Phase segregation induced third order nonlinear saturable absorption behavior in Erbium doped ZnO nanoparticles synthesized by facile hydrothermal method

Abstract

Abstract Here in this work, we present the dominance of rare earth dopant (Er) in association with the surfactant (Oleylamine) on the structural, surface morphology, optical, and nonlinear optical properties of hydrothermally grown ZnO nanoparticles. The polycrystalline nature of the prepared nanostructures is confirmed by the XRD diffractograms. The formation of erbium related compound (erbium oxide) in the highest Er doped ZnO nanoparticles is visible from the XRD diffractogram. The incorporation of Er at different doping concentrations (1 at. wt.%, 3 at. wt.%, and 5 at. wt.%) brings noticeable morphological changes in the FESEM images. The Raman spectra reveal the retention of wurtzite structure in undoped and Er doped nanoparticles. The disappearance of A1 (TO) mode in ZnEr3 and ZnEr5 nanoparticles shows the deteriorated polar lattice bond strength. The phase segregation observed from XRD spectrum of ZnEr5 nanoparticles is further confirmed by the detection of local vibrational mode (LVM). A severe decrement in the bandgap of the Er doped nanoparticles is noticed from UV–Vis spectroscopy. A continuous fall in the intensity in the NBE emission with increasing Er doping concentration is attributed to the formation of surface defects below the conduction band edge. The nonlinear optical parameters of the nanoparticles are quantified with the assistance of open aperture and closed aperture Z-scan curves. A remarkable switching from reverse saturable absorption (RSA) to saturable absorption (SA) and self-defocusing to self-focusing mechanisms in ZnEr5 shed light on the impact of phase segregation on the nonlinear response of the Er doped nanoparticles. The quantified values of nonlinear parameters look promising in the fabrication of photonic devices.