Time-dependent laser irradiation-induced kinetics of changes in linear-nonlinear optical properties of Bi15In20Se65 thin films for IR applications

The current research depicts the laser irradiation-induced effect on the optoelectrical and structural properties of thermally evaporated Bi15In20Se65 thin films with different exposure durations (0, 10, 20, 30, 60, and 90 min). The illumination effect under different lasing times leads to the retention of amorphous nature, indicating the short-range ordering inside the matrix. An improvement in the homogeneous and smooth texture of the film surface even after irradiation has been observed. However, significant optical changes have been noticed with different exposure durations. Transparency decreased with the exposure time, whereas an increment in the absorption coefficient with red shifting in the absorption edge was observed. Broad transparency and less absorption over the infrared region make these films promising for infrared optics such as temperature detection, energy management, monitoring, night vision, etc. Laser illumination allowed bond rearrangements that led to an increase in defect states over the forbidden gap regime and reduced the bandgap from 1.02 to 0.94 eV, confirming the photodarkening nature. This consequently enhanced the Urbach energy and electron-phonon interactions. Both extinction coefficient and refractive index enhanced with lasing duration, indicating an increment in the scattering centers with the lasing duration. The increase in the lasing time results in the increase of interband transitions, which might be due to the increase of carrier concentrations in the system. The non-linear susceptibility (chi((3))) and refractive indices showed enhancement with exposure duration. The observed non-linear refractive index (SI) is 20-30 times greater than silica. This reduction of E-g and enhancement in non-linearity improves the occurrence of two-photon absorption, signifying the potentiality for photonic devices. The hydrophilic nature of laser-irradiated films makes them suitable for applications such as self-cleaning, antifouling, and antifogging as coating materials.