Sol–gel prepared Cu₂O microspheres: linear and nonlinear optical properties

We report the simple sol–gel based synthesis of size-tunable monodispersed crystalline Cu₂O microspheres (CMS) and the measurement of their linear and nonlinear optical properties. Optical absorption spectra show a broad plasmonic absorption band extending from 350 to 1100 nm in general agreement with calculations based on Mie theory, despite the relatively large micron size of the particles. Z-scan measurements (532 nm, 5 ns pulses) reveal that Cu₂O microspheres are efficient optical limiters, comparable in strength to nanocarbons and metal/semiconductor nanoparticles. The effective two-photon absorption coefficients are numerically calculated from measured data. These can be tuned systematically by varying the particle size.