21-30 nm in diameter. The FTIR results suggest that heat-treating can destroy some of the bonds. The surface morphology of the phosphors was influenced by the Pb2+ mol%. Undoped and Pb2+-doped ZnAl2O4 nanoparticles exhibit the violet emission at slightly different positions. The slight peak shifts suggests the possibilities that the luminescence centre can either be due to the defects level in the host or Pb2+ ions. The emission peaks at 390 and 399 nm are ascribed to the typical UV transitions P-3(0,1) -> S-1(0) in Pb2+ ion. At the higher Pb2+ mol%, the luminescence quenching behaviour occurs, which suggests that doping with Pb2+ ions is accompanied by the introduction of new defect sites that enhance non-radiative recombination of the excited electrons.