Hierarchical 2D Mn-Co-Te nanocomposites for visible light photodetector and nonlinear applications: insights from experiment and DFT.

MnTe and CoTe have attracted significant attention in the field of optoelectronics due to their promising electronic and optical properties. In the present work, ternary Mn-Co-Te nanocomposites with varying Mn and Co concentrations were successfully synthesized via a hydrothermal approach to investigate the compositional influence on their structural, optical, photoresponsive, and nonlinear optical properties. From X-ray diffraction (XRD) analysis, the crystallite size was found to decrease from 30.244 to 17.370 nm with decreasing Mn concentration, while Raman spectroscopy revealed the characteristic vibrational mode associated with Te-Te bonding. Field emission scanning electron microscopy (FESEM) demonstrated the formation of hierarchical nanosheet-like structures embedded with nanoparticles, whereas X-ray photoelectron spectroscopy (XPS) studies confirmed the surface chemical states and elemental composition of the synthesized composites. Optical investigations revealed a gradual increase in the direct bandgap energy from 2.74 to 3.34 eV with increasing Co concentration. Photoresponse measurements showed significant photocurrent enhancement under illumination, with the Mn-rich sample (MCT-1) exhibiting the highest photocurrent value of 104.06 mA. Furthermore, nonlinear optical studies carried out using the Z-scan technique demonstrated prominent reverse saturable absorption (RSA) behavior along with positive nonlinear refractive index values. The calculated third-order nonlinear susceptibility was found to be of the order of 10-10 esu, confirming strong nonlinear optical activity. These results suggest that Mn-Co-Te nanocomposites are promising materials for optoelectronic and nonlinear photonic applications.