Microwave-Assisted Synthesis of BaTe2O5 Nanosheets for Visible-Light Photodetection and NLO Applications

Barium tellurium oxide (BaTe2O5) nanosheets are promising multifunctional materials for optoelectronic and nonlinear photonic applications. However, their nanoscale synthesis and structure–property relationships as a function of microwave power have not been sufficiently explored. The BTO nanosheets were synthesized using a quick microwave-assisted method at 360, 540, and 720 W for a constant irradiation time. Their structural, morphological, optical, photodetection, and nonlinear optical features were thoroughly investigated. The analyses of XRD, Raman, XPS, FESEM, TEM, and EDX confirm the formation of crystalline BTO with an interconnected nanosheet morphology, while increasing microwave power promotes crystallization and morphological evolution toward thinner, more interconnected nanosheets. The optical bandgap is tunable in the range of 1.71 to 2.28 eV, with a reduction in defect-mediated radiative recombination at higher microwave power. Notably, BTO-720 shows the best photodetection performance with a responsivity of 3.405 AW–1 and detectivity of 2.4 × 1010 Jones, along with stable ON/OFF photoresponse characteristics. The Z-scan measurements also indicate third-order nonlinear optical behavior, with saturable absorption and positive nonlinear refraction, with BTO-720 exhibiting the strongest nonlinear response. More consistent explanations for the nonlinear absorption involve saturable and defect-assisted carrier processes rather than two-photon absorption. The results indicate that microwave power is a useful parameter for tuning the structure and function of BTO nanosheets and that they possess potential for visible-light photodetection and nonlinear photonics.