Structural and optoelectrical properties of methylene blue hydrate/poly (vinyl alcohol) (C₁₆H₁₈CIN₃S·xH₂O)-PVA: A novel material for high-performance laser filters

This study reports the synthesis of low-cost and flexible methylene blue hydrate/poly (vinyl alcohol) (MBH/PVA) composite films via a simple solution casting technique for optoelectronic applications, particularly laser cut-off filters. Doping PVA with various MBH concentrations significantly enhanced its structural and optoelectrical properties. X-ray diffraction (XRD) confirmed the semi-crystalline nature of neat PVA and suggested homogeneous composite formation due to the absence of distinct MBH peaks. The average crystallite size decreased in the range of 4.38−4.06 nm upon MBH inclusion. Fourier-transform infrared (FTIR) spectroscopy revealed complex interactions between MBH and the PVA matrix. The range of bandgap change is the most crucial result. The full range is from 4.787 eV to 1.384 eV for the indirect band gap, which is a major finding. The 12.00 wt % MBH sample showed complete blocking of light across the broad spectrum of 190 nm to 820 nm (entire UV and most of the visible range). This is a very strong, quantitative performance metric for a laser cut-off filter. The extinction coefficient at the main peak (∼660–670 nm) for the 12.00 wt % MBH sample reached a value of ∼0.0048. Furthermore, the study observed variable conductivity in the polymer films dependent on MBH concentrations. These findings indicate that the prepared polymeric films exhibit decreased sensitivity to laser devices, making them promising candidates for advanced optical laser-blocking filters.