Humidity sensing by luminescence of Eu(III)-doped mesoporous silica thin film

We report the luminescence properties of Eu(III)-doped mesoporous silica thin films (Eu-MSTFs) and their application to humidity sensing. Eu-MSTFs with ∼9 nm-sized pores ordered into a wormlike pore structure were synthesized. The Eu(III) ions inside the pores could be coordinated with 1,10-phenanthroline or 2,5-pyridine dicarboxylic acid ligand by diffusing in the ligand molecules through the pores. The ligand molecules increased the luminescence intensity of the Eu(III) ions. The luminescence intensity of the ligand-treated Eu-MSTFs varied linearly with the humidity level in the environment. The humidity sensing by this method is repeatable over many times.