Enhanced two-photon absorption in hydrothermally synthesized La2O6Te nanorods for visible light photodetection†

Abstract

In the present study, lanthanum oxytellurate (LOT) samples with varying La : Te ratios are successfully synthesized using a simple hydrothermal method that has enormous advantages. The prepared samples crystallize in a La₂O₆Te composite phase with an orthorhombic crystal system. A nanorod-like morphology is observed for each sample, and the presence of constituent elements is verified from EDX results. Chemical compositions and their oxidation states are obtained from XPS studies. Optical studies of the materials demonstrated band gap values between 2.65 and 2.78 eV, confirming the LOT samples’ semiconducting nature. Broad photoluminescence (PL) spectra with peaks ranging between 650 and 750 nm were observed, and a red shift occurred by increasing the Te concentration in the samples. Overall, the samples exhibit good photoresponse characteristics under dark and light conditions with high I_on/I_off ratios and sensitivity values. These parameters confirm the potential of LOT materials to stand out as an alternative for susceptible and effective photodetector devices. Among the samples, LOT-2 showed 10.64 μA W⁻¹ responsivity, 5.8 × 10⁷ Jones of detectivity, and a rise and fall time of 16.25 and 23.13 s, respectively, which was the best photodetection performance compared to the other two samples. Results from the nonlinear optical (NLO) Z-scan study demonstrated the RSA behavior and valley-peak configuration with positive n₂ values corresponding to the self-focusing effect. The NLO characteristics of the materials are governed by the two-photon absorption (2PA) mechanism. Here, the LOT-2 sample displayed comparatively better results than the other two. The third-order nonlinear optical NLO susceptibility χ⁽³⁾ values suggest that LOT materials have the potential to become a new candidate for various NLO applications in the coming days.