Optical limiting properties of templated Cr2O3 and WO3 nanoparticles

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The optical limiting properties of oxide ceramics nanostructures, in particular chromium (III) oxide and tungsten (VI) oxide, were investigated. The oxide ceramics were synthesized by means of a silica-based templated route leading to the synthesis of 20–30 nm particles characterized in detail by X-ray diffraction, High Resolution Transmission Electron Microscopy and N2 physisorption. Regarding the nonlinear optical characterizations when submitted to a Nd-YAG pulsed laser emitting in the nanosecond regime, the nanosized materials exhibit unique optical limiting properties compared to their micronsized counterparts. For instance a significantly higher optical power limiting was recorded for nanostructures versus micronic counterparts that could be explained by a higher surface-to-bulk atomic ratio at nanoscale. The energy thresholds for optical limiting were thus decreased by more than a factor of 8 and 4 for the Cr2O3 and WO3 nanomaterials, respectively, compared to the bulk materials. By means of transmittance measurements in an open Z-scan configuration, the nonlinear absorption coefficients for the nanosized Cr2O3 and WO3 materials were determined greater, by a factor 4 and 5, than those of the micronsized samples, respectively. Measurements in a close Z-scan setup revealed higher nonlinear refractive indices for the nanosized Cr2O3 and WO3 materials (in the order of n2 = −5 x 10−14 cm2/W versus n2 = −2 x 10−14 cm2/W for their micronsized counterparts) and additional polar scattering experiments showed that the micronsized Cr2O3 and WO3 materials display remarkably higher nonlinear scattering behavior when compared to the nanosized ones. The third order nonlinear susceptibilities χ(3) were calculated to be in the order of 10−8 esu for the nanosized materials and 10−9 esu for the micronsized ones.