Micro-strain administered SHG intensity enhancement by heavy Ce doping in co-precipitated ZnO nanoparticles

Highlights: • Undoped and Ce doped ZnO nanoparticles are prepared by sol-gel co-precipitation whose sizes lie between 23 nm and 70 nm. • Band gap shows a linear decrement from 3.262 to 3.212 eV with Ce doping, due to creation of more carriers in ZnO matrix. • PL emission seen at 360 nm is due to near-band-edge transitions and the other at 380 nm due to defects level transitions. • A significant 3.5 times SHG signal intensity enhancement is observed when Ce dopant is changed from 3 to 7 at. %. • SHG signal intensity is governed by micro-strain present in samples. It rises when micro-strain falls off and vice-versa. • Flattened plant-leaves structures that are away from the symmetry, responsible for high SHG signal strength. The objective of the present study is to explore the non-linear behaviour of Ce-doped ZnO system. Undoped and Ce-doped ZnO nanoparticles of size ~23–70 nm were prepared by sol-gel co-precipitation approach. There was complete absence of Ce-containing phase until 3 at.% dopant. Band-gap decreased in a linear manner from 3.262 to 3.212 eV on doping with Ce. Emission peaks at 360 and 380 nm were observed in the PL spectra. However, at 7 at.% dopant, CeO₂ and Ce₂O₃ were observed. Interestingly, a significant increase in second harmonic generation (SHG) signal intensity of ~3.5 times was observed when the dopant concentration was increased from 3 to 7 at.% in ZnO nanoparticles. The SHG signal in doped-ZnO was governed by micro-strain such that it increased with decrease of micro-strain and vice-versa. The dependence of ZnO morphology and SHG intensity on Ce-dopant concentration in ZnO has potential for applications in bio-imaging and bio-sensing.