In recent years, metal oxide semiconductor nanoparticles have gained attention for their unique optical properties due to quantum confinement effect. The nonlinear optical (NLO) properties of semiconductor nanoparticles have attracted much attention for optoelectronic applications, because of their large optical nonlinearity and short response time 1, 2.
Amongst many metal oxides, ZnO nanostructures is one of the most promising low cost wide band gap semiconducting material, has attracted the attention owing to its excellent optical and electrical properties which makes them suitable for various applications such as solar cells, nano-optoelectronic devices, varistors, transparent high power electronics, electroluminescent devices and nonlinear optical devices 3-5. The large exciton binding energy (60 meV) and wide direct band gap (3.37 eV) of ZnO at room temperature is well known 6. A number of reports have been reported on the linear optical properties of nanocomposites consisting of ZnO and other materials. Materials with high nonlinear optical properties are essential for fabrication of device for optical switching and optical limiting applications. Second- and third-order nonlinear optical properties of ZnO were studied for applications in nonlinear optical limiting and fast optical switching 7. Modification of ZnO with suitable dopant can generate new and interesting NLO properties suitable for optoelectronic applications. Doping of appropriate metal ions with metal oxide creates Quasi –stable energy states which increase the electrons trapping due to higher surface sites and variation in band gap energy (Eg).
Doping of alkaline earth metal ions is the best choice than transition metals because the presence of localized d-levels in transition earth metals doping can reduce the photo threshold energy efficiency of semiconductors8. Strontium is one of the important alkaline-earth metals widely used for many applications including the electronics, metallurgy, chemical industry, military industry and optics; it is also believed to be a good potential candidate material when doped with ZnO nanostructures 9. However, a detailed study of effects of strontium doping on ZnO characteristics is rarely reported so far. Recently the band-gap tuning and enhanced white light emission in ZnO:Sr nanorods have reported by few researchers 10. Although some studies of ZnO have been reported in the field of nonlinear optics, only a few reports are available for the study of thermally induced (CW laser) third order nonlinearity of ZnO nanostructures. To the best of our knowledge, third-order nonlinear optical properties of Sr doped ZnO on the progression of nonlinear optical properties has not been reported thus far. Hence, the goal of the present research work is to investigate the influence of Sr on the nonlinear optical properties as well as optical limiting under the diode-pumped Nd: YAG laser illumination.