Visible luminescence from highly textured Tb3+ doped RF sputtered zinc oxide films

Abstract Highly transparent, luminescent, c-axis oriented Tb 3+ doped ZnO films are prepared by RF magnetron sputtering technique. The structural, morphological, optical and luminescence properties of these films are investigated as a function of Tb 3+ doping concentration by X-ray diffraction (XRD), micro-Raman spectroscopy, atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), spectroscopic ellipsometry, UV-Visible spectroscopy and photoluminescence spectroscopy. The as-deposited films are found to be highly crystalline with wurtzite hexagonal phase of ZnO. The characteristic features of hexagonal wurtzite structure of ZnO, particularly the appearance of non-polar E 2 modes are easily identified from the Raman spectra of the films. The surface morphology of the films revealed by FESEM and AFM images present a dense distribution of grains. The elemental analysis carried out using energy dispersive X-ray (EDX) spectra confirms the incorporation of Tb 3+ ions in the ZnO lattice. The films are highly transparent in the visible region. Using ellipsometric analysis, the variation of refractive index, dielectric constant and thickness of the films are studied as a function of Tb 3+ doping concentration. The photoluminescence spectra of the Tb 3+ doped ZnO films recorded using an excitation radiation of wavelength 325 nm from a He-Cd laser exhibit visible luminescence ~430, 490, 516 and 542 nm. The origin of visible emissions ~490 and 542 nm in the doped films can be attributed to 5D 4 →7F 6 and 5D 4 →7F 5 transition of Tb 3+ ion respectively. The intensity of the emission at 542 nm is found to be decreasing at higher doping concentration due to concentration quenching effect. The blue emission in the films can be attributed to the electron transition from shallow donor level formed by interstitial Zn atoms to the top of the valence band. The origin of the visible emission ~516 nm is attributed to antisite oxygen defects in ZnO.