Investigations on structural, optical and second harmonic generation in solvothermally synthesized pure and Cr-doped ZnO nanoparticles

Abstract

At the forefront of the current scientific revolution of nanoscience nanocrystals (NCs), crystalline particles grown in liquid media, stand out over other classes of inorganic nanomaterials due to the high degree of control with which their crystal structure, size, shape, and surface functionalities can be engineered in the synthesis stage and to the versatility with which they can be processed and implemented into a large spectrum of devices and processes. Doped semiconductor nanostructures can yield both high luminescence efficiencies and lifetime shortening at the same time. In the present manuscript pure and Cr-doped ZnO nanoparticles were successfully synthesized from the solution phase chemistry and investigated with respect to their structural and optical properties. The resulting powder consisting of nanocrystalline particles were characterized by X-ray diffraction (XRD), UV-Visible spectroscopy, photoluminescence spectroscopy, transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray analysis (EDX) techniques. A UV emission peak was observed from the exciton transition at 380 nm in the room temperature photo luminescent (PL) spectra. The blue emission band was assigned to the Zn interstitial and vacancy level transition. Even though Cr ions are known to act as an efficient non-radiative loss centre for near band gap emission (NBE), a pronounced NBE is obtained at room temperature even for a nominal Cr concentration of 8 at. %. XRD data analysis shows that the chromium dopant atoms are incorporated into the wurtzite host lattice. The grain size decreases with increasing dopant concentration. The lattice constants extracted by the Rietveld method from XRD data vary slightly with doping concentration.