Most of the existing photovoltaic (PV) solar cells are already optimized in terms of their absorption and conversion efficiency, however any strategy that can help to raise their efficiency is welcome, especially if it is cheap and does not require any modification of the solar cell fabrication technology. One possibility to increase solar cell's efficiency is the use of a material that could convert the high energy photons from the sun spectrum, namely UV and blue light, which are otherwise inefficiently absorbed by the amorphous Si, CdTe, CIGS and organic PV cells, and re-emit them as lower energy photons, for which the conversion efficiency of these cells is optimal. This so-called “down-shifting”. We study down-shifting materials based on ZnO nanoparticles. It naturally absorbs the blue and UV light thanks to a wide band gap of about 3.37 eV and it can also emit visible light, from yellow to red, depending on the nature of the crystalline and surface defects involved in the emission process. We present a quick and convenient chemical solution approach to get unique mesospheric self-assembly hybrid ZnO system with intense photoluminescent quantum yield of 40-75 % and stable visible emissions. Furthermore, the possibility of application of other ZnO nanostructures, namely zinc oxide nanowires, in gas sensors, is presented. Their excitonic and visible emission is studied in the presence of gas vapors and the results demonstrate the change of the visible photoluminescence of ZnO nanowire array and that the material is able to adsorb gases.