LAUSR

Photoluminescence (PL) changes of ZnO nanospheres at room temperature have been measured during exposure to gases and vapors using a traditional fluorometer and a portable, ultraviolet (UV) light-emitting diode-based instrument. Thermal gravimetric analysis indicates that the nanospheres are essentially fully hydroxylated, with OH groups and H atoms attached to surface Zn and O sites, respectively. The PL spectrum has both a UV excitonic emission peak and a visible, defect-related one. Exposure to the gases and vapors studied, whether they physisorb or chemisorb, causes a decrease in the intensity of the visible emission peak relative to pure nitrogen, although to different degrees. Electron-donating molecules, such as hydrogen and methanol, cause a reversible increase in the UV emission peak intensity due to formation of an electron-rich accumulation layer around the nanoparticles. Electron-withdrawing molecules, such as oxygen and water, cause a corresponding decrease due to a depletion layer. For react...