Methylene Blue/PVA composite film for flexible, wide-scale UV–VIS laser cut-off filter

Abstract

Optical filter, especially the laser cut-off filter is an essential component of optoelectronics technology. In this work, we report preparation of self-standing, low cost, flexible methylene blue /poly (vinyl alcohol) composite film by simple solution casting technique for application in optical filter. Poly (vinyl alcohol) (PVA) is doped with different concentrations of the methylene blue (MB) dye (0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 5 wt%) to modify its optical properties. The structural, morphological and mechanical properties of MB/PVA composite films were investigated by x-ray diffraction, FESEM and stress-strain measurement techniques. The XRD histogram shows decrease in crystallinity in the structure of the composite films with MB doping. The optical properties of the films were studied by UV–vis spectroscopy technique which shows that transmittance of the films in the UV–vis region is decreased with increasing loading concentration of the dye in the PVA matrix. A significant decrease in the band gap of the composite is observed with MB doping. The modifications in optical properties of PVA are attributed to the interaction between the dye molecule and the PVA matrix. As prepared 3 wt% MB/PVA film having thickness ∼280 ± 20 μm can effectively block incident light of entire UV–vis region (200–695 nm) with zero transmittance(T ∼ 10−4), but remain fairly transparent in IR zone(above 705 nm), which confirms the strong potential of the composite as efficient optical filter. This work also substantiates that the 3 wt% MB/PVA composite film is able to completely block high power laser radiation (3.6 mW) of wavelength 544 nm without showing any degradation in structure with time, which makes MB/PVA a prospective candidate for high power laser cut-off filter in UV–vis region.