Effect of humidity on photoluminescence from Ru(bpy)32+ incorporated into a polysaccharide solid film and its application to optical humidity sensor

The effects of humidity on photoluminescence from Ru(bpy)32+ dispersed in polysaccharide solid films have been investigated. In a κ-carrageenan solid film, peaks of relative emission intensity (IR) and lifetime (τ) appeared around 20% (under Ar) and 30% (under air) relative humidity (RH). In a chitosan solid film, only small changes were observed in IR and τ of the photoluminescence up to 20% RH. However, over 20% RH, the IR and τ decreased with the increase in RH These results were interpreted by mobility of Ru(bpy)32+ as well as electrostatic and hydrophobic interactions between polysaccharide and Ru(bpy)32+. Larger effect of humidity was observed under air than under Ar depending on the polysaccharide used, which was explained by the quenching reaction by the O2 dissolved in water phase in the polysaccharide domain.