Cymbopogon citratus‐mediated pure aluminium oxide (Al2O3) and europium (Eu)‐doped Al2O3 with different amounts of metal ion were prepared using a green synthesis method. Synthesised nanoparticles were characterised by ultraviolet (UV)‐visible spectroscopy, photoluminescence (PL), Fourier‐transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD) and scanning electron microscopy (SEM). Synthesis of nanoparticles is confirmed by using UV‐visible spectroscopy showing maximum absorption at 411 and 345 nm for Al2O3 and Eu‐doped Al2O3, respectively. The antibacterial activity of prepared nanoparticles was evaluated against Pseudomonas aeruginosa, Streptococcus aureus, Escherichia coli and Klebsiella pneumoniae using a well‐diffusion technique. The effect of pure Al2O3 and Eu‐doped nanoparticles shows excellent results against P. aeruginosa, S. aureus, E. coli and K. pneumoniae.