Structural characteristics and effective two photon absorption induced optical limiting behavior of Co2+ doped monoclinic LaPO4 nanostructures

Abstract

The Nonlinear optical limiting properties of pure and Co2+ doped monoclinic LaPO4 nanostructures synthesized by co-precipitation technique is reported. The Structural confirmation of Co2+ doped LaPO4 nanostructures is studied by X-ray diffraction (XRD) and Raman spectra. The replacement of larger La3+ ion by smaller Co2+ ion is confirmed by the shift of XRD and Raman scattering lines. X ray photoelectron spectroscopy (XPS) survey spectrum of 0.3 % Co2+ doped sample confirms the presence of lanthanum (La). Phosphor (P), oxygen (O) and Cobalt (Co) elements. Transmission electron microscopy (TEM) image portrays the formation of nearly mono-dispersed spherical particle with diameter of 48 nm. The absorption spectra reveals a blue shift in absorption edge with additional peak at 580 nm upon Co2+ doping. Photoluminescence emission spectra shows blue green emission with major peak at 440 nm. Open aperture (OA) Z-scan technique excited at 532 nm with a nanopulsed Nd: YAG laser revealed pure and Co2+ doped LaPO4 exhibits reverse saturable absorption ascribed due to two photon absorption (2PA). Intensity dependent OA measurements shows that the nonlinear absorption coefficient remains constant with varying input on-axis intensity, ensuring genuine 2PA for pure sample. While for Co doped sample, the nonlinear absorption coefficient varies with input on-axis intensity, assuring the occurrence of sequential 2PA. Co doped samples exhibit enhanced nonlinear absorption due to synergistic influence of Co2+ in LaPO4 crystal structure. Optical limiting action induced by 2PA in LaPO4 with lower onset limiting ensures the potentiality of the chosen material for photonic applications.