Excited state absorption assisted optical limiting action of Fe decorated γ-BBO nanorods

Abstract

Excited state absorption (ESA) assisted optical limiting behavior of hydrothermally prepared Fe decorated γ-Barium Borate (BBO) with three different concentrations (0.01, 0.03 and 0.05 M) are investigated by Z-scan using nanopulsed Nd:YAG laser (532 nm, 9 ns, 100 μJ). XRD confirms the formation of γ-BBO (JCPDS No. 01-071-2501) and incorporation of dopants (small shift in peak position at 2θ = 26.09° and 29.74°) without altering the phase composition. Morphology reveals the deposition of Fe nanoparticles upon the flat facet nanorods and increasing Fe dopant level reduces the diameter of γ-BBO nanorods. In Fe3+ decorated γ-BBO nanorods, the absorption peak at 200–240 nm were due to П→П* transition of BBO and new broad peak at 290–420 nm correspond to the incorporation of Fe ion. At higher dopant concentration (0.05 M), red shift in band from 302 nm to 416 nm ascertained the change in transition from 6A1g (S) → 4T2g (D) to 6A1g (S) → 4T2g (G). Also, shift in near band edge emission (NBE) towards higher wavelength in PL spectra confirms the alteration in band structure of γ-BBO due to incorporation of Fe3+ ions into the host-lattice. The open aperture Z-scan curve shows the presence of reverse saturable absorption and the measured data fits well to the model for effective two photon absorption originating from sequential 2 PA (1 PA + ESA) process. Concentration of dopants and morphology of γ-BBO nanorods alters the band structure which induces an enhanced nonlinearity along with a variation in NLO coefficients. 0.05 M Fe decorated γ-BBO nanorods possess maximum 2PA coefficient (1.77 × 10−10 m/W) and lowest onset optical limiting threshold (0.98 × 1012 W/m2) due to the higher loading of Fe3+ ions and size-reduced γ-BBO nanorods. Therefore Fe decorated γ-BBO nanorods are superior than pristine γ-BBO nanorods and can be used as a potential ESA assisted optical limiting material under nanosecond excitation at 532 nm.