Structural, optical and photoluminescence properties of Eu doped ZnO thin films prepared by spin coating

Eu³⁺ doped ZnO thin films were successfully prepared using the spin coating technique. X-ray diffraction confirmed that the undoped films had high crystallinity and preferred orientation along the c-axis, although the crystallinity and the preferred orientation deteriorated with increasing Eu³⁺ doping concentration. The average particle sizes estimated from atomic force microscopy and the optical band gap of ZnO were found to decrease with increasing Eu³⁺ concentration. The films were excited at 325 nm using a He-Cd laser and at 464 nm using a Xenon lamp. Upon excitation at 325 nm, the films exhibited band to band emission at ∼378 nm and a broad deep level emission due to defects with a small peak associated with characteristic Eu³⁺ emission at 614 nm that protruded from the deep level emission. Upon excitation at 464 nm the characteristic Eu³⁺ emission features were observed and their intensity increased with increasing Eu³⁺ content, reaching a maximum intensity at 0.6 mol% of Eu³⁺, and then decreased with a further increase in the Eu³⁺ concentration. The critical distance associated with quenching was calculated as 1.6 nm, indicating that the multipole-multipole interaction was responsible, although defects created due to the differences in ionic radii and charge states of Eu³⁺ and Zn²⁺ would also have contributed to luminescence quenching. Judd-Ofelt intensity parameters (Ω₂)and asymmetry ratio analysis revealed the proportional dependency of the Eu³⁺ emission intensity to the local environment around the Eu³⁺ ions in the host, where the higher intensity observed at the higher Ω₂ and asymmetry ratio values for the sample with 0.6 mol % of Eu³⁺. Eu³⁺ ions were successfully incorporated into the ZnO matrix and their effects on the ZnO thin film structure, optical and photoluminescence properties were investigated.