Optical characterization of in-situ generated Cu2O excitons in solution derived nano-zirconia film matrix

Abstract

Abstract Cu2O excitons were generated in-situ in a nano-zirconia film matrix on silica glass substrate from the precursor solution containing Cu(II) nitrate trihydrate and zirconium oxychloride octahydrate. The films were annealed in the temperature range 200–1200 °C and characterized by transmission electron microscopy (TEM), UV-VIS-NIR and fluorescence spectroscopy. In the UV-VIS spectra of the films most of the UV and visible bands shifted towards longer wavelengths with increasing annealing temperature and the corresponding Cu2O microcrystallite size was evaluated from the shifting of the UV bands (271–371 nm). Wannier hydrogen-like excitonic transitions, e.g., blue, green, yellow series of Cu2O excitons were observed in the visible region. Excitation dependent fluorescence bands were observed in the visible region and the 400 nm excitation depicted two distinct fluorescence bands in the green (~ 525 nm) and red (~ 630 nm) regions. The intensity ratios of green and red fluorescences and vice versa were found to be dependent on the microcrystallite size. Tentative band assignments have been proposed from the excitonic absorption and fluorescence bands.