Origin of intense blue-green emission in SrTiO3 thin films with implanted nitrogen ions: An investigation by synchrotron-based experimental techniques

Abstract

The present study utilizes synchrotron-based x-ray diffraction (XRD), photoluminescence (PL), and x-ray absorption near edge structure (XANES) spectroscopic techniques to comprehend the evolution of optical intense blue-green emission in 100 keV nitrogen (N) ion implanted $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ (STO) thin films deposited by RF magnetron sputtering technique. The XRD pattern shows a shift in reflections at lower N ion fluences and the amorphization of the films at higher fluences. A disordered phase induced by implantation in the STO films leads to an intense blue-green emission due to oxygen (O) vacancies and N ($2p$) bound states. A schematic diagram of energy levels has been proposed to explain the origin of PL emission. The XANES spectra at Ti $K$ edge reflect a change in the valency of Ti ions and the local atomic structure of ordered and disordered phases of STO with an increase in N ion fluence. The splitting of peak assigned to ${e}_{g}$ orbitals, and discrepancy in ratio ${d}_{{z}^{2}}/{d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ observed in the Ti $L$- and O $K$-edge spectra, confirm a distortion in $\mathrm{Ti}{\mathrm{O}}_{6}$ octahedral structure and modifications in O $2p$-Ti $3d$ hybridization states. The synchrotron-based techniques reveal that N ion implanted STO can be a good photoluminescent material exhibiting a variety of emissions through bound states of O vacancies and implanted N ions.