  The structural, optical and magnetic properties of nanostructured ZnO films
co-doped with cobalt and aluminium have been studied. The nanocrystalline
films, with cluster sizes in range 50 - 100 nm, were deposited by pulsed laser
ablation in a mixed atmosphere of oxygen and helium. The nanocrystallites have
the wurtzite structure and are highly oriented with the c-axis perpendicular to
the substrate. Both optical and electron spin resonance (ESR) spectroscopy
results show the substitutional incorporation of Co$^{2+}$ ions on the Zn site
inside the ZnO nanoclusters. The temperature dependence of the ESR spectra
follows Curie law corresponding to a paramagnetic material.
