Formaldehyde gas sensor based on silver-and-yttrium-co doped-lithium iron phosphate thin film optical waveguide

Several formaldehyde gas sensors were fabricated using silver-and-yttrium-co doped-lithium iron phosphate (LiFe1−0.01xY0.005xAg0.005xPO4)-thin-film-based optical waveguides (OWGs). LiFe1−0.01xY0.005xAg0.005xPO4 powders with different concentrations of the dopants Ag and Y were prepared in high purity via a one-step hydrothermal method, and characterized using their X-ray diffraction patterns and energy dispersion spectra. The obtained powders were subsequently utilized in a spin-coating procedure for the fabrication of LiFe1−0.01xY0.005xAg0.005xPO4 thin films. tained thin films were characterized by refractive index, thickness, attenuation, and sensing properties to formaldehyde at room temperature. The response of LiFe1−0.01xY0.005xAg0.005xPO4-thin-film/tin-diffused-glass-based optical waveguide sensors to formaldehyde was higher than their responses to other VOCs. For a set of formaldehyde concentrations ranging from 1 ppb to 1000 ppm, the sensitivity of the sensors increased with a decrease in the dopant concentrations. Moreover, the ability to be used repeatability as well as the selectivity of the sensors was tested using lower gas concentrations; at the lower concentrations (below 250 ppm), the sensor only responsive to formaldehyde gas.