Optical Waveguide BTX Gas Sensor Based on Yttrium-Doped Lithium Iron Phosphate Thin Film

Yttrium-doped LiFePO4 powder was synthesized using the hydrothermal method in one step and was used as a sensing material. An optical waveguide (OWG) sensor based on Yttrium-doped LiFePO4 has been developed by spin coating a thin film of LiFe0.99Y0.01PO4 onto a single-mode Tin-diffused glass optical waveguide. Light was coupled into and out of glass OWG employed by a pair of prisms. The guided wave transmits in waveguide layer and passes through the film as an evanescent wave. The sensing film is stable in air, but when exposed to target gas at room temperature, its optical properties such as transmittance (T) and refractive index (nf) were changed; thus, the transmitted light intensity was changed. The LiFe0.99Y0.01PO4 thin film OWG exhibits reversible response to xylene gas in the range of 0.1–1000 ppm. When the concentration of BTX gases was lower than 1ppm, other substances caused a little interference with the detection of xylene vapor. Compared to pure LiFePO4 thin film OWG, this sensor exhibited higher sensitivity to BTXs.